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UBC Theses and Dissertations

A survey of the galactic plane for variable radio emission Taylor, A. R. 1982

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A SURVEY OF THE GALACTIC PLANE FOR VARIABLE RADIO EMISSION by ANDREW RUSSELL TAYLOR B . S c , U n i v e r s i t y of Western O n t a r i o , 1976 M.Sc, U n i v e r s i t y of B r i t i s h Columbia, 1978 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES ( Department of P h y s i c s ) We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA J u l y 1982 © Andrew R u s s e l l T a y l o r , 1982 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date ADDENDUM The catalogue of sources included i n t h i s thesis represents analysis of only the f i r s t 40% of observations of the survey area. As such, i t i s preliminary i n nature. Further analysis, based on a d d i t i o n a l information from completed observations of the entire survey, has led to the d e l e t i o n o a f r a c t i o n of the f a i n t , non-variable sources l i s t e d . While not a f f e c t i n g the conclusions of the thesis, the catalogue presented here should be used with caution and not referred to i n the l i t e r a t u r e . The f i n a l source catalogue i s published i n the Astronomical Journal, v o l . 88, (1983) p. 1784 i i ABSTRACT Observations have been c a r r i e d out to survey the northern g a l a c t i c plane f o r sources of h i g h l y v a r i a b l e r a d i o emission at 5 GHz. To over—come the b i a s e s of pre v i o u s searches f o r v a r i a b i l i t y , the survey i s conducted by making repeated and systematic o b s e r v a t i o n s of the survey r e g i o n , c o n s i s t i n g of the area w i t h i n about ±2° of the g a l a c t i c plane i n the l o n g i t u d e i n t e r v a l of 40° to 220°. T h i s t h e s i s presents the a n a l y s i s and r e s u l t s of the f i r s t t h ree years of o b s e r v a t i o n s , comprising 40% of the t o t a l survey. The o b s e r v a t i o n s were c a r r i e d out f o r a t o t a l of 3 months, i n August of 1977, 1978 and 1979, and cover an area of over 200 square degrees, with a r e s o l u t i o n of 3'. Within t h i s a rea, a t o t a l of 806 compact r a d i o sources have been d e t e c t e d . The catalogue i n c l u d e s sources with f l u x d e n s i t y as low as 15 mJy, and i s complete down to 70 mJy. Of these sources, 758 have been examined f o r v a r i a t i o n on a time s c a l e of a few days ( s h o r t — t e r m ) , and 434 f o r v a r i a t i o n s on time s c a l e s of one or two years (long—term). Twenty—three new v a r i a b l e r a d i o sources have been d i s c o v e r e d ; 12 short—term and 11 long—term. An a d d i t i o n a l 18 sources are p o s s i b l y v a r i a b l e . The amplitudes of the long—term v a r i a t i o n s are s i m i l a r to those of known e x t r a g a l a c t i c v a r i a b l e s . A number of short—term v a r i a b l e s e x h i b i t much l a r g e r v a r i a t i o n s . The l o n g i t u d e d i s t r i b u t i o n suggest that the m a j o r i t y of short—term v a r i a b l e s are g a l a c t i c , with l u m i n o s i t i e s i n the range 1 O 3 0 — 1 0 3 5 e r g s — s " 1 . T h i s l u m i n o s i t y range i s s i m i l a r to that of the strong X—ray b i n a r i e s sources, such as Cyg X-3, SS 433 and Sco X-1. To date, extensive follow—up o b s e r v a t i o n s have been c a r r i e d out f o r only one of the v a r i a b l e sources d i s c o v e r e d . T h i s source (GT0236+610) i s p e r i o d i c , undergoing a r a d i o o utburst every 26.52 days. The source i s p o s i t i o n a l l y c o - i n c i d e n t with the BO s t a r LS 1+61°303 and t h i s i d e n t i f i c a t i o n has been confirmed by Gregory et a l . (1979). GT0236+610 i s an X-ray source (Share et a l . 1978, Bignami et a l . 1980) and, i n a d d i t i o n , i s the most probable c o u n t e r p a r t of the COS B r- r a y source CG135+01 (Gregory and T a y l o r 1978, P o l l o c k et a l . 1981 ) . Another h i g h l y v a r i a b l e source (GT2116+493) i s a l s o found to be c o — i n c i d e n t with a s t e l l a r o b j e c t . T h i s source i s probably an RS CVn type binary at a d i s t a n c e of about 300 pc. Comparison of source counts from the catalogue of compact sources, to e x t r a g a l a c t i c r e s u l t s , show that >200 of the compact sources, with f l u x d e n s i t y l e s s than 60 mJy, are g a l a c t i c . The non—variable g a l a c t i c sources are l i k e l y to be small HII regions w i t h i n 6 kpc of the sun. iv CONTENTS Page Abstract . i i L i s t of Tables v i i L i s t of Figures v i i i I INTRODUCTION 1 1. Variable Radio Sources 2 1.1 Extragalactic 2 1 .2 Galactic 6 2. Observational Short-comings 11 II THE SURVEY 16 1. Instrumentation 16 2. Observations 21 2. 1 Method 21 2.2 Coverage 29 III CALIBRATIONS 34 1 . Introduction 34 2. Instrumental P r o f i l e s 39 3. Gain and Pointing 54 3.1 1979 55 3.2 1978 60 3.3 1977 63 4. Uncertainties 66 IV SEARCH FOR COMPACT SOURCES 73 1. Introduction 73 2. Editing 74 3. The Search 76 3.1 Method 76 3.2 Spurious and Extended Sources 82 3.3 Estimation of Source Strength and Position .... 90 4. Monte Carlo Simulations 93 V MEASUREMENT OF VARIABILITY 107 1. Short-Term Variations 107 1 . 1 Method 107 1.2 Instrumental Variations 111 1.3 Monte Carlo Simulations 115 2. Long—Term Variations 121 2.1 Method 121 2 . 2 Limitations 1 28 VI THE CATALOGUE OF COMPACT RADIO SOURCES 130 1. Introduction 130 2. The Catalogue 133 3. Sources Co—incident with Optical Objects 155 VII THE VARIABLE SOURCES 160 VIII DISCUSSION 177 1. Completeness Level of the Survey 177 v i 2. General P r o p e r t i e s of the Compact Sources 180 2.1 Number-Flux Densi t y R e l a t i o n s h i p 181 2.2 D i s t r i b u t i o n i n G a l a c t i c Co-ordinates 186 2.3 The G a l a c t i c Component 191 3. The V a r i a b l e Sources 196 IX SUMMARY AND CONCLUSIONS 206 B i b l i o g r a p h y 210 Appendix 214 v i i LIST OF TABLES Table Page I Types of V a r i a b l e Radio Sources 12 II Summary of Survey Observations 33 III C a l i b r a t i o n Sources 37 IV E r r o r s on C a l i b r a t e d P o s i t i o n and Flux D e n s i t y 71 V Instrumental V a r i a t i o n s 113 VI The Catalogue of Compact Radio Sources 136 VII O p t i c a l P o s i t i o n C o — i n c i d e n c e s 158 VIII The V a r i a b l e Sources 164 IX P o s s i b l y V a r i a b l e Sources 165 LIST OF FIGURES Figure Pag 1. Schematic of the Telescope Receiver System 20 2. Sky Pattern of Survey Scans 23 3. The beam orientation and receiver response 25 4. Measurement of the raw receiver noise 28 5. Galactic latitude l i m i t s of the survey scans 32 6. D r i f t scans at 0° rotation through 3C 295 41 7. Comparison of beam models to measured p r o f i l e s 44 8. East-West beam model parameters in 1980 45 9. North-South beam model parameters in 1980 46 10. 1980 beam separations 47 11. Beam model parameters at 90° rotation angle 49 12. Relationship between north and south portion of the beams in 1978 and 1980 51 13. The 1980 to 1978 beam model conversion factors 52 14. Comparison of 1978 beam model to driven scan results . 53 15. The 1979 telescope pointing corrections 57 16. Conversion factors from 90° to 0° gain 58 17. The 1979 0° beam gains 59 18. The 1978 telescope pointing corrections 61 19. The 1978 0° beam gains 62 20. The ra t i o of 1979 to 1977 source strengths 64 21. The pointing difference between 1979 and 1977 65 22. Errors on the beam model as a function of x 67 23. Errors on the survey co-ordinates 72 i x 24. Beam—switched map of a h i g h l y confused reg ion 84 25. Beam—switched map of an unconfused reg ion 85 26. The rate of spurious s i g n a l d e t e c t i o n 88 27. Source d e t e c t i o n e f f i c i e n c y v s . S/N 96 28. S i m u l a t i o n r e s u l t s for measured scan p o s i t i o n 99 29. S i m u l a t i o n r e s u l t s for measured peak s t reng th 100 30. S i m u l a t i o n r e s u l t s for measured HPBW 101 31. Output s t r eng th versus input s t r e n g t h 104 32. F igure of M e r i t v s . S/N for i n s e r t s 105 33. F igure of M e r i t v s . S/N for unresolved sources 106 34. Amplitude d i s t r i b u t i o n of i n s t r u m e n t a l v a r i a t i o n s . . . . 1 1 4 35. The rms s i g n a l v a r i a t i o n s due to r e c e i v e r noise . . . . . . 1 1 7 36. Expected rms s i g n a l v a r i a t i o n v s . p—p d e f l e c t i o n 118 37. D i s t r i b u t i o n of short—term v a r i a b i l i t y i n d i c e s 120 38. D i s t r i b u t i o n of d e v i a t i o n s from I 0 124 39. I n t r i n s i c long—term f r a c t i o n a l s i g n a l v a r i a t i o n 125 40. D i s t r i b u t i o n of long—term v a r i a b i l i t y i n d i c e s 126 41. Scans through the v a r i a b l e GT0236 + 610 in 1977 161 42. Scans through the v a r i a b l e GT2134 + 536 in 1977 162 43. F lux d e n s i t y v s . time for short—term v a r i a b l e s 175 44. F lux d e n s i t y v s . time for short—term p o s s i b l e v a r i a b l e s 176 45. E f f e c t i v e scan width v s . f l u x d e n s i t y 179 46. Survey S o l i d Angle v s . F lux Dens i ty 182 47. Comparison to e x t r a g a l a c t i c source counts 184 48. G a l a c t i c l a t i t u d e d i s t r i b u t i o n of survey sources . . . . . 1 8 7 49. G a l a c t i c l ong i tude d i s t r i b u t i o n of survey sources . . . . 1 9 0 X 50. The d i s t r i b u t i o n of the r a t i o S m a x /S min f ° r v a r i a b l e and p o s s i b l e v a r i a b l e sources ....200 x i ACKNOWLEDGEMENTS F i r s t , and foremost, I would l i k e to thank my s u p e r v i s o r , Dr. P h i l l i p Gregory; h i s support made t h i s t h e s i s p o s s i b l e , and, h i s advice made i t a b e t t e r product than i t would otherwise have been. I a l s o thank the members of my Ph.D. committee f o r s t i m u l a t i n g feedback. D a r y l Pawluck and Mary—Ann P o t t s deserve thanks f o r t h e i r v a l u a b l e r o l e i n c r e a t i n g the soft—ware to d e a l with the vast q u a n t i t y of data produced by t h i s program. I must a l s o thank the s t a f f of NRAO fo r t h e i r support in c a r r y i n g out the ob e r v a t i o n s , and f o r e f f i c i e n t l y coping with the heavy demands t h i s p r o j e c t made on the t e l e s c o p e . F i n a l l y , I would l i k e to express my g r a t i t u d e to f r i e n d s , whose lon g — s t a n d i n g , support and encouragement were i n v a l u a b l e . 1 CHAPTER I INTRODUCTION The study of v a r i a t i o n s i s an important par t of research i n any f i e l d . V a r i a t i o n s r e f l e c t the dynamic aspects of p h y s i c a l processes , p r o v i d i n g an o b s e r v a t i o n a l l i n k to the f o r c e s , or c o n d i t i o n s , that a f f e c t departures from the e q u i l i b r i u m s t a t e . The i r study a i d s i n mapping out the r e l a t i o n s h i p s between observable p r o p e r t i e s that h i n t at the nature of the u n d e r l y i n g proces s . When i n t e r p r e t e d i n terms of changes in p h y s i c a l c o n d i t i o n s , the v a r i a t i o n s prov ide e f f e c t i v e t e s t s of t h e o r e t i c a l models. I t i s there fore not s u r p r i s i n g t h a t , h i s t o r i c a l l y , v a l u a b l e i n s i g h t s i n t o the nature of a s t r o p h y s i c a l phenomena have been obta ined through i n v e s t i g a t i o n s of v a r i a b i l i t y . Often the research y i e l d s r e s u l t s w i t h important a p p l i c a t i o n s i n other areas ; for example, the l u m i n o s i t y - p e r i o d r e l a t i o n s h i p of Cepheid v a r i a b l e s p rov ides a y a r d s t i c k for measuring e x t r a g a l a c t i c d i s t a n c e s . The study of v a r i a t i o n s i n the r a d i o emiss ion from a s t ronomica l sources i s s t i l l r e l a t i v e l y young; l e s s than twenty years o l d . While a great dea l i s known about the types of ob jec t s that e x h i b i t r a d i o v a r i a b i l i t y and the charac ter of the v a r i a t i o n s , the p i c t u r e i s l e s s than complete i n many r e s p e c t s . To ob ta in an understanding of the present s t a tus of the knowledge of v a r i a b l e r a d i o sources , i t i s worthwhile to b r i e f l y review the h i s t o r y of the i n v e s t i g a t i o n . 2 1. V a r i a b l e Radio Sources 1.1 E x t r a g a l a c t i c Evidence f o r v a r i a t i o n s i n the continuum r a d i o emission of e x t r a g a l a c t i c sources was f i r s t p r o vided by S h o l o m i t s k i i (1965), who measured a 30% change, at a wavelength of 32 cm, i n the f l u x d e n s i t y of the source CTA 102. S h o r t l y t h e r e a f t e r Dent (1965) rep o r t e d a 40% v a r i a t i o n s , over a three year p e r i o d , i n the centimeter continuum f l u x of the quasar 3C 273. These d i s c o v e r i e s motivated s e v e r a l observers to look f o r v a r i a b l i l i t y i n other r a d i o sources. As a r e s u l t , i n a review a r t i c l e a few years l a t e r , Kellermann and P a u l i n y - T o t h (1968) were able to l i s t 25 r a d i o v a r i a b l e s . For the most p a r t , the observed v a r i a t i o n s c o u l d be e x p l a i n e d v i a a simple model of an a d i a b a t i c a l l y expanding c l o u d of r e l a t i v i s t i c e l e c t r o n s (Kellermann 1966, van der Laan 1966), with o u t b u r s t s o c c u r r i n g at a frequency of about one per year. The temporal behaviour of the r a d i o emission t r a c e d out the e v o l u t i o n of the p h y s i c a l c o n d i t i o n s at the source, from the instantaneous i n j e c t i o n of e n e r g e t i c p a r t i c l e s and an i n i t i a l , o p t i c a l l y - t h i c k s t a t e , d u r i n g which time the f l u x d e n s i t y i n c r e a s e s , through to a l a t e r , o p t i c a l l y - t h i n s t a t e and decay in f l u x d e n s i t y . For cases where the simple model d e v i a t e d s i g n i f i c a n t l y from the o b s e r v a t i o n s , j u d i c i o u s manipulation of the model parameters (eg. continuous p a r t i c l e i n j e c t i o n , m u l t i p l e o u t b u r s t s or source components, e v o l v i n g magnetic f i e l d c o n f i g u r a t i o n s ) seemed adequate to e x p l a i n the o b s e r v a t i o n s . During the next decade, programs to r e g u l a r l y monitor the 3 flux densities of extragalactic sources were carr i e d out by a number of observers. Some of these surveys (eg. Andrew et a l . 1972; Medd et a l . 1972; Hobbs and Dent 1977; Andrew et a l . 1978 and Fanti et a l . 1980) were aimed at elucidating the nature of the variable sources and, hence, were confined to known, or suspected, variable sources, or to sources with properties thought to correlate with radio v a r i a b i l i t y , for example, compactness or f l a t spectrum. (Extended, o p t i c a l l y — t h i n , synchrotron sources show the canonical power law decay in flux density with increasing frequency.) Other surveys attempted to minimize selection bias and, thus, measure the incidence of v a r i a b i l i t y among extragalactic sources in general. Such surveys were carried out at frequencies of a few GHz by: Brandie 1972; Kesteven, Bridle and Brandie 1976; Brid l e , Kesteven and Brandie 1977; Kesteven, Bridle and Brandie 1977; Altschuler and Wardle 1977 and Webber et a l . 1980, and at sub-GHz frequencies by: Cotton 1976a; Cotton 1976b; Condon et a l . 1979; Fanti et a l . 1981 and Dennison et a l . 1981. The results of these surveys indicate that v i r t u a l l y a l l compact extragalactic sources ( s i g n i f i e d by continuum spectra that are f l a t or show an excess at higher frequncies) are variable at GHz frequencies and, at least, 40% to 50% are variables in the sub-GHz range. The incidence of v a r i a b i l i t y does not seem to correlate with any s p e c i f i c type of o p t i c a l object; implying a universal emission mechanism among these sources. The amplitudes of the variations are t y p i c a l l y a factor of 2, but may be as high as a factor of about 8. Observed v a r i a b i l i t y 4 time scales, in most cases, range from months to years. The exception is BL Lac type objects, for which s i g n i f i c a n t variations have been observed, in some sources, on a time scale of days. However, a number of the properties of the variable sources argue against the c l a s s i c a l expanding source model (Kellermann and Pauliny-Toth 1981). In general, the shape and frequency dependence of the outbursts does not conform to the simple van der Laan model, although again, reasonable agreement can be obtained through adjustment of the model parameters to suit individual cases. This limited success of the model indicates that expansion probably plays a major role in producing the observed variations, but some refinement of the simple model i s necessary. A major d i f f i c u l t y with the c l a s s i c a l model arises from the implied source diameters that are based on the n o n — r e l a t i v i s t i c causality argument, which l i m i t s emission that varies s i g n i f i c a n t l y on a time scale of r to regions with dimension less than C T . The large s i g n i f i c a n t f r a c t i o n a l , intensity variations at long wavelengths, when combined with the implied linear dimensions, indicate brightness temperatures of ~10 1 5 K (Hunstead 1972; Condon et a l . 1979; Dennison et a l . 1981). This is well above the upper l i m i t of 10 1 2 K imposed by inverse Compton losses (Kellermann and Pauliny-Toth 1969). Furthermore, the absence of i n t e r s t e l l a r s c i n t i l l a t i o n s among the low frequency variables (Dennison and Condon 1981), and the upper l i m i t on X-ray flux densities (Marsher et 5 a l . 1979), imply source dimensions that are well in excess of the l i g h t - t r a v e l time l i m i t . Thus, the observed v a r i a b i l i t y time scales implied that the e f f e c t s of processes occuring in these sources, travel with v e l o c i t i e s in excess of c. It has been suggested by a number of authors that the apparent superluminal variations of extragalactic sources can be explained by models incorporating r e l a t i v i s t i c motion of the radiating p a r t i c l e s . These models are supported by independent evidence for bulk r e l a t i v i s t i c motion in the form of superluminal structural changes detected via VLBI observations (Cohen et a l . 1977; and Pauliny-Toth et a l . 1981). Evidence for component separations, with apparent v e l o c i t i e s of up to about 45c, has been found. Current models for the variable sources involve anisotropic expansion, generally in the form of jets of r e l a t i v i s t i c electrons which have been suggested by the elongated radio structures seen both in the compact sources, on a scale of a few pc, and in the associated, extended emission, on a scale of Mpc's. For r e l a t i v i s t i c motion clo s e l y aligned with the di r e c t i o n to the observer, the f i n i t e speed of l i g h t causes an apparent time contraction with respect to the observers frame, resulting in the observed superluminal ef fects. While the r e l a t i v i s t i c models successfully remove the contradictions a r i s i n g from the c l a s s i c a l approach, a number of d i f f i c u l t i e s remain to be reconciled with the observations. Perhaps the most obvious problem arises from the fact that, in order to explain the superluminal variations, the d i r e c t i o n of 6 the r e l a t i v i s t i c j e t must be c l o s e l y a l i g n e d w i t h the d i r e c t i o n to the observer . Th i s makes i t d i f f i c u l t to e x p l a i n the observed h igh inc idence of v a r i a b i l i t y . Scheur and Readhead (1979) have suggested that t h i s s e l e c t i o n e f f e c t c o u l d e x p l a i n the ex i s t ence of r a d i o - q u i e t quasars ; however, t h i s i n t e r p r e t a t i o n a l s o encounters a number of d i f f i c u l t i e s . I t i s c l e a r t h a t , a l though much of t h e i r nature s t i l l remains a mystery, our understanding of e x t r a g a l a c t i c r ad io sources has been s u b s t a n t i a l l y improved through s t u d i e s of t h e i r v a r i a t i o n s . However, the observa t ions have e n t a i l e d c o n s i d e r a b l e b i a s . Before d i s c u s s i n g where the o b s e r v a t i o n a l d e f i c i e n c i e s l i e , i t i s best to complete the p i c t u r e of v a r i a b l e r ad io sources by c o n s i d e r i n g those that r e s ide i n our own ga l axy . 1.2 G a l a c t i c Although evidence for v a r i a b i l i t y from g a l a c t i c r a d i o sources , i n the form of a long-term decrease ( ~1% per year) in the f l u x d e n s i t y of the supernova remnant Cas A (Hogbom and Shakeshaft 1961), predates the d i s c o v e r y of Dent (1965), the present s ta te of the knowledge of g a l a c t i c v a r i a b l e s has not yet reached the w e l l organized and systemat ic s t a tus of e x t r a g a l a c t i c s t u d i e s . The major reason for t h i s i s t h a t , p r i o r to the l a t e 1960's , only those g a l a c t i c sources s t rong enough to be detected in the e a r l y , a l l sky , low frequency r a d i o surveys were known. These i n c l u d e d a number of s t rong thermal sources (HII reg ions) and a handful of s t rong non-7 thermal sources that were assumed to be either supernova remnants or background extragalactic sources. In 1969, Altenhoff et a l . carried out a survey of a large portion of the plane at 2.7 GHz, with a resolution of 11 arc-minutes and a minimum detection l i m i t of 2 Jansky ( 1 Jansky = 10" 2 6 Watts— nr 2—Hz~ 1). The survey revealed a few hundred discrete sources. Again, the majority of the sources were thermal and could be associated with HII regions (Mezger 1970). The non-thermal sources were taken to be supernova remnants (Downes 1971). In view of these associations, no attempts were made to monitor these sources for variations. With a few notable exceptions, the presently known galactic radio variables seldom reach flux density levels greater than a few hundred mJy and, therefore, had l i t t l e chance of being included in these early catalogues. With the exception of pulsars, discovered in 1968 (Hewish 1968) and for which systematic search techniques have been established, highly sensitive searches for discrete galactic sources of radio emission, and subsequently v a r i a b i l i t y , have taken the form of targeted surveys, or individual observations, of classes of objects suspected to be radio sources (either on the basis of previous detections from a member of the class or the known presence of a physical mechanism predicted to produce detectable emission). For example, in the late 1960's and the 1970's, such surveys were carr i e d out on: f l a r e stars (Lovell 1969) ; X-ray sources (Andrew and Purton 1968; Abies 1969; Hjellming and Wade 1971; Braes and Miley 1971, 1972); early 8 type s t a r s (Purton et a l . 1973, S i s t l a and Hong 1975, A l t e n h o f f et a l . 1976); symbiotic s t a r s (Gregory and Seaguist 1974, Gregory et a l . 1977); a combination of b i n a r y , v a r i a b l e and other p e c u l i a r s t a r s (Bath and W a l l e r s t e i n 1976); l a t e type s u p e r g i a n t s ( S m o l i n s k i , Feldman and Higgs 1977) and c l o s e b i n a r y s t a r s (Spangler, Owen and Hulse 1977). At present about 150 s t a r s are known sources of r a d i o emission (Wendker 1982). Other compact g a l a c t i c r a d i o sources i n c l u d e the HII regions and supernova remnants, p l a n e t a r y nebulae and p u l s a r s . Among the r a d i o s t a r s , two main c l a s s e s of. v a r i a b l e s e x i s t ; thermal sources, such as novae or emission from other forms of c i r c u m s t e l l a r matter, and non-thermal sources, v i r t u a l l y a l l of which are a s s o c i a t e d with known or suspected bi n a r y s t a r systems. The thermal sources have been observed to ' vary on a time s c a l e from months to years as a r e s u l t of e v o l u t i o n of the e j e c t e d c i r c u m s t e l l a r m a t e r i a l . V a r i a b l e r a d i o emission from the b i n a r y systems i s c h a r a c t e r i z e d by o u t b u r s t s l a s t i n g from a few hours to a few days. The non-thermal nature of the emission mechanism i s deduced from the t y p i c a l l y f l a t s p e c t r a of the r a d i a t i o n and the b r i g h t n e s s temperatures of 10 8 — 1 0 1 0 K i m p l i e d by the v a r i a b i l i t y time s c a l e s . In a l l cases, the r a d i a t i o n can be adequately e x p l a i n e d as synchrotron emission from r e l a t i v i s t i c e l e c t r o n s i n a magnetic f i e l d with s t r e n g t h , u s u a l l y , of the order of a few gauss. The strong c o r r e l a t i o n , between h i g h l y v a r i a b l e r a d i o emission and b i n a r y s t a r systems, has l e d some authors (eg. 9 Spangler, Owen and Hulse 1977) to suggest that the phenomenon of binarism plays an important role in providing the environment requisite to v a r i a b i l i t y . However, in spite of the fact that surveys for variable emission from other objects have been largely unsuccessful, i t i s not clear to what extent the co r r e l a t i o n results from selection bias. The binary systems exhibiting radio emission number s l i g h t l y more than twenty and are composed of three main groups. About half are RS CVn type binaries, distinguished by strong Call emission, a photometric d i s t o r t i o n wave that propagates slowly through the o p t i c a l l i g h t curve and a primary of spectral type F or G, with a s l i g h t l y l a ter companion. The remainder of the variables are either Algol type binaries, comprised of an early type primary and late type companion,and showing none of the p e c u l i a r i t i e s of the RS CVn's, or strong X—ray binaries. Only in the case of the RS CVn stars is the o r i g i n of the radio emission reasonably well understood. The RS CVn's are also weak X—ray sources (Walter, Charles and Bowyer 1978), and both the radio outbursts and the correlated X—ray emission are thought to arise from fl a r e s associated with chromospheric a c t i v i t y on the primary. This a c t i v i t y is linked to the giant "star spots" (cool photospheric regions) covering a large portion of the s t e l l a r surface, that have been invoked to explain the photometric d i s t o r t i o n wave. The RS CVn and Algol type binaries have similar radio properties. Typical radio luminosity, during outburst, i s 10 about 1 0 2 8 e r g s — s ~ 1 , with r a r e events reaching 1 0 2 9 e r g s — s _ 1 (Spangler, Owen and Hulse 1977; Feldman et a l . 1978). Outburst l u m i n o s i t i e s among the strong X—ray b i n a r i e s are much l a r g e r . In 1972, the X—ray b i n a r y Cyg X—3 experienced an outburst r e a c h i n g a l u m i n o s i t y of 1 0 3 5 e r g s - s " 1 (Gregory et a l . 1972). T h i s i s the most e n e r g e t i c outburst ever observed from a g a l a c t i c source. From the i n d i c a t e d source s i z e of 10 1 * cm (Gregory and Seaquist 1974), the volume e m i s s i v i t y of Cyg X-3, du r i n g o u t b u r s t s , was comparable to that of the intense compact e x t r a g a l a c t i c sources. In a d d i t i o n to r e v e a l i n g an unprecedented s c a l e of v a r i a b i l i t y , the d e t e c t i o n of the Cyg X—3 ou t b u r s t s underscored the p o s s i b i l i t y of a l i n k between t h i s c l a s s of g a l a c t i c v a r i a b l e and the compact e x t r a g a l a c t i c sources. Two other sources provide evidence that the p h y s i c a l mechanism(s) o c c u r r i n g i n the strong X—ray b i n a r i e s i s a s c a l e d down v e r s i o n of the proce s s ( e s ) r e s p o n s i b l e f o r the compact e x t r a g a l a c t i c v a r i a b l e s . Sco X—1 has a morphology that i s v i r t u a l l y i d e n t i c a l to the c l a s s i c a l e x t r a g a l a c t i c "double source"; a c e n t r a l compact and v a r i a b l e core, bracketed by two c o l i n e a r , n o n - v a r i a b l e steep spectrum sources (Geldzahler et a l . 1981). SS433 e x h i b i t s opposed, p r e c e s s i n g r a d i o and X-ray j e t s , composed of e n e r g e t i c e l e c t r o n s moving outward at a quarter of the speed of l i g h t . T h i s s c e n a r i o i s reminiscent of the bulk r e l a t i v i s t i c motions observed in a number of e x t r a g a l a c t i c sources, and the columated j e t s thought to be r e s p o n s i b l e f o r energy t r a n s p o r t to the elongated extended s t r u c t u r e s . These 11 s i m i l a r i t i e s suggest the p o s s i b i l i t y that the study of g a l a c t i c v a r i a b l e s can prov ide i n s i g h t s i n t o the mechanism that powers e x t r a g a l a c t i c sources . 2. O b s e r v a t i o n a l Short—comings Table I presents a summary of the known v a r i a b l e r a d i o sources . A rough i n d i c a t i o n (one s i g n i f i c a n t d i g i t ) of the number of known v a r i a b l e s of each type i s shown i n column 2. No attempt has been made to c a t e g o r i z e the e x t r a g a l a c t i c sources accord ing to o p t i c a l type , s i n c e , except for the shor ter v a r i a b i l i t y time sca le s for BL Lac o b j e c t s , no d i s t i n c t i o n i s ev ident i n t h e i r r a d i o p r o p e r t i e s . The observed v a r i a b i l i t y time sca le s are g iven i n the t h i r d column. Except i n the case of p u l s a r s , the v a r i a b l e source observa t ions over the past two decades which y i e l d the i n f o r m a t i o n i n t a b l e I have e n t a i l e d s i g n i f i c a n t s e l e c t i o n b i a s . For e x t r a g a l a c t i c sources , v a r i a b i l i t y has been determined by moni tor ing the f l u x d e n s i t y of sources l i s t e d i n r ad io source ca t a logues . Because these cata logues are the product of sky mapping surveys i n which a g iven p o r t i o n of the sky i s observed only once, sources that are s trong only a f r a c t i o n of the time are not l i k e l y to be i n c l u d e d . In a d d i t i o n , except for i n d i v i d u a l programs on a few sources , moni tor ing programs have been aimed at measuring long-term v a r i a t i o n s . The sample i n t e r v a l s of the observa t ions may be as low as a month, but are t y p i c a l l y of the order of a year . T h i s b ia s has been a r e s u l t of the genera l e x p e c t a t i o n Table I. Types of V a r i a b l e Radio Sources Type of Object Approximate Number Observed V a r i a b i l i t y Time Scale E x t r a g a l a c t i c : Quasars g a l a c t i c n u c l e i BL Lac o b j e c t s 200 months - years days - months Ga l a c t i c : P u l s a r s Thermal Sources Binary S t a r s 300 1 0 20 . 1 - 5 seconds months - years hours - days 1 3 t h a t , because of the d i s t a n c e s c a l e s i n v o l v e d , r a p i d v a r i a t i o n s would not be observed. However, i n l i g h t of the recent evidence for r e l a t i v i s t i c e f f e c t s i n a number of sources , very r a p i d v a r i a t i o n s cannot be r u l e d out on t h e o r e t i c a l grounds. Because of the s e l e c t i o n e f f e c t s mentioned; the r e s t r i c t i o n to e n t r i e s i n cata logues of "one shot " r ad io surveys and the long sample i n t e r v a l s of most moni to r ing programs, the ex i s t ence of very r a p i d v a r i a t i o n s , or of v a r i a b l e sources that are qu iescent a major f r a c t i o n of the t ime , i s an o b s e r v a t i o n a l ques t ion that has remained unanswered. Among g a l a c t i c sources , the data are even more incomplete . G a l a c t i c v a r i a b l e s are u n l i k e l y to be inc luded i n r a d i o source cata logues s i n c e , to the present day, no survey of a l a rge p o r t i o n of the g a l a c t i c plane has been c a r r i e d out w i t h s u f f i c i e n t s e n s i t i v i t y to detect the m a j o r i t y of known v a r i a b l e sources . Consequently , the d e t e c t i o n of g a l a c t i c v a r i a b l e sources has been dependent upon a p r i o r i assumptions about the type of ob ject expected to be v a r i a b l e . Furthermore, s ince these are u s u a l l y o p t i c a l o b j e c t s , d e t e c t i o n s have been l a r g e l y c o n s t r a i n e d to the o p t i c a l l y v i s i b l e p o r t i o n of the ga laxy , w i t h i n a few kpc of the s o l a r neighbourhood. The i n e f f i c i e n c y of t h i s technique i s i n d i c a t e d by the p a u c i t y of e n t r i e s i n t a b l e I . Improving the o b s e r v a t i o n a l s i t u a t i o n w i t h regard to g a l a c t i c v a r i a b l e s i s p a r t i c u l a r l y important i n view of the p o s s i b l e l i n k between some of the known v a r i a b l e s and compact e x t r a g a l a c t i c sources . A long s tanding gap i n our 1 4 understanding of these sources c e n t e r s around the mechanism r e s p o n s i b l e f o r generating the e n e r g e t i c p a r t i c l e s that give r i s e to the r a d i a t i o n . In g a i n i n g a b e t t e r understanding of these processes, g a l a c t i c v a r i a b l e s provide a number of d i s t i n c t o b s e r v a t i o n a l advantages over e x t r a g a l a c t i c sources. One obvious advantage i s t h e i r p r o x i m i t y . For t y p i c a l d i s t a n c e s i n the galaxy, the l i n e a r dimensions of g a l a c t i c v a r i a b l e s of l i g h t hours to l i g h t days, i n d i c a t e d by the v a r i a b i l i t y time s c a l e s , subtend angular diameters that are 10 — 10 3 times those t y p i c a l of the compact cores of e x t r a g a l a c t i c sources. Therefore s t r u c t u r a l changes that may be a s s o c i a t e d with the v a r i a t i o n s are more r e a d i l y mapped by VLBI a r r a y s . An a d d i t i o n a l advantage of p r o x i m i t y i s that c o s m o l o g i c a l e f f e c t s need not be c o n s i d e r e d . M o d e l l i n g of r a d i o o u t b u r s t s from e x t r a g a l a c t i c sources i s o f t e n confused by the s u p e r p o s i t i o n of a number of events. These m u l t i p l e events may a r i s e from the m u l t i p l e source components, which have a l s o been invoked to e x p l a i n the f l a t s p e c t r a observed from most compact sources. Outbursts from g a l a c t i c v a r i a b l e s are, on the other hand, u s u a l l y s i n g l e events. Thus the temporal behaviour of the ou t b u r s t s can be modelled i n i s o l a t i o n . F i n a l l y , the app a r e n t l y s h o r t e r v a r i a b i l i t y time s c a l e s of g a l a c t i c sources provide the convenience of a l l o w i n g data c o v e r i n g the e n t i r e e v o l u t i o n of an outburst to be obtained i n a short time span. C l e a r l y , i t i s important to i n c r e a s e the specimen base of g a l a c t i c v a r i a b l e s , and to do so i n as unbiased a f a s h i o n as p o s s i b l e . T h i s t h e s i s d e s c r i b e s a new, s e n s i t i v e survey f o r 15 h i g h l y v a r i a b l e r a d i o emission that addresses the b i a s e s inherent i n previous o b s e r v a t i o n s . The search f o r v a r i a b i l i t y i s c a r r i e d out by making repeated 6 cm maps of the northern g a l a c t i c plane, and examining the data f o r evidence of v a r i a t i o n s on time s c a l e s of a few days and one or two years. Thus the ob s e r v a t i o n s are not l i m i t e d to p r e v i o u s l y catalogued sources, nor have any assumptions been made about the types of sources expected to be v a r i a b l e . Since the g a l a c t i c plane i s tra n s p a r e n t to centimeter wavelength r a d i a t i o n , the ob s e r v a t i o n s cover both g a l a c t i c and e x t r a g a l a c t i c r a d i o emission. The survey i s capable of d e t e c t i n g v a r i a b i l i t y at a minimum l e v e l of about 40 mJy. In a d d i t i o n , the combined survey o b s e r v a t i o n s provide a new catalogue of compact r a d i o sources in the g a l a c t i c plane to a minimum f l u x d e n s i t y of about 20 mJy; about one order of magnitude more s e n s i t i v e than any p r e v i o u s l y a v a i l a b l e c a t a l o g u e s . 16 CHAPTER II THE SURVEY 1. Instrumentation There are a few b a s i c c o n s i d e r a t i o n s which a f f e c t the cho i c e of the instrument used to c a r r y out the survey. F i r s t , a high s e n s i t i v i t y i s r e q u i r e d . Although o u t b u r s t s s i m i l a r to those e x h i b i t e d by Cyg X-3 are r e a d i l y d e t e c t a b l e anywhere i n the galaxy with most r a d i o t e l e s c o p e s , the m a j o r i t y of known g a l a c t i c v a r i a b l e s have l u m i n o s i t i e s which, at t y p i c a l d i s t a n c e s i n our galaxy, produce f l u x d e n s i t i e s of 10's of mJy or l e s s . A c h i e v i n g t h i s s e n s i t i v i t y , with an i n t e g r a t i o n time per beam area small enough to allow o b s e r v a t i o n of a l a r g e p o r t i o n of the g a l a c t i c plane on a time s c a l e of days, r e q u i r e s the combination of a l a r g e c o l l e c t i n g area and a low noise r e c e i v e r . The choice of observing frequency f o r the survey i s a l s o important, and i s a f f e c t e d by two f a c t o r s . At long wavelengths, synchrotron sources that are compact, and thus l i k e l y to vary on short time s c a l e s , are s e l f — a b s o r b e d . T h e r e f o r e , the f l u x d e n s i t i e s are higher at s h o r t e r wavelengths. On the other hand, at wavelengths s h o r t e r than a few centimeters atmospheric i n s t a b i l i t i e s , which produce v a r i a b l e atmospheric emission, become important, and can s e v e r l y degrade the s e n s i t i v i t y of a survey. Another major c o n s i d e r a t i o n , which i s r e l a t e d to the s e n s i t i v i t y of the survey, i s the l e v e l of the con f u s i o n 17 s i g n a l . In the g a l a c t i c p l ane , confus ion a r i s e s both from the background of unresolved e x t r a g a l a c t i c r a d i o sources and from the r a d i o emiss ion a s soc i a t ed w i t h g a l a c t i c o b j e c t s , such as complexes of HII reg ions or the f i l a m e n t a r y s t r u c t u r e of supernova remnants. To f i r s t o rder , i n a survey for v a r i a b i l i t y , a constant confus ion background can be i g n o r e d . However, in regions where the confus ion s i g n a l i s s t rong and h i g h l y s t r u c t u r e d , v a r i a t i o n s i n the te le scope p o i n t i n g can r e s u l t i n a v a r i a b l e confus ion background. To over—come t h i s e f f e c t , the p o i n t i n g of the te le scope must be s t a b l e to w i t h i n a smal l f r a c t i o n of the antenna beam—width. In a d d i t i o n , the noise—like nature of the confus ion s i g n a l a f f e c t s the lower l i m i t for source d e t e c t i o n and reduces the accuracy of d e r i v e d source s t rengths and p o s i t i o n s . The c o n t r i b u t i o n to the confus ion s i g n a l from the e x t r a g a l a c t i c source background decreases r a p i d l y w i t h the antenna beam a rea . However, a beam s i z e that reduces the confus ion l e v e l to much l e s s than the noise s e n s i t i v i t y l i m i t , u n n e c e s s a r i l y increases the observ ing time r e q u i r e d to cover a g iven reg ion of the sky . The optimum beam s i z e y i e l d s a confus ion l e v e l only s l i g h t l y l e s s than the r e c e i v e r noise l e v e l . I f we de f ine the confus ion l e v e l as the f l u x d e n s i t y (S) at which the number d e n s i t y of e x t r a g a l a c t i c sources equals one per beam a rea , then , for a source number d e n s i t y g iven by N(S)=N 0S" o i, the beam diameter r e q u i r e d to reduce the confus ion l e v e l to C i s (C/N 0) . For a s i m p l e , i s o t r o p i c Euc l idean u n i v e r s e , the number d e n s i t y at 6 cm i s approximate ly given by No=60 and a=1.5 (Kellermann and 18 P a u l i n y - T o t h 1979). With these v a l u e s , a c o n f u s i o n l e v e l of a few mJy r e q u i r e s a beam diameter of a few arc-minutes. Confusion from the extended s t r u c t u r e i n the g a l a c t i c plane can be g r e a t l y reduced by employing a beam—switched radiometer with c l o s e l y spaced beams. T o t a l i n t e n s i t y maps of the inner 60° of the g a l a c t i c plane at 6 cm, with r e s o l u t i o n of 3', have been produced by A l t e n h o f f et a l . (1978). These maps show a number of s t r u c t u r e s with t y p i c a l angular dimensions of the order of 1° and i n t e g r a t e d f l u x d e n s i t i e s of tens of Jansky. A beam—switched system has a w e l l d e f i n e d response to a compact source, but l a r g e l y f i l t e r s out s t r u c t u r e with s p a c i a l f r e q u e n c i e s much l e s s than the inv e r s e of the beam s e p a r a t i o n . Beam—switching a l s o g r e a t l y reduces the e f f e c t s of atmospheric emission; v a r i a b l e atmospheric emission on time s c a l e s g r e a t e r than the switc h i n g r a t e are f i l t e r e d out. In summary, the instrument chosen f o r the survey o b s e r v a t i o n s must s a t i s f y the f o l l o w i n g requirements: 1) high s e n s i t i v i t y (a few mJy) i n a reasonable i n t e g r a t i o n time, t h e r e f o r e a l a r g e c o l l e c t i n g area and low noise r e c e i v e r ; 2) e x t r a g a l a c t i c c o n f u s i o n l e v e l < noise l e v e l , t h e r e f o r e a beam s i z e of a few arc—minutes; 3) p o i n t i n g s t a b i l i t y to w i t h i n a small f r a c t i o n of a beam—width; 4) c a p a b i l i t y of o p e r a t i n g at short (centimeter) wavelengths, and, f i n a l l y , 5) a beam—switched radiometer to reduce the e f f e c t s of g a l a c t i c c o n f u s i o n s t r u c t u r e and atmospheric i n s t a b i l i t i e s . With these c o n s i d e r a t i o n s i n mind, the instrument chosen for the survey was the 91 meter t r a n s i t t e l e s c o p e of the 19 N a t i o n a l Radio Astronomy Observatory (NRAO) at Green Bank, W . V i r g i n i a . The te l e s c o p e was operated at the antenna short wavelength l i m i t of 6 cm. Two feeds, both s e n s i t i v e to l e f t — h a n d c i r c u l a r l y p o l a r i z e d r a d i a t i o n , are mounted at the prime focus of the antenna. Each feed produces a beam with half—power beam width (HPBW) of about 3 arc-minutes. The beams are separated by about 7 arc-minutes about the symmetry a x i s of the antenna. The feed mount i s r o t a t a b l e , a l l o w i n g c o n t r o l of the o r i e n t a t i o n of the l i n e j o i n i n g the two beams with respect to the meridian. The p o i n t i n g of the te l e s c o p e i s s t a b l e , from day to day, to wi t h i n 10"—20" r or about 5% of the HPBW. The t e l e s c o p e s e n s i t i v i t y i s a maximum, when p o i n t i n g at the z e n i t h , of about 1 K/Jy. However, the s e n s i t i v i t y , the beam widths and the beam s e p a r a t i o n are a l l f u n c t i o n s of the e l e v a t i o n of the t e l e s c o p e , with c o n s i d e r a b l e d i s t o r t i o n of the beams and degradation in the s e n s i t i v i t y o c c u r r i n g at z e n i t h angles >, 40°. The operable d e c l i n a t i o n range of the t e l e s c o p e i s approximately 0°<6<80°. Within t h i s range, the beams are we l l behaved. Scans through strong sources show a s i n g l e s i d e — l o b e , at a l e v e l of -15 db, s i t u a t e d 5 arc—minutes west of each beam (see f i g u r e 6). No s i d e — l o b e s are e v i d e n t , down to -30 db, wit h i n g one degree north or south of the beams. Fi g u r e 1. shows a schematic diagram of the t e l e s c o p e r e c e i v e r system. The two feeds l a b e l e d A and B in the diagram are each connected to two cooled, parametric a m p l i f i e r r e c e i v e r s . Each r e c e i v e r has a t o t a l system temperature of 68 K and a 3 db i . f . bandwidth of 580 MHz, extending from 4.5 to TO SNITCH DRIVE OSCILLATOR Noise Cal Noise Cal COLD LOAD TO FRONT END SNITCHES I 2 3 • • • "A" PARAMP TRANSISTOR AMPLIFIER 4.5 to 5.1 O i l FILTER MIXER LEVEL PUMP L. 0. AMP COLD LOAD 1 2 3 • • • "B" PARAMP LEVEL PUMP L. 0. TRANSISTOR AMPLIFIER 4.5 to 5.1 GHt FILTER IF AMP SQ. LAN DETECTOR — r ~ SYNC. DETECTOR L0N PASS FILTER "A" out MIXER IF AMP SQ. UN DETECTOR SNITCH DRIVE OSCILLATOR SYNC. DETECTOR LON PASS FILTER "B" out Figure 1. Schematic of the telescope receiver system. 21 to 5.1 GHz. The inputs of each receiver are switched between the two feeds at a rate of 50 Hz. The switches are operated in anti-phase so that, when receiver 1 i s connected to feed A, receiver 2 i s connected to feed B. Each receiver thus yi e l d s tan independent measure of the d i f f e r e n t i a l output of the two feeds. This is a valuable asset for the confirmation of transient emission. In addition, when the receiver outputs are combined, an improvement in the receiver noise l e v e l by a factor of 72" is obtained. 2. Observat ions 2.1 Method The basic observational unit of the survey i s a scan, c a r r i e d out by recording the output of the two receivers while driving the telescope at a fixed rate along the meridian. The telescope motion, feed orientation and data acquisition are controlled by computer. The epoch 1950 start and stop time, the 1950 start declination and the driving rate for each scan are read by the computer from cards that are prepared prior to each observing session. The computer precesses the start co-ordinates for each scan to the present epoch and computes a track for the telescope so that, at the l o c a l sidereal time of the start of the scan, i t reaches the start declination moving at the f u l l commanded rate. Data i s recorded u n t i l the precessed stop time is reached. The commanded rate is not precessed. Therefore, the rate in the 1950 co-ordinate system varies along the scan. The magnitude of t h i s effect depends on 22 the r a t e of change of the p r e c e s s i o n constants along the scan, and i s l a r g e s t at high d e c l i n a t i o n . At the h i g h e s t d e c l i n a t i o n of the survey (6=62°), the d i f f e r e n c e between the epoch and 1950 r a t e i s about 10%. The e f f e c t of t h i s d i f f e r e n c e on observed source c o - o r d i n a t e s i s removed, to an accuracy of a few arc—seconds, by i n t e r p o l a t i o n (see s e c t i o n IV 3.3). For the survey o b s e r v a t i o n s , the t e l e s c o p e i s d r i v e n at a r a t e of 130'/min, c l o s e to the maximum a d j u s t a b l e servo r a t e of the t e l e s c o p e d r i v e motors. Each scan i s 2 minutes in d u r a t i o n , or 4.3 degrees in l e n g t h , and the s t a r t c o - o r d i n a t e s are c a l c u l a t e d to center the scan on the g a l a c t i c plane (b=0°). To o b t a i n e x t e n s i v e coverage of the g a l a c t i c plane, a sequence of a l t e r n a t i n g northbound (NB) and southbound (SB) scans i s executed, producing a z i g - z a g p a t t e r n of scans c e n t e r e d on the g a l a c t i c plane. A sample of the p a t t e r n of a scan sequence for a small p o r t i o n of the survey r e g i o n i s shown in f i g u r e 2. As a r e s u l t of e a r t h r o t a t i o n , the scans are i n c l i n e d 3° to 6° from a great c i r c l e of constant r i g h t a s c e n s i o n , and adjacent scans are separated by about 2 20 . A f t e r each NB scan, the t e l e s c o p e i s h e l d s t a t i o n a r y f o r 12 seconds. A s t a b l e noise tube i s f i r e d at the f r o n t end of the r e c e i v e r s f o r h a l f of t h i s time i n t e r v a l , to provide a measure of the r e c e i v e r g a i n s . These c a l i b r a t i o n scans are i n d i c a t e d by the short h o r i z o n t a l bars in the diagram. Since the t e l e s c o p e i s a t r a n s i t instrument, only a s i n g l e sequence of scans can be c a r r i e d out i n one day, and i t i s obvious from f i g u r e 2. that one sequence c o n s i d e r a b l y 23 T 1 r T 1 1 1 1 1 1 1 r 5 3 5 2 5 1 5 0 o 491 o c u a 48 47 4 6 Telescope Beams _ i 20 18 16 14 Right Ascension (minutes) 2 0 h ! 0 m Fiqure 2. Sky pattern of the survey scans. The so l i d l ines show the track of the telescope for a sample of one sequence of observations. Scans are a l ternate ly north and south bound and centered on the ga lact ic plane (dashed l i n e ) . The short horizontal bars are receiver ca l i b ra t i on scans. 24 undersamples the plane i n the RA d i r e c t i o n . Greater coverage i s obtained by i n t e r l e a v i n g a number of scan sequences. Each sequence i s separated by 19 sec of time. The angular s e p a r a t i o n i s thus, a f u n c t i o n of d e c l i n a t i o n , being 4.8 arc—minutes at 6=0° and 2.4 arc—minutes at 6=60°. V a r i a b i l i t y on a time s c a l e of a few days i s measured by executing each sequence a number of times during each observing s e s s i o n . In a d d i t i o n , each sequence i s observed d u r i n g two observing s e s s i o n s , separated by about one year, to measure y e a r l y v a r i a t i o n s . The r a t i o of the HPBW's of the beams to the s e p a r a t i o n of scans i n adjacent sequences i s such that strong sources w i l l appear in two or more scans, but weaker sources may produce d e t e c t a b l e s i g n a l s i n only the nearest scan. For t h i s reason, and because the s i g n a l s produced by a v a r i a b l e source i n adjacent scans on d i f f e r e n t days cannot be used to determine the source p o s i t i o n , the i n f o r m a t i o n r e q u i r e d to c a l c u l a t e the p o s i t i o n and f l u x d e n s i t y of a source must be obtained from the data i n a s i n g l e scan through the v i c i n i t y of the source. T h e r e f o r e , during a scan, the r o t a t i o n angle of the feed box i s set so that the beams are o f f s e t to each s i d e of the c e n t r a l scan t r a c k . T h i s c o n f i g u r a t i o n i s i l l u s t r a t e d f o r a NB scan in f i g u r e 3. The angle of 11°, between the l i n e j o i n i n g the two beams and the scan t r a c k , produces a beam s e p a r a t i o n orthogonal to the track of about 1/2 of a HPBW. With the beams o r i e n t e d in t h i s manner, the r a t i o of the p o s i t i v e and negative s i g n a l s produced by scanning through a source i s a unique f u n c t i o n of 25 Figure 3. The beam or ientat ion with respect to the central track (track 2) i s shown for a northbound scan. The boxes indicate the receiver response produced by a radio source s ituated on tracks 1, 2 or 3. 26 the o f f s e t of the source from the c e n t r a l t r a c k . From a knowledge of the beam p r o f i l e s , t h i s o f f s e t , and subsequently the s t r e n g t h of the source normal ized to the beam peaks, can be determined. The increase i n the e f f e c t i v e width of the scan by about 5 0 % , over a scan w i t h the beams a l i g n e d , i s an a d d i t i o n a l advantage of t h i s t echnique . At a scanning rate of 1 3 0 ' / n u n and a beam width of 3', the i n s t r u m e n t a l response of one beam to a po in t source has a h a l f -power width of 1.4 seconds of t i m e . The f o u r i e r t rans form of the response i s approximate ly gaussian w i t h s tandard d e v i a t i o n of 0.27 Hz, and, thus , 9 9 % of the s i g n a l i s represented by f o u r i e r components at f requencies l e s s than i / c = 3 c r v = 0 . 8 Hz . The p o i n t source response i s , t h e r e f o r e , f u l l y sampled at the Nyquis t frequency (2vc) of 1 *. 6 Hz ; corresponding to a sample i n t e r v a l of 0.6 sec . However, i n order to d i s t i n g u i s h impulse type s i g n a l , such as i n t e r f e r e n c e or pul sed e x t r a t e r r e s t i a l e m i s s i o n , from the slower source response, the p o s t - d e t e c t i o n low pass f i l t e r (see f i g . 1) has a 3 db bandwidth extended to 2.5 Hz . To prevent a l i a s i n g of the higher frequency components of t h i s pass band, and to adequately sample impulse s i g n a l s when they occur , the sample frequency i s increased to twice the low pass bandwidth by sampling the r e c e i v e r output every 0.2 seconds. The t h e o r e t i c a l rms noise i n the raw r e c e i v e r outputs i s g iven by equat ion I I . 1 ( T u i r i , 1 9 6 6 ) ATrms=K-Tsys / V / A I Z - A T (11.1) where Av i s the h igh frequency p r e - d e t e c t i o n band width and A T 27 i s the post—detect ion i n t e g r a t i o n t i m e . S i n c e , for a switched r e c e i v e r system the output i s the d i f f e r e n c e between two input l e v e l s and the e f f e c t i v e i n t e g r a t i o n time i s reduced by 1/2, the constant K i n equat ion I I . 1 has a va lue of 2. For T S y S = 68 K, Ai/=580 MHz and, f o l l o w i n g T u i r i (1966), A T = 0 .13 , the t h e o r e t i c a l raw r e c e i v e r noise l e v e l i n a s i n g l e scan i s 16 mK. Thi s i s in good agreement w i t h the measured value of A T r m s (see f i g u r e 4 ) , w i t h the exceptio'n of r e c e i v e r 2 i n 1979 for which the noise l e v e l i s much h i g h e r . The noise l e v e l i n t h i s r e c e i v e r i s such that no ga in i s obta ined by combining the r e c e i v e r ou tput s . Thus, for 1979, on ly the output of r e c e i v e r 1 i s ana ly sed . For 1977 and 1978, combining the r e c e i v e r outputs reduces the raw noise l e v e l by a f a c t o r of J2 to 11.3 mK. A l a rge f r a c t i o n of the raw r e c e i v e r noise occurs at f requencies much l a r g e r than the h ighes t frequency components of the in s t rumenta l response. The high frequency noise power i s removed by d i g i t a l f i l t e r i n g of the data as par t of the a n a l y s i s . As a r e s u l t , for the purpose of source d e t e c t i o n , the e f f e c t i v e r e c e i v e r noise i s much lower than the raw l e v e l . The noise l e v e l in a s i n g l e scan, a f t e r f i l t e r i n g , i s 5.9 mK for one r e c e i v e r and 4.2 mK for combined r e c e i v e r s . A sample i n t e r v a l of 0.2 sec produces about 600 data samples per scan from each r e c e i v e r . Thus, a s i n g l e days observa t ion of one sequence, which conta ins about 300 scans, produces about 4x10 5 data samples. These da ta , as w e l l as the r e s u l t s of the noise tube c a l i b r a t i o n s , are w r i t t e n d i r e c t l y 28 1979 200 ^ 0"= 15.3 mk 100 -CM— l e 1978 once 200 -cr= 15.3 mk > Scan 100 l i 1977 200 -^ 0"= 16.7 mk too I > l/n Figure 4. Measurement of the raw receiver noise. The noise power i s given by the change in the variance of the scan data with the number of observations averaged. The data shown are from the output of receiver one in each observing session. 29 onto magnetic tape at the t e l e s c o p e s i t e . Along with the r e c e i v e r outputs, a header i s w r i t t e n f o r each scan c o n t a i n i n g the scan and r e c e i v e r i d e n t i f i e r s , the p o s i t i o n of the t e l e s c o p e d u r i n g the scan and the d r i v e r a t e , c a l c u l a t e d from the change i n the observed p o s i t i o n per data sample. At the end of each observing s e s s i o n , the data on the t e l e s c o p e tapes are run through p r e l i m i n a r y p r o c e s s i n g at the NRAO computing c e n t r e i n C h a r l o t t e s v i l l e , V i r g i n i a . At t h i s stage, the r e s u l t s of the noise tube c a l i b r a t i o n s are a p p l i e d to the r e c e i v e r outputs, to convert the data to a measure of the antenna temperature. The c a l i b r a t e d data are then shipped to the U n i v e r s i t y of B r i t i s h Columbia fo r f i n a l a n a l y s i s . In a d d i t i o n to the d i g i t a l data, the r e c e i v e r outputs are monitored in r e a l time v i a s t r i p c h a r t r e c o r d i n g s . These records provide a quick check on the q u a l i t y of the data. Scans that are unusable due to i n t e r f e r e n c e , bad weather or f a u l t y o p e r a t i o n of the t e l e s c o p e are noted at t h i s stage and f l a g g e d f o r e d i t i n g . 2.2 Coverage The survey region i s that p o r t i o n of the g a l a c t i c plane w i t h i n the operable d e c l i n a t i o n range of the t e l e s c o p e . T h i s i n c l u d e s the e n t i r e northern h a l f of the plane (6>0°), corresponding to the 180° l o n g i t u d e range of 40°<1<220°. Within t h i s l o n g i t u d e i n t e r v a l , the l a t i t u d e coverage v a r i e s with the i n c l i n a t i o n of the plane (b=0°) to the t e l e s c o p e meridian. At the most northern extreme (6=62°), where dl/d6=0, 30 the l a t i t u d e range i s equal to the scan l e n g t h (± 2.1°). Away from t h i s r e g i o n , the range decreases to a minimum of ± 1.2°. The l a t i t u d e coverage as a f u n c t i o n of l o n g i t u d e i s p l o t t e d f o r both NB and SB scans i n f i g u r e 5. F u l l coverage of the plane w i t h i n these boundaries i s obtained with 14 i n t e r l e a v e d scan sequences. Observations of a l l 14 sequences were completed in October 1981. The NB and SB scans, s e p a r a t e l y , y i e l d two complete surveys of the plane. T h i s t h e s i s presents the a n a l y s i s of o b s e r v a t i o n s of the f i r s t f i v e scan sequences c a r r i e d out duri n g August of 1977,1978 and 1979. The o b s e r v a t i o n s cover a t o t a l s o l i d angle of 0.09 s t e r a d i a n s . Table II giv e s a summary of the o b s e r v a t i o n s f o r each of these three observing s e s s i o n s . The f i r s t o b s erving s e s s i o n , in 1977, was a p i l o t study to assess the f e a s i b i l i t y of the survey. The e n t i r e observing s e s s i o n was devoted to sequence one, and the o b s e r v a t i o n s covered the smaller l o n g i t u d e i n t e r v a l 40°<1<150°. Based on the success of the 1977 o b s e r v a t i o n s , the survey region was expanded to the e n t i r e northern g a l a c t i c plane and o b s e r v a t i o n s of sequences 1 to 5 were c a r r i e d out i n 1978 and 1979. Each sequence has been executed at l e a s t 6 times during one observing s e s s i o n and at l e a s t 8 times in t o t a l . The a c t u a l number of o b s e r v a t i o n , per sequence may be l e s s than i n d i c a t e d i n the t a b l e f o r some p o r t i o n s of the survey area due to e d i t i n g of the data (see s e c t i o n IV 2.). In a d d i t i o n , the l e v e l of g a l a c t i c c o n f u s i o n w i t h i n the l o n g i t u d e regions 40°<1<55°, 78°<1<86° and 31 111°<1<114° i s so l a r g e that these areas are, i n e f f e c t , not covered by the a n a l y s i s of the data (see s e c t i o n IV 3.2) 32 Figure 5. The ga lact i c la t i tude l im i t s of the survey observations. The s o l i d l i ne shows the l im i t s fo r northbound scans, and the dashed l i ne for southbound scans. 33 Table I I . Summary of the Survey Observations DATE No. of Observations per Sequence Seq 1 Seq 2 Seq 3 Seq 4 Seq 5 Longitude Range Aug 1977 Aug 1978 Aug 1979 20 5 8 7 2 2 2 4 5 6 6 40°< 1 <150° 40°< 1 <220° 40°< 1 <220° T o t a l =27 12 12 8 8 34 CHAPTER III CALIBRATIONS 1 . I n t r o d u c t i o n In going from the raw scan data, i n the form of antenna temperature as a f u n c t i o n of t e l e s c o p e p o s i t i o n , to a l i s t of r a d i o sources with measured f l u x d e n s i t y and c e l e s t i a l co-o r d i n a t e s three processes are i n v o l v e d ; 1) d e t e c t i o n and r e c o g n i t i o n of the source s i g n a l , 2) measurement of the s i g n a l s t r e n g t h and p o s i t i o n , and 3) co n v e r s i o n of the measurements to c o n v e n t i o n a l u n i t s . C a r r y i n g out these processes r e q u i r e s knowledge of a number of t e l e s c o p e parameters. The s i g n a t u r e of an unresolved source i n a scan i s given by the North-South c r o s s - s e c t i o n of the instr u m e n t a l p r o f i l e . From the r a t i o of the p o s i t i v e and negative peaks of the source p r o f i l e the source s t r e n g t h and p o s i t i o n , r e l a t i v e to the c e n t r a l scan t r a c k , i s c a l c u l a t e d (see f i g u r e 3.). For t h i s c a l c u l a t i o n the East-West c r o s s s e c t i o n of the beam p r o f i l e s must be known. F i n a l l y , to convert the source s t r e n g t h s to absolute f l u x d e n s i t y and to c o r r e c t the observed p o s i t i o n s f o r systematic p o i n t i n g e r r o r s , the peak beam gains and t e l e s c o p e p o i n t i n g e r r o r s must be measured. T h i s chapter d e s c r i b e s the c a l i b r a t i o n s c a r r i e d out to determine these p r o p e r t i e s . A l l of these q u a n t i t i e s , the beam p r o f i l e s , peak gains, and p o i n t i n g e r r o r s are d e c l i n a t i o n dependent; p r i m a r i l y as a r e s u l t of changes i n the g r a v i t a t i o n a l d i s t o r t i o n of the antenna with z e n i t h angle. Therefore i t i s necessary to o b t a i n 35 c a l i b r a t i o n measurements c o v e r i n g the e n t i r e 0 to 65 degree d e c l i n a t i o n range of the survey o b s e r v a t i o n s . Since the te l e s c o p e time scheduled f o r the survey i s l i m i t e d , a major c o n s i d e r a t i o n when planning c a l i b r a t i o n s i s the observing time r e q u i r e d . The c a l i b r a t i o n r e q u i r i n g the g r e a t e s t amount of obs e r v i n g time i s the measurement of the East-West beam p r o f i l e , which, i n order to reproduce the c o n d i t i o n s d u r i n g survey o b s e r v a t i o n s (see f i g u r e 3), should be c a r r i e d out with the feed box at near zero degrees r o t a t i o n angle (the feed box r o t a t i o n angle i s measured clo c k w i s e from the meridian, with zero degrees corresponding to North — South alignment of the beams with beam A i n the North). Because the te l e s c o p e i s a t r a n s i t instrument, three days are r e q u i r e d to ob t a i n these p r o f i l e s ; one to measure the beam s e p a r a t i o n s and two more to execute scans through each of the beams at zero degrees r o t a t i o n . For 1977 to 1979 observing s e s s i o n s , the assumption was adopted that the p r o p e r t i e s of the beams are independent of the r o t a t i o n angle of the feed box. With t h i s approximation a s i n g l e d r i f t scan, with the beams a l i g n e d p e r p e n d i c u l a r to the meridian (90° r o t a t i o n angle) y i e l d s , s i m u l t a n e o u s l y , the r i g h t ascension p o i n t i n g e r r o r s , the beam s e p a r a t i o n , the r i g h t a s c e n s i o n (East—West) beam p r o f i l e s , and the peak beam gains. The North-South beam p r o f i l e s are obtained by scanning through a source at a high d e c l i n a t i o n r a t e with the beams a l i g n e d along the scan t r a c k . C a l i b r a t i o n s f o r the 1977 to 1979 observing s e s s i o n s were c a r r i e d out in t h i s manner. However, duri n g the f o u r t h 36 observing session, in August 1980 the 0° East-West beam p r o f i l e s were measured d i r e c t l y . Comparision of the beams at 0° and 90° feed box rotation angle showed both a substantial difference in the p r o f i l e s , and a change in the peak gains of up to 20%. Although the measurement of short-term v a r i a b i l i t y is not affected by an incorrect beam p r o f i l e , the calculated, absolute flux density and position of a source are strongly dependent on the shape of the beams. The magnitude of the difference between the 0° and 90° beams i s such that s i g n i f i c a n t inprovement in the accuracy of the 1977 to 1979 results can be obtained by correcting for the rotation angle dependence. For this reason, much of this chapter discusses the 1980 c a l i b r a t i o n measurements and their application to the 77 to 79 observations. The radio sources used to c a l i b r a t e the telescope were extracted from a l i s t of c a l i b r a t i o n standards, compiled for this purpose by Dr. P. Crane of NRAO. A subset of this l i s t , that was found to be flux stable during the 2.7 GHz monitoring program of Kesteven et a l . (1976) and Bridle et a l . (1977), was used for gain c a l i b r a t i o n . Flux densities at 5 GHz are on the scale of Pauliny—Toth and Kellermann (1968). Source co-ordinates, which originate from various authors, are t y p i c a l l y interferometer measurements and known to a few arc-seconds, or better. Table III l i s t s the c a l i b r a t i o n sources used, including, for each source, the assumed co-ordinates and 5.0 GHz flux density. 37 Table I I I . Calibr a t i o n Sources Source R.A h . (1950) m s DEC 0 (1950) i it Flux Density (Jansky) 3CR 27 00 52 44.90 68 06 06.0 2.48 + .06 3C 48 01 34 49.80 32 54 20.7 5.37 + .07 3C 52 01 45 14.90 53 1 7 46.0 1 .48 + .06 3C 131 04 50 10.55 31 24 31.7 0.86 + .04 3C 142.1 05 28 48.00 06 28 16.0 1 .02 + .04 3C 165 06 40 04.90 23 22 08.0 0.77 + .03 3C 181 07 25 20.31 1 4 43 46.6 0.66 + .05 0742+103 07 42 48.46 10. 18 32.9 • 3.84 + .07 3C 190 07 58 45.13 1 4 23 02.2 0.82 + .06 3C 196 08 09 59.42 48 22 07.2 4.36 + .06 3C 197.1 08 18 01.11 47 1 2 11.0 0.86 + .06 DA 251 08 31 04.38 55 44 41.6 5.60 + .06 3C 208 08 50 22.98 1 4 04 18.9 0.54 + .05 3C 213.1 08 58 05.16 29 13 33.2 0.84 + .03 3C 217 09 05 41.14 38 00 29.6 0.48 + .06 3C 216 09 06 17.34 43 05 59.2 1.81 + .04 DA 267 09 23 55.29 39 1 5 24.3 7.57 + . 1 3 3C 236 1 0 03 05.39 35 08 48. 1 1 . 34 + .08 1 039 + 029 1 0 39 04. 18 02 58 14.7 0.99 + .06 3C 247 10 56 08.09 43 17 27.4 0.95 + .06 3C 254 1 1 1 1 53 . 1 1 40 53 41.1 0.79 + .05 1127-145 1 1 27 35.69 -14 32 54.9 7.31 + . 1 5 1128+455 1 1 28 56. 38 45 31 24.9 0.65 + .01 3C 263 1 1 37 10.80 66 04 24.0 1 .04 + .04 1 138 + 015 1 1 38 34 . 40 01 30 57.5 0.93 + .03 3C 267 1 1 47 22. 1 0 1 3 04 00.0 0.59 + .07 1148-001 1 1 48 10.12 -00 07 13.1 1 .97 + .04 1153+317 1 1 53 44. 13 31 44 46.4 0.95 + .04 1201-041 1 2 01 28.52 -04 06 00.2 1 .00 + .03 3C 268.4 1 2 06 41 .98 43 55 59.9 0.60 + .03 3C 270.1 1 2 18 03.84 33 59 46.6 0.87 + . 04 1225+368 1 2 25 30.74 36 51 47.4 0.77 + .01 1237-101 1 2 37 07.29 -1 0 07 00.6 1 .53 + .05 3C 277 . 1 1 2 50 15.19 56 50 37.0 1 .05 + .04 3C 280 1 2 54 41 . 07 47 36 32.6 1 .53 + .06 1 306-095 1 3 06 02.03 -09 34 31.5 2.00 + .05 1318+113 1 3 1 8 49.67 1 1 22 29.0 0.77 + .03 3C 287 1 3 28 15.96 25 24 37.0 3.26 + .06 3C 288 1 3 36 38.36 39 06 22.3 0.99 + .06 1 345+125 1 3 45 06. 1 9 1 2 32 20.0 2.71 + .04 1 358 + 624 1 3 58 58.30 62 25 08.4 1 .77 + .02 3C 295 1 4 09 33.50 52 26 13.0 6.53 + .08 OQ 323 1 4 1 3 56.29 34 58 29.5 1 .35 + . 1 4 3C 299 1 4 19 06.41 41 58 30.0 0.90 + .05 1434+036 1 4 34 25.87 03 37 11.3 1 .28 + .02 38 Table I I I . Continued Source R.A h . (1950) m s DEC 0 (1950) Flux Density (Jansky) 3C 305 1 4 48 17.48 63 28 36.0 0.92 + .04 3C 309.1 1 4 58 56.61 71 52 11.3 3.76 + .06 1509+015 1 5 09 52.92 01 32 21 .7 0.68 + .05 3C 317 1 5 14 16.97 07 1 2 16.6 0.87 + .04 3C 318 1 5 17 50.67 20 26 54.2 0.75 + .03 3C 321 1 5 29 40.83 24 1 2 47.9 1 .22 + .04 3C 323.1 1 5 45 31 .30 21 01 38.5 0.92 + .07 1548+05 1 5 48 07.00 05 36 11.0 2.54 + .06 3C 326.1 1 5 53 57.30 20 1 3 00. 5 0.86 + .06 1 555 + 00 15 55 17.68 00 06 44.2 1 .71 + .05 1607+268 1 6 07 09.29 26 49 18.7 1 .58 + .06 DA 406 1 6 1 1 47.93 34 30 19.9 2.67 + .06 3C 334 1 6 18 06.81 1 7 43 37.7 0.57 + .03 3C 337 1 6 27 19.75 44 25 37.4 0.91 + .03 3C 345 1 6 41 17.61 39 54 10.9 5.65 + .08 3C 349 16 58 05.06 47 07 08.5 1.14 + .04 3C 353 17 09 17.94 46 05 06.3 21 .5 + .30 1716+006 1 7 16 49.86 00 40 11.3 0.77 .05 3C 362 1 7 44 56.20 1 8 23 17.0 - + 1756+134 17 56 13.35 1 3 28 43.9 0.66 + .03 1749+701 1 7 49 03.40 70 06 39.8 - + 3C 371 18 07 18.55 69 48 57. 1 1 .74 + .05 1819+396 18 19 42. 39 39 41 13.8 0.97 + .01 3C 380 18 28 13.41 48 42 40.5 7.50 + .09 1829+290 18 29 17.94 29 04 57.2 1.15 + .04 3C 388 18 42 35.49 45 30 22.4 1 . 77 + .04 3C 390 18 43 1 5. 29 09 50 31.0 1 .77 + .05 OV+080 19 47 39.20 07 59 16.0 0.80 + .05 DR 21 20 37 14.20 42 09 07.0 21 .0 + .50 NGC 7027 21 05 09.39 42 02 03. 1 5.44 + .05 39 2. Instrumental P r o f i l e s T h i s s e c t i o n begins by d e s c r i b i n g the measurements of the i n s t r u m e n t a l p r o f i l e s obtained i n August 1980. The 1980 r e s u l t s are then compared to the l e s s e x t e n s i v e c a l i b r a t i o n s c a r r i e d out d u r i n g the 1977 to 1979 observing s e s s i o n s . On the b a s i s of t h i s comparison the a p p l i c a t i o n of the 1980 r e s u l t s to the e a r l i e r years i s d i s c u s s e d . The North-South and East-West ' c r o s s - s e c t i o n s of the i n s t r u m e n t a l p r o f i l e were measured by scanning through the beams with a c a l i b r a t i o n source. Three types of scans were employed: 1) 90° d r i f t scans - the feed box i s r o t a t e d to 90° and as the e a r t h r o t a t e s the source " d r i f t s " through the center of both beams. 2) 0° d r i f t scans - the feed box i s at 0° and the source d r i f t s through e i t h e r beam A or beam B. 3) Driven scans — the t e l e s c o p e i s d r i v e n along the meridian at a rate of 60 '/min, with the feed box r o t a t e d so that the beams are a l i g n e d along the scan t r a c k , and the source passes through the center of each beam. Driven scans are c a r r i e d out i n both the northbound and southbound d i r e c t i o n . For d r i f t scans the i n t e g r a t i o n time i s i n c r e a s e d to 1.0 seconds. The sample rate of 1 Hz adequately d e f i n e s the beam p r o f i l e , y i e l d i n g , f o r a 3' beam, a minimum samples per beam width of 12, at the c e l e s t i a l equator, and 24 at 6=60°. The 40 runs r e c e i v e r noise f o r the average of both r e c e i v e r s i s 6 mK. Driven scans are sampled at the survey rate of 5 Hz, p r o v i d i n g about 15 samples per HPBW and an rms r e c e i v e r noise of 11 mK. The t y p i c a l f l u x d e n s i t y of a c a l i b r a t i o n source i s about one Jansky, and the t e l e s c o p e s e n s i t i v i t y ranges from about 0.5 to 1.0 K/Jy. The r e f o r e , with a r e c e i v e r noise of about 10 mK, measurements of the beam p r o f i l e s , with good s i g n a l to noise r a t i o , can be obtained, i n most cases, to a l e v e l of about 5% of the p r o f i l e peak. The high s i g n a l to noise of the d r i f t scans p r o v i d e s an o p p o r t u n i t y to check the beam p r o f i l e s f o r s i d e — l o b e s t r u c t u r e . F i g u r e 6 shows the 0° r e s u l t s for both beams from d r i f t scans through the strong source 3C 295 (S=6.5 J y ) . A s i n g l e s i d e — l o b e , s i t u a t e d 5 arc—minutes west of the beam, i s evident i n scans through both beams. The magnitude of the s i d e — l o b e i s about -15 db of the beam peak. Driven scans show no s i d e — l o b e s , down to a l e v e l of -30 db, w i t h i n one degree of the beams i n the north—south d i r e c t i o n . The beam p r o f i l e measurements are obtained by f i r s t c a r r y i n g out the 90° d r i f t s scans to measure the r i g h t a s c e n s i o n p o i n t i n g c o r r e c t i o n s . These c o r r e c t i o n s are a p p l i e d to the s t a r t c o - o r d i n a t e s of the d r i v e n scans to center the scan at the observed r i g h t a scension of the c a l i b r a t i o n source. From the d e c l i n a t i o n p o i n t i n g c o r r e c t i o n s given by the d r i v e n scans and the beam s e p a r a t i o n from the 90° d r i f t scans, the d e c l i n a t i o n of the 0° d r i f t scans which w i l l p l a c e each beam center in turn at the observed d e c l i n a t i o n of the c a l i b r a t i o n 41 Beam A Beam B w Figure 6. - 1 0 - 5 0 (ARC-MIN) 1 0 D r i f t scans at 0 ro tat ion angle through 3C 295. The side-s ituated 5 arc-minutes west of the beams i s -15db r e l a t i ve beam peaks. lobe, to the 42 source i s c a l c u l a t e d . Since the sources used as c a l i b r a t o r s d i f f e r between observing s e s s i o n s , a d i r e c t comparision of the measured p r o f i l e s i s not p o s s i b l e . For t h i s reason, and to f a c i l i t a t e computer s i m u l a t i o n of the beam shapes f o r data r e d u c t i o n , a mathematical model of the beams was c o n s t r u c t e d ; with the d e c l i n a t i o n dependence of the p r o f i l e s c o n t a i n e d i n the model parameters. The model adopted i s a m o d i f i c a t i o n of a simple, f i r s t order gaussian beam approximation. The unmodified gaussian component has the same HPBW as the measured p r o f i l e . A c o r r e c t i o n f u n c t i o n i n the ex p o n e n t i a l p o r t i o n of the gaussian i s used to match the model to the measurements. The model i s expressed i n equation I I I . 1 , P(x,c)=exp{-2.7726[1+C X ( X-1/2)]x 2} , (111 . 1 ) where the v a r i a b l e x i s the angular o f f s e t from the p r o f i l e peak measured i n half-power beam widths. It i s obvious from the equation that the model i s equal to a simple gaussian, with the same HPBW, at x=0 and X=1/2, Since the unmodified gaussian and the p r o f i l e have the same HPBW, the model matches the p r o f i l e at these p o i n t s . The q u a d r a t i c c o r r e c t i o n f u n c t i o n was found to produce good agreement with the measured p r o f i l e s , and has the a d d i t i o n a l advantage of having only one f r e e parameter when c o n s t r a i n e d to a value of one at 0 and 1/2. The model i s t h e r e f o r e completely s p e c i f i e d by two parameters; the HPBW of the p r o f i l e and the c o e f f i c i e n t "c" in the c o r r e c t i o n f u n c t i o n . To accommodate beam assymetry each s i d e of the beam p r o f i l e i s modelled independently. A f t e r removing a l i n e a r 43 b a s e l i n e from each c a l i b r a t i o n scan, the scan p o s i t i o n and amplitude ( p m , T m ) of the maximum of each beam response, and the width at h a l f maximum of both s i d e s of the p r o f i l e s , are measured. The model i s then f i t to the data set (x. ,y; ); where X j , as in equation I I I . 1 , i s the d i s t a n c e i n h a l f - w i d t h s of each data sample from p m and y-, i s the sample antenna temperature measured r e l a t i v e to the maximum (T-, /T m) . The f i t extends to the f i r s t data sample with amplitude below 10% of the peak, which, in p r a c t i c e , i s 6-7% and corresponds to a value of X j of about 1. The c o e f f i c i e n t c i s determined by a l e a s t squares method that minimizes the d i f f e r e n c e between the p r o f i l e and the model. In f i g u r e 7, measured p r o f i l e s are compared to both a simple gaussian and the complete beam model, for two c a l i b r a t i o n sources at g r e a t l y d i f f e r e n t d e c l i n a t i o n s . The agreement between the model and the p r o f i l e i s q u i t e good (<2%) over the e n t i r e range of the f i t . The r e s u l t s of the model f i t s to the 1980 0° d r i f t scans (East-West p r o f i l e ) and d r i v e n scans (North-South p r o f i l e ) data are shown i n f i g u r e s 8 and 9. The s o l i d curves are f o u r t h order polynomial f i t s to the d e c l i n a t i o n dependence of the model parameters. T y p i c a l rms s c a t t e r about the polynomial f i t s i s 0.05 arc-min f o r the HPBW and 0.1 f o r c. At d e c l i n a t i o n s l e s s than about -10°, severe beam d i s t o r t i o n occurs and the model i s no longer a p p l i c a b l e . The d e c l i n a t i o n dependence of the se p a r a t i o n of the beams, d e r i v e d from both the 90° d r i f t scans and the d r i v e n scans, i s shown in f i g u r e 10. No apparent d i f f e r e n c e e x i s t s between the 44 Figure 7. Comparison of the beam model to measured p r o f i l e s . The beam pro f i l e s (data points) are compared to a simple gaussian ( l e f t ) and the complete beam model ( r i gh t ) . 45 A (East) - . * t * ..it . * n . A (West) HPBW • * »"»• • • • • V— HPBW /L * *"* " * ' * : c i i 1 i 1 i i • • >>-• • C B(East) ~*"TT t * W . | — « . - _ - % B (West) HPBW S ™ \H—n V — V t » » — r * — HPBW • c 1 1 I ' - 1 L -1 1 • *. •. • • * # • C • i i i i i i — _ i _ 1 0 2 0 3 0 4 0 5 0 6 0 7 0 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 Declination (°) Figure 8. East-West beam model parameters in 1980. 46 A(North) • • v ^ 1 * » * — * HPBW A(South) HPBW • • c c B(North) • • •• •• • HPBW B(South) , • » • » • — • • HPBW • • >^ • • -.• S c 1 1 1 1 1 J 1 L _ • • • ^ — • • • • C i 1 I 1 1 1 1 L _ 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 Declination (°) Figure 9. North-South beam model parameters in 1980. 8 7 1 1 1 1 - r i i i . . . . 1 — o • 0 - 0 -o o 0 o - o -- -• -V 0 0 o o -v..° o V o • • o ° o 0 o o ° <» o» - o o o «. • • •« oo • o § o • o -0 0 -1 1 1 1 1 1 1 -10 0 10 20 30 40 50 60 70 Declination (°) Figure 10. 1980 beam separations, at feed box rotat ion angle of 0 (open c i r c l e s ) and of 90 (dots). 48 results from the two types of scans. The beam separations are therefore taken to be independent of the rotation angle of the feed box. Before applying the 1980 results to the 1977 to 79 ca l i b r a t i o n s , the p o s s i b i l i t y of a change in the beam shapes between observing sessions must be considered. With the exception of 1978, when a diff e r e n t focus setting was used, the physical parameters of the antenna and feed system were id e n t i c a l for a l l observing sessions. Consequently, the beam shapes should remain unchanged. As a check, the beam model parameters from f i t s to the 90° d r i f t scan p r o f i l e s in 1977, 1979 and 1980 were compared. This comparison is shown in figure 11. Because the t a i l of the inner p r o f i l e in these scans may be affected by the proximity of the beams, to. simplify the comparison, only the outer p r o f i l e of each beam (A West and B East) i s used. It is obvious from the figures that, within the error on the model parameters, the 1977, 1979 and 1980 beam p r o f i l e s are i d e n t i c a l . The 1980 beam models may therefore be applied d i r e c t l y to the 1977 and 1979 observat ions. In 1978, however, the di f f e r e n t focus setting produced a s i g n i f i c a n t change in the shape of the beams. Thus, in this case, some intermediate steps are required to obtain the appropriate 0° p r o f i l e s . The magnitude of the difference, in both the shape of the beams and the peak beam gains, between 1978 and the other observing sessions is a maximum of about 20%. This effect is small enough that, as a reasonable f i r s t i i i i • i 1 1 r— • 5 - A ( W e s t ) O O *> • 0 o 0 H P B W > i i i i i •••• i r ~ B ( E a s t ) o A o H P B W C — 1 _ i i I I I . i c 1— 1 1 1 I 1 ' 1 0 10 20 30 40 5 0 60 70 0 10 20 30 40 50 60 70 Declination (°) re 11. Beam model parameters at 90° rotat ion angle. Model parameters for beam A west and B east are shown for 1980 (dots), 1979 (open c i r c l e s ) and 1977 ( t r iang les ) . 50 approx imat ion , one might assume that the change i n the focus s e t t i n g in 1978 e f f e c t s each beam p r o f i l e i n a s i m i l a r f a s h i o n . In t h i s case , a s i n g l e , d e c l i n a t i o n dependent t r ans fo rmat ion i s s u f f i c i e n t to map each 1980 beam p r o f i l e i n t o the corresponding 1978 p r o f i l e . Th i s i s e q u i v a l e n t to the statement that the r e l a t i o n s h i p between d i f f e r e n t p o r t i o n s of the beams d u r i n g any one year does not change. That i s , for example, i f both the nor th and south p r o f i l e s of the beams t rans form from 1980 to 1978 i n an i d e n t i c a l f a s h i o n , then the r e l a t i o n s h i p between the nor th and south beam p r o f i l e s w i l l be i d e n t i c a l i n both 1978 and 1980. There fore , a comparison of the r e l a t i o n s h i p between two beam p r o f i l e s in each year prov ides a t e s t of the i n i t i a l assumption. In f i g u r e 12, the r e l a t i o n s h i p between the North and South p r o f i l e s of the beams i s shown by a comparison of the beam model parameters obta ined from the d r i v e n scans. The data p o i n t s are the r e s u l t s from 1978, and the smooth curve i s the po lynomia l f i t to the 1980 r e s u l t s . The r e l a t i o n s h i p between the p r o f i l e s i s i d e n t i c a l for the two observ ing s e s s ions ; imply ing that the t r ans fo rmat ion from 1980 to 1978 beam p r o f i l e s i s independent of the p a r t i c u l a r p r o f i l e c o n s i d e r e d . The d e c l i n a t i o n dependent convers ion f a c t o r s , for c o n v e r t i n g 1980 beam model parameters to 1978, are shown in f i g u r e 13. The f a c t o r s were c a l c u l a t e d us ing the po lynomia l f i t s to the North-South p r o f i l e s of each beam i n both observ ing s e s s ions . Each of the four p r o f i l e s prov ides an independent measure of the convers ion f a c t o r . The e r r o r bars represent the one sigma s c a t t e r in the four va lues for each p o i n t . • • I I I I I I I I I 1 1 1 1 1 L_ 0 10 20 30 40 50 60 70 0 10 20 30 40 50 60 70 Declination (°) Figure 12. The relat ionship between model parameters for the north and south portions of the beams. The smooth curves are from the polynomial f i t s to the 1980 beams, and the data points are measurements from indiv idual sources in 1978. 52 Declination ( ° ) Figure 13. The 1980 to 1978 beam model conversion factors. I I I I I E -2 -I 0 I 2 W (arc-minutes) Figure 14. Comparison of the 1978 beam models (curves) to the driven scan results (data points ) . 54 In 1978, f o r a small number of c a l i b r a t i o n sources, a set of f i v e p a r a l l e l d r i v e n scans, separated by 1', were executed about the source p o s i t i o n . These scans were c a r r i e d out to o b t a i n accurate p o i n t i n g i n f o r m a t i o n . However, the amplitude of the s i g n a l i n each scan, as a f u n c t i o n of the d i s t a n c e of the scan from the observed source p o s i t i o n , p r o v i d e s a f i n a l check on the c o n v e r s i o n of the 1980 to 1978 beam p r o f i l s . In f i g u r e 14, these r e s u l t s are p l o t t e d along with the computed beam model f o r three r e p r e s e n t a t i v e sources. In a l l cases, the d e v i a t i o n s between the two r e s u l t s are c o n s i s t e n t with the e r r o r s . 3.0 P o i n t i n g and Gain The c o - o r d i n a t e s of the t e l e s c o p e are d e f i n e d by the p o s i t i o n of the p r o j e c t i o n of the center of the prime focus feed box onto the c e l e s t i a l sphere. Comparison of the beam p o s i t i o n s at r o t a t i o n angles of 90° and 270° shows that the d i f f e r e n c e between t h i s p o i n t and the center of r o t a t i o n of the beams i s no g r e a t e r than 7". Since t h i s d i f f e r e n c e i s l e s s than the accuracy of source p o s i t i o n measurements, the center of the feed box and the center of r o t a t i o n of the beams are taken to be c o - i n c i d e n t . The observed c o - o r d i n a t e s of a source t h e r e f o r e correspond to the p o i n t midway between the peaks produced by each beam from a scan through the source. P o i n t i n g c o r r e c t i o n s and beam gains are determined by comparing the observed c o - o r d i n a t e s and s t r e n g t h s to the known c o - o r d i n a t e s and f l u x d e n s i t i e s of the c a l i b r a t i o n sources. 55 Because the approach taken to determine the pointing and gain c a l i b r a t i o n s d i f f e r from year to year, the method and results are discussed separately for each observing session. 3.1 1979 The 1979 pointing errors were obtained by carrying out two d r i f t scans through each c a l i b r a t i o n source; one at 90° rotation angle and another, at the same declination, with a rotation angle of 7 9 ° . The 79° scan produces a beam orientation with respect to the scan track that i s i d e n t i c a l to a survey type scan. The offset of the source from the scan declination is given, in the same manner, by the ra t i o of the beam responses. The observed right ascension of the source is given by the mean position of the beam peaks in the 90° scan, and the observed declination i s given by the scan declination plus the offset ( e ) . For the purpose of cal c u l a t i n g e, the beams are taken to be gaussian with HPBW (4>) equal to the measured HPBW of the 90° p r o f i l e s . Since the maximum measured value of e, about 2 0 " , is a small fraction of a beam width, the error introduced by adopting t h i s approximation is ne g l i g i b l e . In t h i s case the offset is given by equation I I I . 2 , 0=.95(Ab) - 1 Un[B(90)/B(79) ] * b 2-In [ A ( 90 )/A ( 79 ) ] $Q2 } (III .2) where Ab is the beam separation, and the argument of the logarithms is the ra t i o of the peak amplitude of the beam responses at 90° and 79° rotation angle. Declination pointing errors were obtained for a further fiv e sources by carrying out a set of driven scans about the 56 source position. Each set consists of a maximum of 5 p a r a l l e l driven scans separated by 1 arc-min. The central scan i s driven through the catalogued co-ordinates of the source. The observed source position i s obtained by interpolation, using the beam amplitudes in the three scans that bracket the source. The right ascension and declination pointing corrections are shown in figure 15; Declination corrections derived from the driven scans are shown as open c i r l e s . The rms scatter about the polynomial f i t s to the declination dependence i s 8" for Ao and 19" for A6. For data reduction purposes, the gains of the beams are expressed as the absolute gain of beam A (G a), and the r a t i o of the gain of beam A to beam B (R 0). In the o r i g i n a l c a l i b r a t i o n scheme (see section III.1), the gains of the beams were assumed to be independent of rotation angle, and G a and R0 were calculated from the beam amplitudes, K Q and Kb, in the 90° d r i f t scans. However, in 1980, examination of the gains obtained from the 90° and 0° d r i f t scans showed this assumption to be erroneous. Figure 16 shows a comparision of the 0° and 90° gains, based on the 1980 r e s u l t s . From the figure i t is evident that, between rotation angles 0° and 90°, the gains change by up to 20%-30%. The equivalence of the beam shapes in 1979 and 1980 indicates that the curves in figure 16 can be used to convert the 1979 90° gains to the correct 0° values. To check t h i s , 1979 0° gains were calculated using fiv e sources through which sets of driven scans were carr i e d out. Peak beam antenna 4h 2h 10-0 --10--20 -30--40 -i 1 1 r • •• J L J I I I L • • • J 1 1 1 I i i ' 0 10 20 30 U0 50 Declination (°) 60 70 Figure 15. The 1979 telescope pointing corrections, 58 Dec I i no t i on ( 0 ) Figure 16. Conversion factors from gain at 90 rotat ion angle to gain at 0 rotat ion angle. Dots are 1980 results and open c i r c l e s are 1979 resu l t s . 60 temperatures are calculated by gaussian interpolation of the beam amplitudes in the three scans closest to the observed source position. The 90° to 0° conversion factors, based on comparing these driven scan results to the gains obtained from the 90° d r i f t scans, are plotted as open c i r c l e s in figure 16. The agreement, between these data and the 1980 results confirm the v a l i d i t y of using the 1980 conversion factors for the 1979 observing session. The 1979 0° gains obtained from the 90° d r i f t scans, by carrying out thi s conversion, are shown in figure 17. The rms scatter about the polynimial f i t i s 7.6%. 3.2 1978 The 1978 pointing errors were determined solely via driven scans. Observed co-ordinates were calculated by interpolating the data from three scans bracketing the source postion. The resulting pointing corrections are shown in figure 18. The d i s s i m i l a r i t y of the beam shapes between 1978 and 1980, caution that the 1980 90° to 0° gain conversions are not applicable in this year. Therefore, 0° gains were also calculated from the sets of driven scans. Peak beam antenna temperatures were obtained, as in 1979, by gaussian interpolation of the beam peaks in the three scans closest to the observed source position. Since the farthest scan is less that 1.5 arc-min from the source position, the error introduced by the non-gaussian nature of the beams is <1% (see figure 7). This error is negligible compared to the primary source of error; the uncertainty in the observed source position, that 61 4 • / (sec) 3 a < 2 - • • 1 1 1 1 • i i 60 AO -20 • -00 < 0 • — • --20 • • --40 1 1 1 i i i 0 10 20 30 40 50 60 70 Declination (°) Figure 18. The 1978 telescope pointing corrections. Figure 19. The 1978 0° beam gains. 63 introduces an uncertainty in the peak antenna temperature of up to 10%. The derived gains are plotted in figure 19. The increased uncertainty in these data, compared to the 1979 r e s u l t s , is reflected in the increase to 9.8% in the scatter about the f i t to the declination dependence. 3.3 1977 Because of the loss of the c a l i b r a t i o n data in 1977, the pointing and gain c a l i b r a t i o n s were carr i e d out using a sample of strong survey sources. The source strengths and co-ordinates were calibrated against the 1979 values for the same source. The 1979 observing session was chosen as a standard for two reasons; 1) the 1979 c a l i b r a t i o n s are the most accurate, and 2) comparison of the beam p r o f i l e s (figure 11) indicate that the 1977 and 1979 beam properties are si m i l a r . A strength and position for each source in 1977 were calculated using the 1979 beam p r o f i l e s (equivalent to 1980) and 0° gain r a t i o . From the sources detected in both 1977 and 1979, a subset of 29 stong sources with constant flux density was extracted. The method used to determine which sources are flux stable is described in d e t a i l in section V.2. Based on t h i s sample of sources, the r a t i o of source strengths, and the difference in telescope pointing between 1977 and 1979 were measured. The results are shown in figures 20 and 21. Application of these correction factors to the 1977 survey results provides a data base with the same absolute gain and pointing errors as the 1979 data base. Fi n a l flux densities 0 10 20 30 40 50 Decl inat ion (°) Figure 20. The r a t i o of 1979 to 1977 source strengths, 65 5 u CD CO 0) I*-^ 0 a - 5 Z 20 0 0> £ -20 ^ - 4 0 -60 -- • - • • • - • — • — - • • -• 1 1 1 1 | 1 1 1 • • • _ — • • — • • • • • - • -1 1 1 1 1 1 1 1 10 20 30 40 50 60 70 Declination (°) Figure 21. The difference in the telescope pointing corrections between 1977 and 1979. 66 and source positions are obtained by further applying the 1979 gain and pointing corrections. 4. Uncertainties While errors in the c a l i b r a t i o n measurements described in this chapter do not effect the measurement of short—term v a r i a b i l i t y , the accuracy of the mean flux density and position calculated for the survey sources depends both on the v a l i d i t y of the beam model, and, on the errors in the model parameters and the gain and pointing c a l i b r a t i o n s . In th i s section, the magnitude of these uncertainties, and the l i m i t s on possible systematic errors in the c a l i b r a t i o n s are discussed. Deviations between the beam model and the true beam p r o f i l e w i l l produce systematic errors that may be a function of the offset of a source from the central scan track. The v a l i d i t y of the beam model was checked by measuring the difference between the model and the measured p r o f i l e s as a function of the variable x (the distance from the beam peak in units of the HPBW). Figure 22 shows, for the East—West beam p r o f i l e s in 1980, the mean difference expressed as a percentage of the actual p r o f i l e ; averaged over a l l sources used to determine the model parameters. The error bars represent' the one sigma scatter in the difference between the model and p r o f i l e for a l l sources. Over the entire range 0<x<1, the mean deviation from the actual p r o f i l e i s < 1%. The scatter about the mean, which reaches a le v e l of ~-l0% at x=1, can be accounted for by the effects of noise on the measured p r o f i l e s . 67 0) u e a> c o .2 .4 .6 Distance from peak (HPBW's) Figure 22. Errors on the model as a function of X. The quantity plotted i s the mean difference between the model and the actual East-West source p ro f i l e s for the ca l ib ra t ion sources used to measure the model parameters. The error bars are the one sigma scatter on the d i f ference. 68 The magnitude of the scatter agrees well with the calculated uncertainties based on the errors in the beam model parameters; given by the rms scatter of the measurements about the smooth f i t to their declination dependence, about 0.05 arc-min for the HPBW and 0.1 for c. Systematic errors in the calculated source strengths and of f s e t s , a r i s i n g from the errors in the model parameters, are a maximum at large offsets of about 3% and 0.1 arc-min respectively. In 1978, the uncertainties in the conversion factors (figure 13) introduce additional, and possibly systematic, uncertainties of comparable magnitude. However, these errors are, in general, much smaller than the effe c t s of noise on the estimates of the signal strength, for a t y p i c a l survey source, and the errors on the absolute gain and pointing c a l i b r a t i o n s . An estimate of the errors in a single measurement of the beam gains i s provided by the rms scatter of the measured values about the smooth curve f i t to their declination dependence. This scatter is a result of both the random error due to noise in the measurement of signal strengths, and the errors on the absolute flux densities of the c a l i b r a t i o n sources. In 1978 and 1979 the one sigma scatter about the smooth f i t i s 9.8% and 7.6%, respectively. Because of the averaging nature of the curve f i t t i n g procedure, the error on the curve values is smaller than the one sigma scatter. T y p i c a l l y , the errors on the curve values are about 5%. However, i t should be noted that the curves are better defined at some declinations than at others. In p a r t i c u l a r , at low 69 d e c l i n a t i o n s (6<0°) e r r o r s as l a r g e as 10%—20% cannot be r u l e d out. In 1977 the a d d i t i o n a l e r r o r i n troduced by c o n v e r s i o n to 1979 source s t r e n g t h s i n c r e a s e s the t y p i c a l e r r o r on the f i n a l gain to about 10%. From s i m i l a r c o n s i d e r a t i o n s , one sigma e r r o r s i n the p o i n t i n g c o r r e c t i o n s are about 10 " f o r r i g h t ascension and 20" for d e c l i n a t i o n in 1978 and 1979; and approximately 15" and 30" f o r 1977. Although the c a l i b r a t i o n measurements y i e l d c o n s i s t e n t r e s u l t s to w i t h i n the quoted e r r o r s ; because the c a l i b r a t i o n data are a c q u i r e d in a d i f f e r e n t manner from the survey data base, the p o s s i b i l i t y e x i s t s t h at systematic e r r o r s may a r i s e when the gain and p o i n t i n g c a l i b r a t i o n s are a p p l i e d to the survey r e s u l t s . To check f o r any such e f f e c t s , a number of c a l i b r a t i o n sources are i n c l u d e d i n each days survey o b s e r v a t i o n s . These sources are observed with survey type scans and the data are processed i n a manner i d e n t i c a l to the survey data. Table IV l i s t s f o r each year the rms d i f f e r e n c e between the observed and catalogued f l u x d e n s i t y and p o s i t i o n fo r these sources, a f t e r a p p l i c a t i o n of the gain and p o i n t i n g c a l i b r a t i o n s . The r e s u l t s are c o n s i s t e n t with the e r r o r s on the c a l i b r a t i o n measurements, i n d i c a t i n g that the magnitude of any systematic e f f e c t s i s no g r e a t e r than the u n c e r t a i n t i e s i n the c a l i b r a t i o n s . As a f u r t h e r check on the accuracy of survey c o - o r d i n a t e s , independent p o s i t i o n s were measured for a sample of strong sources d e t e c t e d in the survey r e g i o n , using the Algonquin 70 Radio Observatory 46 meter t e l e s c o p e . The ob s e r v a t i o n s were c a r r i e d out at 10.5 GHz. Thus the beam s i z e i s approximately the same as f o r the survey o b s e r v a t i o n s . Accurate p o s i t i o n s were obtained by executing a number of repeated back and f o r t h scans, through the observed source p o s i t i o n , i n both the r i g h t a scension and d e c l i n a t i o n d i r e c t i o n . By c a r e f u l c a l i b r a t i o n of the t e l e s c o p e p o i n t i n g e r r o r before and a f t e r each o b s e r v a t i o n , p o s i t i o n s f o r sources stronger than about 200 mJy can be measured to about 5 arc seconds. Ten of the sources observed had 10.5 GHz f l u x d e n s i t y l a r g e enough fo provide good p o s i t i o n s . In f i g u r e 23 the d i f f e r e n c e between the ARO and survey c o - o r d i n a t e s f o r these ten sources, and the d i f f e r e n c e between the catalogued and survey c o - o r d i n a t e s f o r the c a l i b r a t i o n sources i n c l u d e d i n the survey o b s e r v a t i o n s , are p l o t t e d as a f u n c t i o n of d e c l i n a t i o n . No s i g n i f i c a n t systematic e f f e c t i s ev i d e n t . The peak to peak s c a t t e r i n the data i s c o n s i s t e n t with the estimated one sigma e r r o r of 10" for r i g h t ascension and 20" f o r d e c l i n a t i o n . 71 Table IV. E r r o r s on P o s i t i o n and Flux D e n s i t y C a l i b r a t i o n s No. One sigma s c a t t e r i n the d i f f e r e n c e between DATE of Catalogued and Survey Values. Obs. Ac(") A6 ( " ) AS(%) 1977 3 5 9 10.8 1 978 8 9 1 7 7.3 1979 8 8 20 5.7 72 20 30 40 50 Declination (°) Figure 23. Errors on the survey co-ordinates. The dots are the difference between survey co-ordinates and co-ordinates measured at ARO for a sample of strong survey sources. Open c i r c l e s represent the difference between survey and catalogued co-ordinates for the ca l ib ra t ion sources included in the survey observations. 73 CHAPTER IV SEARCH FOR COMPACT SOURCES 1 . I n t r o d u c t i o n From n o n — r e l a t i v i s t i c c a u s a l i t y arguments, v a r i a b i l i t y on a time s c a l e r o r i g i n a t e s from an emission region with dimension < c r . Thus, an emission region e x h i b i t i n g d a i l y f l u x v a r i a t i o n s would be unresolved by a 3 arc-minute beam at d i s t a n c e s g r e a t e r than about one parsec. Since t h i s d i s t a n c e i s comparable to that to the nearest s t a r , i t seems j u s t i f i a b l e to c o n f i n e the search f o r d a i l y v a r i a b i l i t y to unresolved sources. For the longest measured time s c a l e of about one year, t h i s l i m i t i s 300 p a r s e c s , t h e r e f o r e , the case f o r unresolved sources i s l e s s s t r a i g h t f o r w a r d . However, to expect one such source w i t h i n 300 pc would r e q u i r e a space d e n s i t y s i m i l a r to the d e n s i t y of a l l g a l a c t i c r a d i o sources. To the degree that t h i s i s u n l i k e l y , one can c o n f i d e n t l y r e s t r i c t the search for v a r i a b i l i t y to unresolved sources of emission. The recent evidence f o r the r o l e of bulk r e l a t i v i s t i c motions in some of the known, e x t r a g a l a c t i c v a r i a b l e r a d i o sources (see chapter I) does l i t t l e to weaken t h i s argument. An a d d i t i o n a l motive f o r searching the survey data f o r compact sources i s the unique s e n s i t i v i t y of t h i s survey compared to other surveys of the plane. P r e v i o u s l y , the most s e n s i t i v e survey of a l a r g e p o r t i o n of the g a l a c t i c plane was c a r r i e d out with the Bonn 100 meter t e l e s c o p e ( A l t e n h o f f et a l . 1980), and covered the g a l a c t i c l o n g i t u d e i n t e r v a l 358°<1<60°. 74 While t h i s t e l e s c o p e has comparable s e n s i t i v i t y and r e s o l u t i o n to the NRAO 91 meter t e l e s o p e , the o b s e r v a t i o n s were c a r r i e d out i n the t o t a l power mode. Thus, in the presence of strong emission from g a l a c t i c s t r u c t u r e , the minimum detectabLe f l u x d e n s i t y was l i m i t e d by dynamic range to about 200 mJy. The present survey, on the other hand, i s i d e a l l y s u i t e d , because of the beam—switching technique, to the d e t e c t i o n of compact sources, and, by averaging many repeats of a scan through a given p o r t i o n of the plane, compact sources can be d e t e c t e d to l e v e l s of about 20 mJy; an improvement of a f a c t o r of ten. Furthermore, the o v e r l a p of the Bonn survey with the present survey i s only 20° of l o n g i t u d e . For the m a j o r i t y of the survey region (160° of l o n g i t u d e ) there has been no s e n s i t i v e survey at cm wavelengths. T h e r e f o r e , in a d d i t i o n to measuring v a r i a b i l i t y , t h i s survey p r o v i d e s a l i s t of newly d e t e c t e d compact r a d i o sources in the g a l a c t i c plane. T h i s chapter d e s c r i b e s the method used to search f o r compact sources in the data, and the t e s t s c a r r i e d out to determine the e f f i c i e n c y and accuracy of the search. 2. E d i t i n g Because of the l a r g e q u a n t i t y of data r e s u l t i n g from the survey o b s e r v a t i o n s , i t i s impossible to examine each scan i n f i n e d e t a i l . T h e r e f o r e , e d i t i n g based on a d e t a i l e d comparison of the data to "expected" r e s u l t s must be c a r r i e d out by computer, and, s i n c e the very phenomena being searched f o r i s , in a manner of speaking, an anomaly in the data, unless the 75 computer a l g o r i t h m i s very d i s c e r n i n g , the r i s k i s run of over e d i t i n g the data and i n t r o d u c i n g s e l e c t i o n e f f e c t s . T h e r e f o r e , p r i o r to the a n a l y s i s , e d i t i n g based on a d e t a i l e d examination of the data i s not c a r r i e d out. I n i t i a l e d i t i n g i s c a r r i e d out based on the scan p r o p e r t i e s l i s t e d i n the header i n f o r m a t i o n f o r each scan. The observed s t a r t c o - o r d i n a t e s and d r i v i n g r a t e are compared to the commanded v a l u e s . Scans f o r which these values d i f f e r s i g n i f i c a n t l y were d e l e t e d . F u r t h e r e d i t i n g was c a r r i e d out by examining the s t r i p c h a r t recorder output. Scans that e x h i b i t l a r g e l y d i s c r e p a n t s i g n a l s , such as might be produced by malf u n c t i o n of the r e c e i v e r s or h i g h l y unstable atmospheric c o n d i t i o n s , are noted and e d i t e d . However, the s c a l e of the ch a r t r e c o r d i n g s i s i n s u f f i c i e n t to show more s u b t l e e f f e c t s . F i n a l e d i t i n g i s c a r r i e d out based on l i n e a r b a s e l i n e f i t s to each scan. The b a s e l i n e , which i s f i t to the e n t i r e scan, i s c a l c u l a t e d i n such a manner that the c o — e f f i c i e n t s of the f i t are independent, and provide a measure of the data mean and mean slope of the scan. The mean slope i s p r i m a r i l y a r e s u l t of the change i n s p i l l — o v e r r a d i a t i o n with d e c l i n a t i o n , and i s h i g h l y r e p r o d u c i b l e i n the same scan executed on d i f f e r e n t days of the same observing s e s s i o n . The presence of a v a r i a b l e source does not g r e a t l y e f f e c t the mean slope because of the S shaped instrumental p r o f i l e . Scans with a h i g h l y d i s c r e p a n t mean slope are e d i t e d from the data base. Any remaining bad data i s passed to the r e s t of the a n a l y s i s . However, t h i s a n a l y s i s , which i n c l u d e s a search f o r 76 v a r i a t i o n s , i s , i n e f f e c t , a very s o p h i s t i c a t e d e d i t i n g program which f l a g s anomalous data. A f t e r the a n a l y s i s , each case of p o s s i b l e v a r i a b i l i t y i s i n v e s t i g a t e d i n d i v i d u a l l y to ensure the q u a l i t y of the data. 3. The search 3.1 Method The search f o r compact sources i s c a r r i e d out by searching each scan f o r a s i g n a l that matches the p r o f i l e of an unresolved source. In order to maximize s i g n a l to noise the search i s c a r r i e d out on an average scan c o n s t r u c t e d by combining a l l the repeats of the same scan d u r i n g one observing s e s s i o n . In g e n e r a l , the optimum method f o r the d e t e c t i o n of a' s i g n a l i n the presence of noise i s to c r o s s - c o r r e l a t e the data with the instrumental p o i n t spread f u n c t i o n . However, in the survey data base, there are two e f f e c t s which complicate t h i s simple approach. F i r s t , the i n s t r u m e n t a l p r o f i l e i s not a f i x e d q u a n t i t y . Without p r i o r knowledge of the o f f s e t of a source from the scan t r a c k , the shape of the s i g n a l cannot be p r e d i c t e d . Second, the p r o f i l e may be superimposed on a l o c a l b a s e l i n e a r i s i n g from c u r v a t u r e i n the background r a d i a t i o n of extended emission in the g a l a c t i c plane. For a symmetric in s t r u m e n t a l p r o f i l e , s u i t a b l e manipulation of the data during c r o s s - c o r r e l a t i o n can remove the e f f e c t s of l i n e a r b a s e l i n e s . However, in the case of an asymmetric p r o f i l e , which i s the general case f o r a survey d e t e c t i o n , c r o s s - c o r r e l a t i o n of a 77 l i n e a r b a s e l i n e i n t r o d u c e s a d d i t i o n a l curvature which d i s t o r t s the r e s u l t . At the expense of some s i g n a l to noise r a t i o , these problems are overcome i f , i n s t e a d of a search f o r the complete in s t r u m e n t a l p r o f i l e , a search i s c a r r i e d out f o r each peak of the p r o f i l e independently. The r e s u l t s of the two searches are l a t e r combined, to t e s t f o r peak combinations that are c o n s i s t e n t with the f u l l i n s t r u m e n t a l p r o f i l e . The s i g n a l to noise r a t i o f o r a s i n g l e peak i s optimized by c r o s s - c o r r e l a t i n g the data with a gaussian that has a HPBW of 3 arc-min; approximately equal to the HPBW of the ins t r u m e n t a l p r o f i l e . The e q u i v a l e n t i n t e g r a t i o n time of 1.47 seconds reduces the r e c e i v e r noise power by a f a c t o r of about 3.4. However, the smoothing of the data r e s u l t s i n an a t t e n u a t i o n of the s i g n a l peak of about 30%. Thus, the net increase of the s i g n a l to noise r a t i o i s about a f a c t o r of 2.4. The remainder of the data r e d u c t i o n i s c a r r i e d out on the smoothed data s e t . In a d d i t i o n to the problem of changes i n t h e . b a s e l i n e l e v e l i n regions of h i g h l y s t r u c t u r e d extended emission, a slow d r i f t i n the d i f f e r e n t i a l output of the r e c e i v e r s occurs across a scan, as a r e s u l t of the v a r i a t i o n in the pickup of ground s p i l l - o v e r r a d i a t i o n with d e c l i n a t i o n . T h i s e f f e c t i s w e l l represented by a l i n e a r b a s e l i n e over the len g t h of the scan. However, i n regions of h i g h l y s t r u c t u r e d c o n f u s i o n , i t i s necessary to determine the regions of the scan s u i t a b l e f o r ba s e l i n e f i t t i n g . In the smoothed data, with the high frequency noise f i l t e r e d out, t h i s can be accomplished by 78 examining the f i r s t d i f f e r e n c e a r r a y , D ( i ) = T ( i + 1 ) - T ( i ) . Since the high frequency noise power has been g r e a t l y attenuated by c r o s s - c o r r e l a t i o n , D ( i ) should be l a r g e only i n regions c o n t a i n i n g a r a p i d l y changing s i g n a l . In p r a c t i c e , i t was found that a c u t - o f f of about twice the one sigma noise l e v e l in the unsmoothed data was s u f f i c i e n t to d e l i m i t regions where s i g n i f i c a n t s t r u c t u r e appear in a scan. A f t e r b a s e l i n e removal, the data i n each scan are searched f o r extrema. For t h i s purpose, the f i r s t d i f f e r e n c e a r r a y i s again a powerful t o o l , s i n c e every extremum in the data corresponds to a zero c r o s s i n g i n the f i r s t d i f f e r e n c e . P o s i t i v e and negative extrema are d i s t i n g u i s h e d by the d i r e c t i o n of the zero c r o s s i n g . T h i s technique e s s e n t i a l l y d e t e c t s every e x c u r s i o n of the s i g n a l ; a s u b s t a n t i a l f r a c t i o n of which w i l l be low l e v e l noise peaks, or peaks in the f i n e l y s t r u c t u r e d e x t r a g a l a c t i c c o n f u s i o n background. However, without knowledge of the l o c a l b a s e l i n e l e v e l , the s t a t i s t i c a l s i g n i f i c a n c e of each peak cannot be a s c e r t a i n e d from the measured amplitude. Instead, i t i s more a p p r o p r i a t e to measure the peak to peak amplitude of p a i r s of p o s i t i v e and negative peaks that are p o s s i b l y components of a f u l l i n s t r u m e n t a l p r o f i l e . T h i s amplitude i s , to f i r s t order, independent of the l o c a l b a s e l i n e l e v e l . Each p o s i t i v e and negative p a i r , having r e l a t i v e p o s i t i o n that i s c o n s i s t e n t with an i n s t r u m e n t a l p r o f i l e , and having peak to peak amplitude g r e a t e r than 6 times the rms noise l e v e l , i s flagged as a p o s s i b l e source d e t e c t i o n . The t o l e r a n c e l e v e l f o r d e v i a t i o n s of the peak s e p a r a t i o n from 79 the known beam s e p a r a t i o n i s 3 arc-minutes. T h i s value i s d e r i v e d from the Monte C a r l o s i m u l a t i o n s d e s c r i b e d i n s e c t i o n IV.4, and i s equal to three times the one sigma s c a t t e r i n measured peak s e p a r a t i o n s f o r a r t i f i c i a l sources at lowest s i g n a l to noise r a t i o . The a n a l y s i s , to t h i s p o i n t , p r o v i d e s a set of detected s i g n a l s that c r u d e l y match the ins t r u m e n t a l response to an unresolved source. Simply put, a l l double peaked s i g n a l s with peak to peak amplitude g r e a t e r than 6a, and with r e l a t i v e peak p o s i t i o n s equal w i t h i n t o l e r a n c e t o that of the in s t r u m e n t a l p r o f i l e , have been fl a g g e d as p o s s i b l e r a d i o source d e t e c t i o n s . The remainder of the a n a l y s i s c o n s i s t s of examining the region of each d e t e c t i o n and t e s t i n g the s i g n a l to f i l t e r out spurious d e t e c t i o n s . The slope and l e v e l of the b a s e l i n e in the region of each d e t e c t i o n i s determined by a l i n e a r , l e a s t squares f i t to the data in two 5 ' segments separated by the width of an inst r u m e n t a l p r o f i l e and cen t e r e d on the p o s i t i o n of the det e c t e d s i g n a l . The b a s e l i n e i s su b t r a c t e d , and the amplitude and p o s i t i o n of each peak i s r e c a l c u l a t e d by q u a d r a t i c i n t e r p o l a t i o n using the three data samples that span the peak of each beam response. The s e p a r a t i o n of the peaks i s rechecked and the d e t e c t i o n i s d i s c a r d e d i f the b a s e l i n e removal has moved the s e p a r a t i o n o u t s i d e of the t o l e r a n c e range. With a knowledge of the l o c a l b a s e l i n e , l e v e l the s i g n i f i c a n c e of the d e t e c t i o n i s r e - e v a l u a t e d , t a k i n g i n t o 80 c o n s i d e r a t i o n both r e c e i v e r noise and the co n f u s i o n s i g n a l i n the r e g i o n of the d e t e c t i o n . An estimate of the c o n f u s i o n s i g n a l i s given by the r e s i d u a l of the l i n e a r f i t to the l o c a l b a s e l i n e (a^),. T h i s r e s i d u a l r e s u l t s from a combination of the r e c e i v e r n o i s e , e x t r a g a l a c t i c c o n f u s i o n and any g a l a c t i c c o n f u s i o n s t r u c t u r e i n the region of the d e t e c t i o n . Because of the l i m i t e d l e n g t h of the segments over which the b a s e l i n e i s measured ( 5 ' ) , ab samples only a p o r t i o n of the s p a c i a l frequency components of the t o t a l v a r i a n c e of the data. In the absence of g a l a c t i c c o n f u s i o n s t r u c t u r e , i t was found that <rb2 i s one—half of the expected v a r i a n c e due to r e c e i v e r noise and the estimated e x t r a g a l a c t i c c o n f u s i o n l e v e l of 2 mK. Since, f o r the survey o b s e r v a t i o n s , the r e c e i v e r noise i s e i t h e r much gr e a t e r than, or the same order as, the e x t r a g a l a c t i c c o n f u s i o n s i g n a l , the t o t a l data v a r i a n c e i s taken to be; cT2= tfn 2+cb2 . (IV. 1 ) The i n c l u s i o n of the b a s e l i n e term pro v i d e s an i n d i c a t o r of s i g n i f i c a n t g a l a c t i c c o n f u s i o n s t r u c t u r e . In the absence of g a l a c t i c c o n f u s i o n , the 20% o v e r e s t i m a t i o n of the v a r i a n c e , f o r cases where the r e c e i v e r n o i s e i s much greater than the e x t r a g a l a c t i c c o n f u s i o n s i g n a l , i s an e r r o r on the side of c a u t i o n and lends a d d i t i o n a l c r e d i b i l i t y to the d e t e c t i o n . A d e t e c t i o n i s d i s c a r d e d i f the peak to peak d e f l e c t i o n i s l e s s than 6cj, or e i t h e r peak i s l e s s than 2<tj. Although, alone, a 2c peak has low s t a t i s t i c a l s i g n i f i c a n c e , the Sc peak to peak l i m i t ensures that the a s s o c i a t e d peak occurs at the 4 * l e v e l . The p r o b a b i l i t y of two such peaks o c c u r r i n g , by chance, with 81 the proper p o s i t i o n a l relationship, i s low enough to j u s t i f y passing the signal to the next l e v e l of tests. For each detection, a confidence c r i t e r i o n , c a l l e d a figure of merit, i s calculated. This quantity i s a measure of the s i m i l a r i t y of the shape of the signal to a f u l l instrumental p r o f i l e with the same r e l a t i v e peak strengths. The figure of merit i s expressed in percent, and i s calculated in such a manner that, in the absence of noise, a value of 100% corresponds to an exact matching of the signal and the instrumental p r o f i l e . The expression for the figure of merit is given by equation IV.2; FM=100- [ 1-l(Tj -k-P.. )/ET. ], (IV. 2) i i 1 where Tj represents the unsmoothed data, with a l o c a l baseline removed, comprising the detected signal, Pj represents the f u l l instrumental p r o f i l e , and k i s a constant that scales the p r o f i l e to the same peak to peak deflection as the si g n a l . The summation i s carried out over the width of an instrumental p r o f i l e , which is defined as the interval between the -10 db le v e l in the outer portion of each peak. The dependence of the figure of merit on the signal to noise r a t i o for a true unresolved source signal was determined by a Monte Carlo simulation (see section IV 4.). Unless the detected signal exhibits v a r i a b i l i t y , the figure of merit must be above the l i m i t shown by the dashed curve in figure 33 to be accepted as a compact source detection. As a f i n a l precaution, the unsmoothed shape of the largest peak of each detection is f i t by a gaussian. In t h i s way, 82 spurious source p r o f i l e s a r i s i n g from strong, narrow spikes i n the raw data that have been broadened, as a r e s u l t of the c r o s s - c o r r e l a t i o n , to a good approximation of the beams, are dete c t e d and d i s c a r d e d . The gaussian f i t a l s o p r o v i d e s the best measure of the angular diameter of the source, given by equation IV.3, where 4>m i s the measured HPBW, # p i s the ins t r u m e n t a l HPBW, and f i s a f a c t o r which accounts f o r the noise broadening of the beams (see f i g u r e 29). 3.2 Spurious and Extended Sources The t e s t s of the source s i g n a l , d e s c r i b e d i n the previous s e c t i o n , are aimed at p r e c l u d i n g noise peaks from the p r e l i m i n a r y catalogue of compact sources. However, i n regions where the survey i s co n f u s i o n l i m i t e d , c o n f u s i o n generated spurious source p r o f i l e s may have s u f f i c i e n t s i g n a l to noise r a t i o to be i n c l u d e d . To produce the f i n a l catalogue of compact r a d i o sources, these spurious p r o f i l e s must be i d e n t i f i e d and d i s c a r d e d . The g a l a c t i c and e x t r a g a l a c t i c c o n f u s i o n s i g n a l s have d i s t i n c t l y d i f f e r e n t p r o p e r t i e s . G a l a c t i c c o n f u s i o n i s r e l a t i v e l y strong, c o n f i n e d to s p e c i f i c r egions and organized i n s t r u c t u r e ; whereas, e x t r a g a l a c t i c c o n f u s i o n i s weak, i s o t r o p i c and e s s e n t i a l l y random in s t r u c t u r e . Because of these d i f f e r e n c e s , i t i s convenient, f o r the purpose of d e t e c t i n g spurious s i g n a l s , to con s i d e r the e f f e c t s of the two types of c o n f u s i o n s i g n a l s independently. Diam (IV.3) 83 The f i g u r e of merit t e s t of the source p r o f i l e s e f f e c t i v e l y l i m i t s d e t e c t i o n s with high s i g n a l to noise r a t i o to sources with angular extent of l e s s than about 6', p a r a l l e l to the scan. However, t h i s t e s t i s one dimensional, i n the sense that i t i s c a r r i e d out on the s i g n a l i n only one scan, and f i l a m e n t a r y s t r u c t u r e , or sources that are extended p r i m a r i l y i n d i r e c t i o n s at l a r g e angles to the scan, w i l l produce p r o f i l e s that are i n d i s t i n g u i s h a b l e from that of an unresolved source. To d e t e c t t h i s e f f e c t a two-dimensional view of the data i s produced by c o n s t r u c t i n g beam switched maps of the survey r e g i o n . The software to produce these maps was developed at the U n i v e r s i t y of B r i t i s h Columbia by Dr. P.C. Gregory and M.A. P o t t s . The maps are obtained by p l o t t i n g the antenna temperature of each data sample i n a scan above a l i n e d e f i n e d by the t e l e s c o p e c o - o r d i n a t e s at the time of each sample. S i g n a l s that a r i s e from extended g a l a c t i c s t r u c t u r e are e a s i l y i d e n t i f i e d on these maps. A sample map that i n c l u d e s a h i g h l y confused region of the plane i s shown i n f i g u r e 24. For comparison, a region of the plane, i n which no g a l a c t i c c o n f u s i o n s t r u c t u r e i s e v i d e n t , i s shown i n f i g u r e 25. To provide s u f f i c i e n t dynamic range to show both strong s i g n a l s and weak s i g n a l s , of about 10 mK, a l o g a r i t h m i c temperature s c a l e i s used. The region of each d e t e c t i o n i n the p r e l i m i n a r y source l i s t i s examined v i s u a l l y on the beamswitched maps, and d e t e c t i o n s a s s o c i a t e d with confused s t r u c t u r e are d i s c a r d e d . T h i s procedure r e s u l t s in the e f f e c t i v e d e l e t i o n of three 84 85 111111111111111111111111111 [ 11111111111111111111111111111111111111111 [ 1111111 21-56- h T no 1 1 1 1 ' 1 1 1 1 1 1 1 1 1 1 1 1. 1 1 1 1 1 1 1 • • 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 51° 52° 53' 54° DECLINATION 55* 56" Figure 25. A beam-switched map of a region no ga lact ic confusion structure of the plane in which is evident. 86 s e c t i o n s of the g a l a c t i c plane from the survey r e g i o n . These areas i n c l u d e the inner 15 degrees of l o n g i t u d e of the survey 40°<1<55 C, the Cygnus region 78°<1<86° and the l o n g i t u d e i n t e r v a l 111°<1<114°, which corresponds to the d i r e c t i o n of the Perseus arm of the galaxy. In these areas the high l e v e l of c o n f u s i o n , extending over the e n t i r e l e n g t h of the scan f o r a number of c o n s e c u t i v e scans, renders the i d e n t i f i c a t i o n of u n d e r l y i n g , unresolved source p r o f i l e s i m p o s s i b l e . Outside of these areas strong c o n f u s i o n s t r u c t u r e occurs i n r e s t r i c t e d r e g i o n s , a f f e c t i n g only a p o r t i o n of a scan and extending over only a few scans. Approximately 30% of the p r e l i m i n a r y sources were d i s c a r d e d due to a s s o c i a t i o n with g a l a c t i c c o n f u s i o n . The remainder of the high s i g n a l to noise d e t e c t i o n s r e s u l t from i s o l a t e d compact source s i g n a l s . Spurious s i g n a l s a r i s i n g from the e x t r a g a l a c t i c c o n f u s i o n background occur only at very low l e v e l s . Measurements of the s i g n a l l e v e l in scans i n which no s t r u c t u r e i s e v i d e n t , and no sources are d e t e c t e d , i n d i c a t e that the e x t r a g a l a c t i c c o n f u s i o n s i g n a l has an rms of about 2—3 mK. Thus, only average scans comprised of more than f i v e o b s e r v a t i o n s with both r e c e i v e r s , w i l l be e x t r a g a l a c t i c c o n f u s i o n l i m i t e d . T h i s i n c l u d e s a l l of the 1977 data base, and 40% of 1978. Because of the e s s e n t i a l l y random s t r u c t u r e of e x t r a g a l a c t i c c o n f u s i o n , which a r i s e s from the s u p e r p o s i t i o n of responses from the background of d i s t a n t e x t r a g a l a c t i c sources, the method of examining each p r o f i l e d e t e c t e d f o r c o r r e l a t i o n with the c o n f u s i o n s t r u c t u r e i s not f e a s i b l e in t h i s case. 87 However, the random nature of the signal lends i t s e l f to a s t a t i s t i c a l approach. Spurious signals with the approximate shape of an instrumental p r o f i l e , that are generated by this confusion background, w i l l be produced with equal probability with the sense of the beams reversed, as with the proper orientation. Therefore, to determine the magnitude of the problem, a search for compact sources was ca r r i e d out on the 1977 data; searching for signals in which the order of the beam response i s opposite to the true instrumenal p r o f i l e . After discarding p r o f i l e s that are associated with strong galactic confusion, and signals below the figure of merit l i m i t , a population of weak signals remain. This population is compared to the results of the proper 1977 compact source search in figure 26. The curves show the number of detections with peak to peak deflection less than D p p, as a function of D p p. It i s obvious from the curves that, below a peak to peak of about 8 mK, signals with proper, and signals with improper, beam orientation are produced with equal p r o b a b i l i t y . For D p p between 8 and 12 mK, spurious signals s t i l l occur, but the excess of proper orientation detections indicate that a frac t i o n of these sources are r e a l . At 12 mK, approximately 30% of the proper detections are r e a l . Above 12 mK very few spurious detections occur. At any peak to peak signal l e v e l , the curves in figure 26 allow the probability that a signal represents a real source to be calculated, but, on an individual basis, i t i s impossible to determine which signals are r e a l . Thus, in order to ensure 88 1 i 1 1 70 T _f • _l r i 6 0 _i i r ' I i 5 0 r i i i 1 _r i -1 o 4 0 V, i j j i r r r ' -z 1 1 r 1 3 0 rJ" 1—' 1 2 0 -1 f 1 1 1 [ ) l~ I <* H 1 1 1 (J I r -' 1 1 , «-« -1 0 i i rr j 1 i — _i j -J • 1 . 1 5 1 0 15 2 0 Peak to Peak Deflection (mK) Figure 26. The rate of spurious signal detections. The so l i d l i ne i s the number of spurious detect ions, with peak to peak def lect ion less then Dpp, resu l t ing from a search of the 1977 data for signals with the pos i t ive and negative peak posit ions reversed. The dashed l i ne i s the same quantity fo r the results of the proper 1977 compact source search. 89 that no spurious s i g n a l s are i n c l u d e d in the f i n a l source c a t a l o g u e , a l l d e t e c t i o n s with peak to peak d e f l e c t i o n below 12 mK should be ignored. However, to f i r s t order, the background c o n f u s i o n s i g n a l i s n o n - v a r i a b l e , and, s i n c e the primary goal of t h i s survey i s to d e t e c t v a r i a b l e sources, each d e t e c t i o n i s f i r s t measured for v a r i a b i l i t y (see s e c t i o n V 1.). Only those d e t e c t i o n s with peak to peak below 12 mK, that show no evidence for v a r i a b i l i t y , are precluded from the f i n a l compact source c a t a l o g u e . In a d d i t i o n to spurious s i g n a l s generated d i r e c t l y by c o n f u s i o n , spurious s i g n a l s may a l s o a r i s e as a r e s u l t of the s i d e — l o b e l o c a t e d 5 arc—minutes west of the beam peaks. The —15 db s i d e — l o b e w i l l produce a s o u r c e — l i k e s i g n a l with a peak s t r e n g t h g r e a t e r than 10 mK i f the t e l e s c o p e i s scanning 5 arc—minutes east of a source with s t r e n g t h g r e a t e r than 350 mK. For the three most eastward scan sequences, these spurious s i g n a l s can be i d e n t i f i e d i n r e l a t i o n to strong sources d e t e c t e d in the adjacent scans. In such cases, the s i g n a l s are d i s c a r d e d . However, in the two most westward sequences (sequence 4 and 5), spurious s i g n a l s may be produced by strong s t r u c t u r e o u t s i d e of the observing area. In t h i s case, the s i g n a l s cannot be i d e n t i f i e d as products of the s i d e — l o b e . An estimate of the expected number of such s i g n a l s can be obtained from the d e n s i t y of strong s i g n a l s found i n the o b s e r v a t i o n s . Within the area covered by the o b s e r v a t i o n s , 31 s t r u c t u r e s with s t r e n g t h g r e a t e r than 350 mK were d e t e c t e d . The number decreases at l a r g e r s t r e n g t h s to 5 at 1000 mK. For 90 a source with a s t r e n g t h of 350-1000 mK to be undetected by the survey, yet produce a d e t e c t a b l e s i g n a l i n a survey scan v i a the s i d e — l o b e , i t must be s i t u a t e d w i t h i n 4 arc-minutes west of sequence 5. The area w i t h i n t h i s region equals 31% of the area covered by the survey o b s e r v a t i o n s . T h e r e f o r e , strong s t r u c t u r e s o u t s i d e of the survey area are expected to produce about 10 s i g n a l s with s t r e n g t h in the range 10-30 mK, i n sequences 4 and 5. The m a j o r i t y of the s i g n a l s w i l l l i e at the low end of t h i s range; only one or two are expected at the 30 mK l e v e l . In sequences 4 and 5, the minimum r e c e i v e r noise l e v e l i s 2.4 mK. Thus, a 10 mK s i g n a l s has a 50% p r o b a b i l i t y of being detected (see f i g u r e 27), and the d e t e c t i o n p r o b a b i l i t y i s 75% at 20 mK. Consequently, about 6 of the 10 s i d e — l o b e s i g n a l s w i l l be d e t e c t e d . T h i s i s a small f r a c t i o n (*1%) of the number of sources d e t e c t e d i n the survey r e g i o n . A n a l y s i s of the complete survey data (sequences 1 to 14) w i l l r e v e a l the s t r u c t u r e p r e s e n t l y o u t s i d e of the observing r e g i o n , and allow these spurious d e t e c t i o n s to be i d e n t i f i e d . 3.3 E s t i m a t i o n of Source P o s i t i o n and Strength The observed c o - o r d i n a t e s of each source are given by a combination of the p o s i t i o n of the source response i n the scan and the c a l c u l a t e d o f f s e t of the source from the c e n t r a l t r a c k of the scan. The p o s i t i o n i n the scan i s d e f i n e d as the d i r e c t mean of the p o s i t i o n of the two peaks on the source p r o f i l e , and corresponds to the p o s i t i o n of the p r o j e c t i o n on the c e l e s t i a l sphere of the c e n t r e of the feed box (see s e c t i o n III 91 3.) at the time of c l o s e s t approach to the source. The co-o r d i n a t e s of t h i s p o i n t are determined by i n t e r p o l a t i n g l i n e a r l y between the 1950 s t a r t and end c o - o r d i n a t e s of the scan. The o f f s e t of the source i s the d i s t a n c e of c l o s e s t approach of the source to the c e n t r a l scan t r a c k , and i s uniquely d e f i n e d by the r a t i o of the response produced by the source i n each beam. From the models of the East-West beam p r o f i l e s (equation 111 . 1 ) , the r a t i o (R) of peak A to peak B can be expressed as R(e)=R 0-[P(x„,c a)/P(x b,c b)] . (IV.4) Here, P(x,c) i s given by equation I I I . 1 , and x a = (©~e 0) / H W a a n (3 x b=(e+9 0)/HW b, where e i s the o f f s e t of the source and © 0 i s the- a b s o l u t e value of the o f f s e t of the peaks of the beams. The constants c a and c b are the d e c l i n a t i o n dependent beam model parameters, and R 0 i s the peak r a t i o at zero o f f s e t , given by the gain r a t i o of the beams. The raw peak stren g t h s of the source s i g n a l are d e r i v e d from the smoothed data by c o r r e c t i n g for the e f f e c t s of smoothing with a 3' beam. Since, f o r the m a j o r i t y of the sources, the estimated angular diameter (equation IV.3) i s very i n a c c u r a t e , no attempt has been made to c o r r e c t the peak str e n g t h s f o r sources that are p o s s i b l y s l i g h t l y r e s o l v e d . The c o r r e c t i o n f o r smoothing i s c a l c u l a t e d with the assumption that the source p r o f i l e i s given by the North—South ins t r u m e n t a l p r o f i l e . For t h i s purpose, the beams are approximated by simple gaussians, f o r which the a t t e n u a t i o n due to smoothing i s given by, [ 1 + U / 3 ) 2 ]" °'5. 92 I n v e r t i n g equation (IV.4) y i e l d s a m u l t i - v a l u e d s o l u t i o n f o r e as a f u n c t i o n of R . T h i s r e s u l t i s an a r t i f a c t of the beam model; a l l but one of the s o l u t i o n s o c c u r r i n g o u t s i d e of the range of a p p l i c a t i o n of the model. The a c t u a l o f f s e t f o r each source i s c a l c u l a t e d by s o l v i n g equation IV.4 n u m e r i c a l l y , using an i t e r a t i v e procedure c o n f i n e d to the v a l i d range of the model. The r i g h t ascension and d e c l i n a t i o n components of the c a l c u l a t e d o f f s e t are added to the c o - o r d i n a t e s of the scan p o s i t i o n of the source s i g n a l to a r r i v e at the observed co-o r d i n a t e s of the source. From the gain of each beam at the o f f s e t of the source the source s t r e n g t h can be c a l c u l a t e d . The source s t r e n g t h K i s d e f i n e d as the peak antenna temperature of the beam A response of an i d e n t i c a l source p a s s i n g d i r e c t l y through the center of beam A. That i s , the peak A antenna temperature of an i d e n t i c a l source with o f f s e t equal to e 0 . The peak to peak response of a source of s t r e n g t h K s , as a f u n c t i o n of o f f s e t i s , P P = K S [ G Q ( e ) + G b ( e ) / R 0 ] , (IV.5) where G a ( e ) and G b ( e ) are the normalized gains of beams A and B r e l a t i v e to the peak, given by equation 111 . 1 - Since the accuracy of the beam models decreases with d i s t a n c e from the beam peak (see f i g u r e 22), f o r any value of 0, the l a r g e r of G a ( e ) or G b ( e ) w i l l be known, with g r e a t e r p r e c i s i o n . T h i s e f f e c t i s p a r t i c u l a r l y important at l a r g e o f f s e t , when the source i s 1.4 arc-minutes c l o s e r to one beam than the other. T h e r e f o r e , i n c a l c u l a t i n g the source s t r e n g t h one of two forms 93 of equation IV.5 i s used: R>1, K s=PP/[G a(1+1/R)] (IV.6) R<1, K s=R 0.PP/[G b(l+R)] The e r r o r s on the source s t r e n g t h and o f f s e t are c a l c u l a t e d based on the v a r i a n c e i n the data given by equation IV.1. The q u a n t i t y aj i s c a r r i e d through the q u a d r a t i c i n t e r p o l a t i o n of the three data p o i n t s about each peak to a r r i v e at <sQ and « b , the e r r o r s on the peak valu e s P Q and P5 of beam A and B, r e s p e c t i v e l y . The e r r o r s on the beam r a t i o and peak to peak d e f l e c t i o n are then, * r = y [ < r a 2 + ( R . f f b ) 2 ] / P b (IV.7) 'pp=y*a2 +tfb2 and the e r r o r on the o f f s e t and source s t r e n g t h are, c0 = y(de/dR) 2cr2 (IV.8) <rR = / ( K s /PP) 2 • <rp2p+ [ Ks /( 1 +R) ] 2 • * 2 The q u a n t i t y de/dR i s c a l c u l a t e d n u m e r i c a l l y , at © equal to the o f f s e t of the source. 4. Monte C a r l o Simulations From the o r i g i n a l raw scan s i g n a l to the p r e l i m i n a r y l i s t of compact r a d i o sources, p r o c e s s i n g of the data i s c a r r i e d out e n t i r e l y by computer. This approach i s necessary, because of the vast q u a n t i t y of data i n v o l v e d , and d e s i r a b l e , because of the consequent u n i f o r m i t y i n the treatment of the data. •-( 94 However, the p r o p e r t i e s of t h i s complex i n t e r f a c e between the raw data and the r e s u l t s , are another f a c t o r to be c o n s i d e r e d when i n t e r p r e t i n g the r e s u l t s . In essence, i t becomes necessary to c a l i b r a t e the r e d u c t i o n program. T h i s i s done by t r e a t i n g the program as a black box and measuring the response to c o n t r o l l e d i n p u t . Since the number of source d e t e c t i o n s i n c r e a s e s with d e c r e a s i n g f l u x d e n s i t y , i t i s p a r t i c u l a r l y important to i n v e s t i g a t e the response of the program to low s i g n a l to noise i n p u t . Monte C a r l o type s i m u l a t i o n runs were c a r r i e d out on the compact source search program t o : 1) determine the e f f i c i e n c y of the search, 2) measure the accuracy of the s i g n a l parameter estimates and check f o r any systematic e f f e c t s i n troduced by the r e d u c t i o n method, and 3) to determine the ac c e p t a b l e d e v i a t i o n s from expected values, f o r t e s t of the detected s i g n a l s (eg. peak separation) before i n c l u s i o n in the f i n a l c a t a l o q u e . For these purposes, i t i s convenient to c l a s s i f y measurements of the s i g n a l p r o p e r t i e s i n t o two types; those that measure p r o p e r t i e s of the i n d i v i d u a l beams of the p r o f i l e , such as the peak s t r e n g t h , p o s i t i o n and HPBW; and those that measure the p r o p e r t i e s of the s i g n a l as a whole, such as the f i g u r e of merit and the rms d a i l y v a r i a t i o n i s the s i g n a l . (This l a t t e r i s d i s c u s s e d i n d e t a i l i n s e c t i o n V 1.3, and i s mentioned here only f o r completeness.) The source d e t e c t i o n e f f i c i e n c y i s a measurement in the f i r s t c l a s s , s i n c e each peak of the p r o f i l e must be det e c t e d independently. I t i s obvious that the f i r s t c l a s s of measurements are a f f e c t e d by the s i g n a l 95 to noise r a t i o i f a s i n g l e peak, and the second c l a s s by the s i g n a l to noise r a t i o of the complete p r o f i l e (peak to peak). Two s i m u l a t i o n runs were c a r r i e d out, the f i r s t r e l a t i n g to the f i r s t c l a s s of s i g n a l parameters. A r t i f i c i a l source p r o f i l e s with equal p o s i t i v e and negative peak s t r e n g t h s were c o n s t r u c t e d , using the North-South beam model, and i n s e r t e d i n t o the average scans of the 1979 o b s e r v a t i o n s . One a r t i f i c i a l source was i n s e r t e d i n t o each scan. The p o s i t i o n of each i n s e r t i n the scan was chosen at random using a pseudo-random number generator. The peak s t r e n g t h s were, l i k e w i s e , chosen randomly i n 10 mk i n t e r v a l s i n the range 10 to 100 mK. A t o t a l of 617 a r t i f i c i a l p r o f i l e s were i n s e r t e d i n t o the data, y i e l d i n g about 60 i n s e r t s at each peak s t r e n g t h . However, for t h i s a n a l y s i s , the r e l e v a n t v a r i a b l e i s the s i g n a l to noise r a t i o . In 1979, the noise l e v e l in the average scan ranges from 1.9 mK to 4.8 mK, depending on the scan sequence. Thus, t a k i n g i n t o account the 30% r e d u c t i o n in the peak l e v e l due to smoothing, the peak s i g n a l to noise r a t i o of the i n s e r t s ranges from 1.5 to 36.8. > F i g u r e 27 shows the source d e t e c t i o n e f f i c i e n c y as a f u n c t i o n of peak s i g n a l to noise r a t i o . The d e t e c t i o n e f f i c i e n c y i s d e f i n e d , simply, as the r a t i o of the number of i n s e r t s detected to the t o t a l number i n s e r t e d i n a given s i g n a l to noise b i n . The e f f i c i e n c y remains g r e a t e r than 95% down to a peak s i g n a l to noise r a t i o of 12. The approximate 5% l o s s e s fo r s i g n a l to noise r a t i o g r e a t e r than 12, r e s u l t from i n s e r t s i n t o regions where the l e v e l of g a l a c t i c c o n f u s i o n s t r u c t u r e 96 I.Of-u c a> ]o H — LU u O 0.5 I : i j i i L_ 5 10 15 20 25 Peak Signal to Noise Ratio Figure 27. Source detection e f f i c i ency as a function of peak signal to noise r a t i o . 97 masks the source p r o f i l e . Below a value of 12*, the e f f e c t s of r e c e i v e r noise reduce the d e t e c t i o n e f f i c i e n c y to about 75% at le, and 50% at 3.5<y. The d e t e c t i o n c u t - o f f c r i t e r i o n , f o r the peak to peak s i g n a l , of s i x times the rms noise l e v e l (see s e c t i o n IV 3.1), which corresponds to 3a peak s i g n a l to noise f o r p r o f i l e s with a beam r a t i o of one, produces the d e t e c t i o n e f f i c i e n c y of zero below t h i s v a l u e . Because of the non-urfif ormity of the r e c e i v e r n o i s e between scan sequences, the v a r i a t i o n of the t e l e s c o p e s e n s i t i v i t y with both d e c l i n a t i o n and the o b s e r v i n g s e s s i o n , and the o f f s e t dependence of the amplitude of a source response, the d e t e c t i o n e f f i c i e n c y of the survey in terms of f l u x d e n s i t y i s an i l l - d e f i n e d q u a n t i t y . However, as a rough i n d i c a t i o n of the survey s e n s i t i v i t y ; for a source s i t u a t e d on the c e n t r a l scan t r a c k , in the worst case of an average scan comprised of o b s e r v a t i o n s with one r e c e i v e r and a t o t a l of s i x scans (sequences" 4 and 5 i n 1979), a 17 mJy source i s r e q u i r e d to produce a 3.5u peak d e f l e c t i o n at a d e c l i n a t i o n of 60° (where the m a j o r i t y of the survey o b s e r v a t i o n s o c c u r ) . In the best case, two r e c e i v e r s and 20 o b s e r v a t i o n s (sequence 1 i n 1977), 3.5«r corresponds to 7 mJy. Thus, fo r a source with zero o f f s e t , the f l u x d e n s i t y corresponding to 50% d e t e c t i o n e f f i c i e n c y ranges from 7 mJy to 17 mJy. F i g u r e s 28 to 30 show the s i m u l a t i o n r e s u l t s f o r the measured p o s i t i o n s , s t r e n g t h s and h a l f - w i d t h s as a f u n c t i o n of the s i g n a l to noise r a t i o of the beam peaks. The upper p o r t i o n of the f i g u r e s shows; for p o s i t i o n , the mean d i f f e r e n c e between 98 the input and output v a l u e s , AP, and, f o r st r e n g t h s and h a l f - w i d t h s , the mean percentage d i f f e r e n c e , AS/S and AH/H. The e r r o r bars represent one standard d e v i a t i o n on the mean v a l u e s . In the lower p o r t i o n of each f i g u r e , the one sigma e r r o r on a s i n g l e measurement i s shown. Smooth curves have been drawn through these p o i n t s to d e l i n e a t e the trend of the data. No systematic d i f f e r e n c e between the input and measured i n s e r t p o s i t i o n s i s e v i d e n t , and, down to a s i g n a l to noise of about 10, the p o s i t i o n s are accurate to 10". However, both the peak strengths and h a l f - w i d t h s e x h i b i t s i g n i f i c a n t systematic e f f e c t s . Peak s t r e n g t h s are overestimated by about 5% independent of the s i g n a l to noise r a t i o . T h i s overestimate may a r i s e as a r e s u l t of the gaussian approximation of the beams used to c a l c u l a t e the a t t e n u a t i o n due to smoothing. A more p r e c i s e value f o r AS i s determined from the second S s i m u l a t i o n run. Considerable broadening of the beams occurs as the s i g n a l to noise decreases. At l e the broadening i s 1 arc-minute. T h i s e f f e c t i s taken i n t o account when c a l c u l a t i n g the angular diameter of the survey sources (equation IV.3). For the second s i m u l a t i o n run, i d e n t i c a l a r t i f i c i a l source p r o f i l e s were i n s e r t e d i n t o each of the scans that comprise the average scan. T h i s method of i n s e r t i o n was employed in order to t e s t the measurement of source v a r i a t i o n s , which i s d i s c u s s e d l a t e r . The a n a l y s i s presented here r e l a t e s only to the p r o p e r t i e s of the s i g n a l in the average scan. i i — -J I ' • I L_ 10 2 0 3 0 Peak Signal to Noise Ratio Figure 28. Simulation results for measured scan pos i t ions. The mean difference between the input and output posit ions (top), and the error on a s ingle measurement (bottom), as a function of peak signal to noise r a t i o . 100 Peak Signal to Noise Ratio Figure 29. Simulation results for measured peak strengths. The mean percentage difference between input and output strengths (top), and the percent error on a s ingle measurement (bottom), as a function of peak signal to noise r a t i o . 101 Figure 30. Simulation results for measured HPBW. The mean percentage difference between input and output HPBW (top), and the error on a s ingle measurement (bottom), as a function of peak signal to noise r a t i o . 102 A r t i f i c i a l p r o f i l e s were i n s e r t e d i n t o both the 1977 and 1979 survey scans. A l l Together 430 p r o f i l e s were i n s e r t e d i n t o the data. The 1979 i n s e r t s t r e n g t h s were chosen, in the i n t e r v a l of 10 to 300 mK, i n steps of 10 mK, using a psuedo—random number generator. For 1977, where the noise l e v e l i n the average scan i s much lower, source s t r e n g t h s range up to 100 mK. The r e l a t i v e peak s t r e n g t h s of the p r o f i l e s were ad j u s t e d to simulate sources with o f f s e t s ranging from -1 to 1 minutes of a r c . F i g u r e 31 shows the output source s t r e n g t h p l o t t e d a g a i n s t input s t r e n g t h . Output stre n g t h s are c a l c u l a t e d using equation IV.6 from the measured beam r a t i o and peak to peak d e f l e c t i o n . The best f i t , s t r a i g h t l i n e to the data has a slope of 1.048±.005, c o n s i s t e n t with the 5% o v e r e s t i m a t i o n of the peak s t r e n g t h s i n d i c a t e d by the f i r s t s i m u l a t i o n run ( f i g u r e 29). Measured stre n g t h s of the survey sources are reduced by 4.8% to compensate f o r t h i s e f f e c t . The f i g u r e of merit (equation IV.2) of the i n s e r t s i s p l o t t e d as a f u n c t i o n of the peak to peak s i g n a l to noise r a t i o in f i g u r e 32. The f i g u r e of merit was designed as a d i a g n o s t i c , to a i d i n f i l t e r i n g out spurious s i g n a l s . In f i g u r e 33, the f i g u r e s of merit f o r the unresolved 1977 and 1979 survey sources, and f o r the spurious s i g n a l s d e t e c t e d as a r e s u l t of s e a r c h i n g f o r p r o f i l e s with the improper beam o r i e n t a t i o n (see s e c t i o n IV 3.2), are p l o t t e d in the same manner as the s i m u l a t i o n r e s u l t s i n f i g u r e 32. The s o l i d l i n e in f i g u r e 33 represents the mean curve through the s i m u l a t i o n 103 r e s u l t s . The s i m u l a t i o n r e s u l t s roughly d e l i n e a t e the upper envelope of the f i g u r e s of merit of the survey sources f o r D p p A n * 10. With some exceptions, the f i g u r e s of merit f o r the spurious s i g n a l s from the search f o r improper p r o f i l e s , tend to c l u s t e r at the lower end of the s c a t t e r in the survey source f i g u r e s of m e r i t . Thus, while i t i s not p o s s i b l e to completely e l i m i n a t e spurious d e t e c t i o n s based on the f i g u r e of merit alone, at l e a s t p a r t i a l f i l t e r i n g can be obtained by s u i t a b l e c h o i ce of a s i g n a l to noise dependent f i g u r e of merit l i m i t . The c hoice of t h i s l i m i t i s somewhat a r b i t r a r y . The l i m i t adopted i s shown as the dashed curve i n f i g u r e 33. The curve e l i m i n a t e s a l a r g e f r a c t i o n of the spurious s i g n a l s , but only those survey r e s u l t s at the extreme low end of the s c a t t e r . I t should be noted that these r e s u l t s are based on unresolved survey sources. Sources with measurable angular extent have reduced f i g u r e of merit due to the broader beam p r o f i l e s . The f i g u r e of merit l i m i t of 60%, at high s i g n a l to noi s e , corresponds to a c u t - o f f i n angular extent of about 6 arc-minutes. To ensure that v a r i a b l e source components of these extended sources, or v a r i a b l e sources with f i g u r e of merit reduced by co n f u s i o n to below the l i m i t , are not overlooked, s i g n a l s are r e j e c t e d only a f t e r the search f o r v a r i a b i l i t y has been c a r r i e d out. 1 04 IOO 200 300 Input Strength (mk) Figure 31. Output strength versus input strength for the a r t i f i c i a l source in se r t s . The s t ra ight l i ne f i t to the data has a slope of 1.048±.005. 105 -l 1 1 i — i i i i I 1 r- 1 1 — i — I I i | I l • # • t • ' • * i i i 1 1 1 1 — i .i i i i I 1 1 -10 100 Dpp/o-n Figure 32. Figure of merit versus peak to peak signal to noise r a t i o for the a r t i f i c i a l source inser t s . 106 • • ' 10 100 Dpp/cTn Figure 33. Figure of merit versus peak to peak signal to noise r a t i o for unresolved survey sources (dots) and the spurious s ignals from the search of the 1977 data for reversed p ro f i l e s (open c i r c l e s ) . The f igure of merit lower l i m i t for inc lus ion on the preliminary source l i s t i s shown by the dashed curve. The so l i d l i ne i s the mean curve through the simulation results (f igure 32). 107 CHAPTER V MEASUREMENT OF VARIABILITY 1. Short—term V a r i a t i o n s 1.1 Method When t h i s survey was i n i t i a t e d , i t was planned to search f o r v a r i a t i o n s o c c u r r i n g on a time s c a l e of days using a method analogous to the o p t i c a l technique of b l i n k i n g , whereby, v a r i a b i l i t y i s dete c t e d v i a modulations i n t r o d u c e d by the process of b l i n k i n g two photographs of a s t e l l a r f i e l d , taken at d i f f e r e n t epochs. With the survey data base, the b l i n k i n g would be c a r r i e d out with a computer by t a k i n g the d i f f e r e n c e between each scan and the average scan, and search i n g f o r s i g n i f i c a n t s i g n a l s in the d i f f e r e n c e scans. However, t h i s method proved to be i m p r a c t i c a l , due to small f l u c t u a t i o n s in the d e c l i n a t i o n p o i n t i n g from day to day. These f l u c t u a t i o n s , r e s u l t i n g from small v a r i a t i o n s i n the d r i v e r a t e d u r i n g a scan, produce peak to peak changes i n the p o s i t i o n of a source along the scan, from one day to another, of up to two scan samples (52"). T h i s i s a s i g n i f i c a n t f r a c t i o n of the HPBW of the i n s t r u m e n t a l p r o f i l e . Consequently, d i r e c t d i f f e r e n c i n g of each scan from the average y i e l d s a r e s i d u a l s i g n a l which, f o r po i n t sources, has an rms of 10% to 20% of the average s i g n a l . T h i s r e s i d u a l s i g n a l not only imposes a l a r g e l i m i t on the s e n s i t i v i t y of the survey to v a r i a b i l i t y , but, i n the case of measurable v a r i a t i o n s , s e v e r e l y d i s t o r t s the instr u m e n t a l response i n the d i f f e r e n c e scan, which f u r t h e r degrades the 108 accuracy of the v a r i a b i l i t y measurements. Because of these e f f e c t s , the a l t e r n a t e method of s imply measuring the d a i l y f l u x d e n s i t y of a l l sources detected i n the average data was adopted. To ob ta in maximum s i g n a l to noise r a t i o i n the measurement of the d a i l y s i g n a l l e v e l of each source , an in s t rumenta l p r o f i l e i s cons t ruc ted that matches the parameters of the s i g n a l produced by the source i n the average scan. Th i s p r o f i l e i s cross—correlated w i t h the da ta , at the scan p o s i t i o n of the source , i n each of the scans which comprise the average scan . Before c r o s s - c o r r e l a t i o n a l o c a l b a s e l i n e i s removed i n an i d e n t i c a l manner to that used on the average data dur ing the compact source search (see s e c t i o n IV 3 . 1 ) . The c r o s s -c o r r e l a t e d s i g n a l Xj i s c a l c u l a t e d us ing equat ion V.1. x i ; ] ( T i + K " * i ) , ( p j " F ) where, ( V .1) T | = ] T U j - i . a n d ? = J P J In these e x p r e s s i o n , i 0 i s the scan element at which the summation beg ins , and i s equal to the scan p o s i t i o n of the source in the average scan minus h a l f the width of a f u l l in s t rumenta l p r o f i l e . The s u b s c r i p t e d T and P i n equations V .1 represent , r e s p e c t i v e l y , the smoothed antenna temperature at the s u b s c r i p t scan p o s i t i o n and the amplitude of the j t n element of the smoothed in s t rumenta l p r o f i l e . S u b t r a c t i o n of the means, Tj and P, removes the e f f e c t s of u n c e r t a i n t i e s in the DC 109 b a s e l i n e l e v e l from the c r o s s - c o r r e l a t i o n r e s u l t s . The s i g n a l l e v e l f o r each o b s e r v a t i o n i n given by the maximum value (X m) of the c r o s s - c o r r e l a t i o n f u n c t i o n , which i s measured by q u a d r a t i c i n t e r p o l a t i o n using the three values spanning the c r o s s - c o r r e l a t e d peak. D a i l y p o i n t i n g f l u c t u a t i o n s along the scan have no e f f e c t s i n c e the p o s i t i o n of the peak of the c r o s s - c o r r e l a t i o n f u n c t i o n i s measured independently f o r each o b s e r v a t i d n . The values X m are converted to a measure of the source s t r e n g t h (K ) using a n o r m a l i z a t i o n f a c t o r which i s equal to the r a t i o of the source s t r e n g t h i n the average scan, ( K s ) , (equation IV.6), to the mean amplitude of the c r o s s - c o r r e l a t i o n peaks ( X m ) . Th i s method of measuring the d a i l y f l u x d e n s i t y of a v a r i a b l e s i g n a l was t e s t e d by i n s e r t i n g a r t i f i c a l v a r i a b l e sources i n t o a small number of survey scans. The s i g n a l p r o f i l e s were generated with v a r i o u s peak r a t i o s to simulate d i f f e r e n t o f f s e t s from the c e n t r a l t r a c k , and a v a r i a b l e source was c r e a t e d by s c a l i n g the p r o f i l e s with a randomly v a r y i n g s c a l i n g f a c t o r . These p r o f i l e s were i n s e r t e d i n t o the i n d i v i d u a l scans p r i o r to c r e a t i n g the average and the data were run through the r e d u c t i o n program. In a l l cases, the measured d a i l y source s t r e n g t h s were i d e n t i c a l to the input v alues to w i t h i n the e r r o r produced by the r e c e i v e r noise i n a s i n g l e scan. A measure of the v a r i a b i l i t y of the source i s obtained by c a l c u l a t i n g the f r a c t i o n a l rms v a r i a t i o n ( f v = t f v / X m ) of the amplitude of the i n d i v i d u a l c r o s s — c o r r e l a t e d peaks, X m, about 1 10 the mean. As discussed in the next two sections, the combined eff e c t s of instrumental variations and receiver noise produce an expected rms f r a c t i o n a l v a r i a t i o n ( f e ) that can be expressed as a function of the peak to peak source sig n a l . It is convenient, then, to define as a v a r i a b i l i t y index the r a t i o of the measured, to expected, one sigma va r i a t i o n , V•t = ty./te. This index is e f f e c t i v e in detecting v a r i a b i l i t y among sources that exhibit continuous variations. However, the contribution to * v from a variation measured in a single observation decreases as 1 /y/n~ , for a t o t a l of n observations. Consequently, for sources that are variable only a small fraction of the time, V, may considerabley underestimate the degree of v a r i a b i l i t y of the source. Therefore, for each source, a second v a r i a b i l i t y index, V 2, defined by equation V.2 is calculated. v 2 = (K - K s ) m a x / ( f e ' K s ) (V.2) The levels of significance for V, and V 2 are discussed in section V 1.3. However, the s t a t i s t i c a l arguments presented there do not take into account the possible effects of interference or other unpredictable events. Because V 2 i s derived from a single observation of the source, i t i s p a r t i c u l a r l y susceptible to these e f f e c t s . Therefore, in a l l cases where either V, or V 2 indicate s i g n i f i c a n t v a r i a b i l i t y , the traces from the scans through the source are examined v i s u a l l y to ensure the quality of the data in each of the two receiver outputs. 111 1.2 Instrumental V a r i a t i o n s The amplitude of the s i g n a l produced by a r a d i o source at the r e c e i v e r outputs i s determined by three instrumental parameters; the r e c e i v e r gains, the antenna g a i n , and the antenna p o i n t i n g . V a r i a t i o n s i n these parameters produce s i g n a l v a r i a t i o n s that are p r o p o r t i o n a l to the s t r e n g t h of the s i g n a l . In t h i s s e c t i o n , the magnitude of these e f f e c t s i s d i s c u s s e d . In s e c t i o n V 1.3, these e f f e c t s are combined with the e f f e c t s of r e c e i v e r noise to y i e l d the t o t a l expected rms v a r i a t i o n as a f u n c t i o n of s i g n a l s t r e n g t h . The r e c e i v e r gains are c a l i b r a t e d every f i v e minutes d u r i n g the o b s e r v a t i o n s by f i r i n g a s t a b l e noise tube connected to the inputs of the r e c e i v e r s (see s e c t i o n II 2.1). The r e s u l t of each c a l i b r a t i o n i s applied- to a l l data obtained p r i o r to the next c a l i b r a t i o n (approximately f i v e minutes l a t e r ) , to convert the r e c e i v e r output to e q u i v a l e n t antenna temperature. The amplitude, of the r e c e i v e r response to the noise tube, shows a smooth v a r i a t i o n on a time s c a l e of hours with a range of, t y p i c a l l y , 10%-20%. Receiver gain v a r i a t i o n s on a time s c a l e of f i v e minutes, or l e s s , have an rms value of approximately 0.5%, which i s n e g l i g i b l e compared to other ef f e c t s . V a r i a t i o n s i n the antenna gain and p o i n t i n g can a r i s e from thermal expansion e f f e c t s on the s u p e r s t r u c t u r e of the t e l e s c o p e . The survey observing s e s s i o n s are scheduled in August so that the m a j o r i t y of the o b s e r v a t i o n s are c a r r i e d out at n i g h t , thereby a v o i d i n g l a r g e temperature g r a d i e n t s due to 1 1 2 f l u c t u a t i n g s o l a r i l l u m i n a t i o n . P o i n t i n g v a r i a t i o n s along the scan t r a c k have an rms value of about 13", but, because of the method used to measure source v a r i a t i o n s , these have no e f f e c t . The d i r e c t i o n p e r p e n d i c u l a r to the scan c o i n c i d e s with the f i x e d a x i s of the t e l e s c o p e , t h e r e f o r e p o i n t i n g v a r i a t i o n s i n t h i s d i r e c t i o n may be expected to be somewhat l e s s than along the scan. However, such changes w i l l produce v a r i a t i o n s i n the amplitude of the beam peaks p r o p o r t i o n a l to the slope of the beam gains at the o f f s e t of a source. U n f o r t u n a t e l y , i t i s not p o s s i b l e to d i s t i n g u i s h between the e f f e c t s of these p o i n t i n g changes and v a r i a t i o n s i n the antenna g a i n . The combined e f f e c t s are measured during the o b s e r v a t i o n s by i n c l u d i n g survey type scans through known f l u x s t a b l e c a l i b r a t i o n sources in a l l scan sequences. The data i n these scans are processed in the same manner as the survey data, to measure the " v a r i a b i l i t y " of the c a l i b r a t i o n sources. The r e s u l t s of t h i s a n a l y s i s f o r each year are shown i n t a b l e V, which l i s t s the measured one sigma v a r i a t i o n in the s i g n a l s t r e n g t h s over the e n t i r e observing s e s s i o n . The mean v a r i a t i o n remains constant at about 2% f o r a l l observing s e s s i o n s . No c o r r e l a t i o n was found among measurements obtained from d i f f e r e n t sources on the same n i g h t , i n d i c a t i n g that the antenna gain and p o i n t i n g v a r i a t i o n s occur on a time s c a l e l e s s than, or equal t o, a few hours. Although the rms value i s a good measure of the t y p i c a l amplitude of the instrumental v a r i a t i o n s , i t prov i d e s only l i m i t e d i n f o r m a t i o n about the range of the v a r i a t i o n s , i f the Table V. Instrumental Variations 1 977 Source «(%) 1978 Source *(%) 1979 Source *(%) 3C 48 2.3 DR 21 0.9 NGC 7027 3'. 6 3CR 27 1.5 3C 48 0.9 3C 52 1.5 3C 131 2.7 3C 142.1 2.8 3C 165 2.4 OV+080 2.1 NGC 7027 1.8 3CR 27 2.0 3C 52 1.5 3C 131 2.1 3C 142.1 3.3 3C 165 2.9 OV+080 3.1 NGC 7027 1.7 Mean rms = 2.27 Mean rms = 1.96 Mean rms = 2.37 1 14 IO CO < I977 J I l I I ' • 20h co < I Oh 1978 -I I L. J24 J L 1979 2 0 h CO < l O h _l L j I L -8 Figure 34. The amplitude d i s t r i bu t i on of instrumental var iat ions. The so l i d curves are gaussian that are normalized to the number of measurements, and have standard deviation equal to the mean rms var iat ion in each year. 1 1 5 amplitude d i s t r i b u t i o n d i f f e r s s i g n i f i c a n t l y from a normal, gaussian e r r o r d i s t r i b u t i o n . The amplitude d i s t r i b u t i o n s f o r each year are shown in f i g u r e 34. The s o l i d curves are gaussian, with standard d e v i a t i o n equal to the mean rms f o r that year, and normalized to the t o t a l number of o b s e r v a t i o n s . The curves and histograms do not d i f f e r s i g n i f i c a n t l y . T h e r e f o r e , the instrumental v a r i a t i o n s may be t r e a t e d as a n o i s e - l i k e phenomenon. 1.3 Monte C a r l o S i m u l a t i o n s The l e v e l of s i g n a l v a r i a t i o n caused by r e c e i v e r noise was measured v i a the second Monte C a r l o s i m u l a t i o n which i s d e s c r i b e d i n d e t a i l i n s e c t i o n IV.4. A r t i f i c i a l source p r o f i l e s of constant s t r e n g t h were i n s e r t e d i n t o the i n d i v i d u a l scans before c o n s t r u c t i n g the average, and the data were run through the source search and v a r i a b i l i t y measurement r o u t i n e s . Because the c o n f u s i o n s i g n a l does not vary from day to day, the measurement of short—term v a r i a t i o n s among the i n s e r t e d p r o f i l e s i s s u b j e c t to the e f f e c t s of r e c e i v e r noise alone. T h e r e f o r e , the expected rms f r a c t i o n a l source v a r i a t i o n should conform to a r e l a t i o n s h i p of the form of equation V.3. f e=n-* n/D p p (V.3) Here <rn i s the noise l e v e l i n a s i n g l e o b s e r v a t i o n ( s i n g l e scan), Dp p i s the peak to peak s i g n a l d e f l e c t i o n of the average source p r o f i l e , and n i s a constant f a c t o r which depends upon the method of measurement. An e m p i r i c a l value f o r n was determined by f i t t i n g 1 16 equation V.3 to the Monte C a r l o r e s u l t s from the i n s e r t s i n t o the 1977 data base. Only 1977 was used f o r t h i s purpose because the l a r g e number of o b s e r v a t i o n s per source i n that year (^20) ensures that f v i s adequately d e f i n e d . F i g u r e 35 shows the observed f r a c t i o n a l source v a r i a t i o n as a f u n c t i o n of Dpp/<rn f o r these i n s e r t s . The r e s u l t s are f i t t e d w e l l by equation V.3 with n = 2.1, which i s shown by the s o l i d l i n e . The dashed l i n e i n the f i g u r e , c orresponding to v a r i a t i o n s of twice f e (V 1=2), i s i n c l u d e d f o r r e f e r e n c e . In f i g u r e 36, the r e s u l t s of the Monte C a r l o s i m u l a t i o n are shown combined with the rms gain v a r i a t i o n s to y i e l d the t o t a l expected rms source v a r i a t i o n as a f u n c t i o n of D p p . The curves are d e r i v e d from equation V.4 with < j g = .022 and n = 2.1. V = "g + (i-«n/Dpp>2 • <v-4> At the low s i g n a l end, two curves are shown. The upper, dashed curve corresponds to o b s e r v a t i o n s with one r e c e i v e r only (1979). The lower, s o l i d l i n e r e presents the r e s u l t s of combining the r e c e i v e r output. Estimates of the l e v e l s of s i g n i f i c a n c e f o r the v a r i a b i l i t y i n d i c e s are obtained from the d i s t r i b u t i o n of V, and V 2 among the Monte C a r l o source i n s e r t s . For n o n — v a r i a b l e s sources, the index V:, by d e f i n i t i o n , has an e x p e c t a t i o n value of one. D e v i a t i o n s from t h i s value a r i s e from two e f f e c t s ; the s t a t i s t i c a l underestimation of * v f o r i n s e r t s f o r which few "o b s e r v a t i o n s " are a v a i l a b l e , and random noise i n the measurement of both * v and the peak to peak d e f l e c t i o n , D p p, from which f i s c a l c u l a t e d . For sources l o c a t e d i n scan 1 17 ] 1 1 i i i i i i j 1 1 1 1 — i — i — r - r \ \ J ' ' 1 — » » i i I 1 I I I • • • ' I _t 10 100 Dpp/a-n Figure 35. The f ract iona l rms signal var ia t ion due to receiver noise, as a function of peak to peak signal to noise r a t i o . The dots are the results of a r t i f i c i a l source inserts in the 1977 data base. The open c i r c l e s are a sample of the inserts into 1979 data. Equation V.3, with 7?=2.1, i s shown by the s o l i d l i n e . The dashed l i ne i s twice f . 118 T 1 1 1—I I I I j T 1 1 1 1 I I 0.1 \ 10 100 1000 (mk) Figure 36. The expected f ract iona l rms signal var iat ion as a function of peak to peak def lec t ion . The s o l i d l i n e i s for combined receiver outputs, and the dashed l i n e i s fo r observations with a s ingle receiver. 1 19 sequences that are repeated only two or three times, the underestimation of <rv i s s u b s t a n t i a l (^50%). In these cases, V, i s not an e f f e c t i v e measure of the s i g n i f i c a n c e of the observed v a r i a t i o n s . The second v a r i a b i l i t y index, V 2, which i s independent of the number of o b s e r v a t i o n s , i s the best i n d i c a t o r of v a r i a b i l i t y f o r these sources. T h e r e f o r e , i n determining the l e v e l s of s i g n i f i c a n c e f o r V,, only i n s e r t s i n t o scans f o r which the number of o b s e r v a t i o n s i s g r e a t e r than 5 have been used. F i g u r e 37 shows, for each index, the f r a c t i o n of i n s e r t s with value exceeding V, or V 2, as a f u n c t i o n of V, and V 2. The t y p i c a l number of o b s e r v a t i o n s per source, f o r V,, of about 6, r e s u l t s i n a mean value of Vi of 0.8. For p u r e l y random n o i s e , the histograms i n f i g u r e 37 have the form of an i n t e g r a l gaussian d i s t r i b u t i o n , given by 1 - e r f ( x ) . The t a i l of such a d i s t r i b u t i o n i s , i t s e l f , w e l l represented by a normal e r r o r curve. T h e r e f o r e , to determine the p r o b a b i l i t y of l a r g e d e v i a t i o n s , normal e r r o r curves have been f i t t e d to the t a i l s of both d i s t r i b u t i o n s . The agreement between the histograms and the curves i s q u i t e good. Sources are c l a s s e d as v a r i a b l e i f the p r o b a b i l i t y of occurence of the measured values of V, or V 2 i s l e s s than 0.1%. From the normal e r r o r curves, an upper l i m i t of 0.1% corresponds to V,>1.85 and/or V 2>3.5. Sources f o r which the p r o b a b i l i t y of V, or V 2 i s l e s s than 1% , corresponding to V,>1.6 and/or V 2>2.9, but g r e a t e r than 0.1%, are c l a s s e d as p o s s i b l e v a r i a b l e s . 1 2 0 Figure 37 . The d i s t r i b u t i o n of short-term v a r i a b i l i t y i n d i c e s w i t h value greater than V. (top) and V (bottom) f o r the a r t i f i c i a l source i n s e r t s . The data have been coverted to p r o b a b i l i t i e s by n o r m a l i z i n g to the t o t a l number of i n s e r t s . S o l i d curves are normal e r r o r curves f i t t e d to the t a i l s of the d i s t r i b u t i o n s . 121 2. Long—term V a r i a t i o n s 2.1 Method Y e a r l y v a r i a t i o n s are measured by comparing source s t r e n g t h s between two observing s e s s i o n s . Because of d i f f e r e n c e s i n the t e l e s c o p e p o i n t i n g from year to year the o f f s e t of a source changes from one observing s e s s i o n to another. T h e r e f o r e , the comparison i s based on the source s t r e n g t h , ( K s ) , which i s normalized to the beam peaks and takes i n t o account the r e l a t i v e s t r e n g t h s of the beams at the o f f s e t of the source. The f i n a l t e l e s c o p e gain c a l i b r a t i o n s are not a p p l i e d , s i n c e absolute f l u x d e n s i t i e s are not r e q u i r e d f o r t h i s purpose, and the u n c e r t a i n t i e s i n the gains would introduce unnecessary noise i n t o the comparison. Instead, the systematic d i f f e r e n c e s i n the gain between 'observing s e s s i o n s i s measured d i r e c t l y using the sample of survey sources found to have constant f l u x d e n s i t y . Flux s t a b l e sources are d i s t i n g u i s h e d from p o s s i b l e y e a r l y v a r i a b l e s using an i t e r a t i v e procedure based on f i t t i n g a smooth curve to the d e c l i n a t i o n dependence of a measure of the f r a c t i o n a l d i f f e r e n c e i n source s t r e n g t h s between two observing s e s s i o n s . The comparison i s r e s t r i c t e d to sources that are unresolved by the telesope beam to a v o i d source s o l i d angle e f f e c t s . For each unresolved source d e t e c t e d i n at l e a s t two of the three observing s e s s i o n s having s t r e n g t h K, i n the f i r s t year and K 2 i n the second, the q u a n t i t y I given by equation V.5 i s c a l c u l a t e d , along with an e r r o r € based on the i n d i v i d u a l e r r o r s on the source s t r e n g t h s . 1 22 I = 2-[(Kj-K,)/(K 2+K,)] (V.5) The f a c t o r of 2 i s i n c l u d e d so that I corresponds to the f r a c t i o n a l v a r i a t i o n i n the mean source s t r e n g t h . The systematic gain d i f f e r e n c e between the two observing s e s s i o n s produces an i n t r i n s i c value of I, denoted by I 0 , that i s a f u n c t i o n of d e c l i n a t i o n . For the purpose of d e f i n i n g I 0 ( 6 ) , a sample of the survey sources are used f o r which the e r r o r , e, i s l e s s than some l i m i t ec . The value of € cadopted was based on a compromise between the degree of accuracy on the i n d i v i d u a l values of Ij and the s i z e of the sample of sources used. For 1978 to 1979 ec was set to .05. However, f o r 77-78 and 77-79 fewer sources are a v a i l a b l e , and e cwas i n c r e a s e d to 0.1 to provide an adequate data base. Sources with o f f s e t from the c e n t r a l scan t r a c k that i s g r e a t e r than 1.5 arc-minutes were not used i n c o n s t r u c t i n g I 0 ( 6 ) . An i n i t i a l approximation to I 0 ( 6 ) i s obtained by f i t t i n g a f o u r t h order polynomial to the d e c l i n a t i o n dependence of the va l u e s Ij . The rms s c a t t e r («r0) of .the data about the f i t i s c a l c u l a t e d . T h i s s c a t t e r about the smooth curve i s composed of two components; one due to the u n c e r t a i n t i e s i n the Ij , which can be represented by a normal e r r o r d i s t r i b u t i o n , and the other a r i s i n g from v a r i a t i o n s i n source s t r e n g t h s between the two observing s e s s s i o n s . To ensure that only f l u x s t a b l e sources are used to d e f i n e I 0 ( 6 ) , a l l sources f o r which A j = 11 o (<5 )-I j | i s g r e a t e r than 2e0 are r e j e c t e d from the data base. A new I 0 ( 6 ) i s c a l c u l a t e d and the process i t e r a t e d u n t i l no r e j e c t i o n s occur; that i s , a l l Ij are w i t h i n 2a0 of I 0 . 123 With a r e j e c t i o n l i m i t of 2<s0 approximately 95% of the f l u x s t a b l e sources are used i n determining I 0 ( 6 ) . A higher r e j e c t i o n l i m i t , i n the presence of a non-normal d i s t r i b u t i o n with a s i g n i f i c a n t number of A j i n the region of the t a i l of the normal component, leads to a l a r g e o v e r e s t i m a t i o n of a 0 . A histogram of the d e v i a t i o n , A j , f o r a l l sources i n c l u d e d in the f i r s t i t e r a t i o n of the 1978-1979 f i t to I 0 ( 6 ) i s shown in f i g u r e 38. The s o l i d curve i s the expected normal e r r o r d i s t r i b u t i o n based on the measured a0 of .078 and normalized to the number of sources i n c l u d e d in the f i n a l i t e r a t i o n . The agreement between the gaussian and the c e n t r a l peak of the d i s t r i b u t i o n i s q u i t e good. Furthermore, the rms of .078 i s i n good agreement with the combined e r r o r of about .05 on the values Ij and .02-.05 on I 0 ( 6 ) . The three curves I 0 ( 6 ) , f o r the comparisons between the observing s e s s i o n s , are shown in f i g u r e 39. To give a rough i n d i c a t i o n of the u n c e r t a i n t i e s i n the r e s u l t s , the mean values of I j , i n bins of f i v e degrees, and the e r r o r s on the means are a l s o p l o t t e d . T y p i c a l e r r o r s range from about .02 at high d e c l i n a t i o n s , where a l a r g e number of sources are a v a i l a b l e , to about .05 at lower d e c l i n a t i o n s . E r r o r s are s l i g h t l y l a r g e r for comparisons to 1977 because of the smaller number of sources in the data base. Long—term v a r i a t i o n s among the survey sources are detected by comparing the value of Ij , for a l l sources d e t e c t e d i n two observing s e s s i o n s , to I 0 ( 6 )• For a s p e c i f i c value of e j , the d i s t r i b u t i o n of A j f o r n o n — v a r i a b l e sources has standard - 6 0 - 4 0 - 2 0 0 I - I o 2 0 4 0 6 0 Figure 38. The d i s t r ibut ion of deviations from the mean f ract ion dif ference in source strength, I0. between 1978 and 1979. The histogram includes a l l sources used in the f i r s t i t e r a t i on to calculate I 0. The so l i d curve i s a gaussian, normalized to the number of sources in the f i na l i t e r a t i o n , with standard deviation equal to the rms scatter about the mean. CO 125 30 20 To l0> L 1978-1979 -10 -10 -20 CO -30 10 S 0 -10 J I L I 1977-1978 J L Ll I I L L 1977-1979 J L J L 10 20 30 40 50 60 70 Decl inat ion (°) Figure 39. The i n t r i n s i c long-term f rac t i ona l s ignal v a r i a t i on , I Q ( 6 ) , between each pa i r of observing sessions. The value of I 0, and the one sigma 5° dec l inat ion bins. crosses show error on .the the mean mean, i n i 1 1 r 1 2 3 4 5 6 7 Figure 40. The d i s t r i bu t i on of long-term v a r i a b i l i t y indices for a l l sources detected in both 1978 and 1979. The curve is a normalized gaussian with a standard deviation of one. to 1 27 d e v i a t i o n <s^= \Jco+e?. A source i s c l a s s e d as v a r i a b l e i f the p r o b a b i l i t y of Aj i s l e s s than about 0.1%, or, a l t e r n a t e l y , i f Aj/^> 3.5. Sources with 3.0 <Aj/<^<3.5 are c l a s s e d as p o s s i b l e v a r i a b l e s . F i g u r e 40 shows the d i s t r i b u t i o n of A/<^ f o r a l l sources d e t e c t e d i n both the 1978 and 1979 o b s e r v i n g s e s s i o n s . The s o l i d curve i s a gaussian with a standard d e v i a t i o n of one. As f o r short—term v a r i a b i l i t y , i n a l l cases where v a r i a b i l i t y i s i n d i c a t e d , the raw scan t r a c e s are examined to ensure the q u a l i t y of the data. T h i s a n a l y s i s i s , of course, r e s t r i c t e d to sources d e t e c t e d d u r i n g two observing s e s s i o n s . Because of the l o g i s t i c s of the o b s e r v a t i o n s (see Table I I ) , the r e c e i v e r n o i s e power in the average scan of a p a r t i c u l a r sequence i s much l a r g e r in one observing s e s s i o n than the other. Thus, in order f o r a source to be d e t e c t e d i n more than one year, i t must be strong enough to be d e t e c t a b l e i n an average scan comprised of as few as one o b s e r v a t i o n . Consequently, fo r many of the weaker sources, v a r i a b i l i t y on the long term cannot be determined. Furthermore, some stronger sources with l a r g e o f f s e t may be d e t e c t e d i n only one year because the change in the p o i n t i n g e r r o r s of the t e l e s c o p e p l a c e s the source o u t s i d e of the range of a scan for one of the observing s e s s i o n s . On the other hand, the p o s s i b i l i t y e x i s t s that a source w i l l be d e t e c t e d i n only one s e s s i o n because of v a r i a b i l i t y . To check for t h i s phenomenon, the computer r o u t i n e that c a r r i e s out the comparison of s t r e n g t h s between s e s s i o n s i s programmed to f l a g sources with no c o u n t e r p a r t but with s u f f i c i e n t s t r e n g t h , i n 1 28 the year d e t e c t e d , to have produced a peak to peak s i g n a l to noise r a t i o of g r e a t e r than twenty i n the other s e s s i o n s (see f i g u r e 27 f o r d e t e c t i o n p r o b a b i l i t y versus s i g n a l to n o i s e ) . 2.2 L i m i t a t i o n s Aside from the obvious r e s t r i c t i o n of measurable long—term v a r i a t i o n s to sources d e t e c t e d i n more than one observing s e s s i o n , the u n c e r t a i n t i e s on I 0 ( 6 ) , and on the i n d i v i d u a l values of the source s t r e n g t h , impose lower l i m i t s on d e t e c t a b l e v a r i a t i o n s . The u n c e r t a i n t y i n the source s t r e n g t h from one observing s e s s i o n can be a t t r i b u t e d to three e f f e c t s ; r e c e i v e r n o i s e , u n c e r t a i n t y in the beam model and instrumental v a r i a t i o n s . For the purpose of e s t i m a t i n g the e f f e c t s on the long term v a r i a b i l i t y index, i t i s convenient to parameterize the e r r o r on the s t r e n g t h , K, i n the form a^= a+b«K. The c o e f f i c i e n t a i s determined by the r e c e i v e r noise l e v e l . Although the e f f e c t s of r e c e i v e r noise has an o f f s e t dependence (see equation IV.8), to f i r s t order, t h i s dependence can be ignored and the c o e f f i c i e n t a set to 3 mK, which i s equal to \J~2 times the t y p i c a l noise l e v e l in an average scan. The f a c t o r of y/2 i s obtained by t a k i n g the two terms in equation IV.8 to be of about equal magnitude. The c o e f f i c i e n t b i s given by the combined e f f e c t s of u n c e r t a i n t i e s i n the beam model (<2%) and i n s t r u m e n t a l v a r i a t i o n s (2.2%). Instrumental v a r i a t i o n s w i l l average out i f s e v e r a l o b s e r v a t i o n s are o b t a i n e d . However, f o r most sources, d u r i n g one of the observing s e s s i o n s , only one or 129 two o b s e r v a t i o n s were c a r r i e d out. Ther e f o r e , the c o e f f i c i e n t b i s set to 3%. D e f i n i n g an average source s t r e n g t h between obs e r v i n g s e s s i o n s , K=(K 1+K 2)/2, the e r r o r on the q u a n t i t y I (equation V.5) i s , approximately, e=tf k/K. Thus f o r an average e r r o r on I 0 of .03, the e r r o r on A as a f u n c t i o n of K i s given by: <s*= 0.00l8+(0. l8/K) + (9/R) 2 (V.6) For l a r g e values of K, the l a s t two terms v a n i s h , and the v a r i a b i l i t y d e t e c t i o n l i m i t of 3.5«e^ i s e q u i v a l e n t to A ^ 0.15, which corresponds to a change in the source s t r e n g t h between observing s e s s i o n s of 16%. This l i m i t i n c r e a s e s to about 50% f o r K=100 mK and 100% f o r K=50 mK, which f o r the median s e n s i t i v i t y of 0.67 K/Jy correspond to f l u x d e n s i t i e s of 150 and 75 mJy, r e s p e c t i v e l y . 130 CHAPTER VI THE CATALOGUE OF COMPACT RADIO SOURCES 1. I n t r o d u c t i o n The search of the f i r s t f i v e sequences of survey o b s e r v a t i o n s , which comprise about 40% of the t o t a l survey of the northern g a l a c t i c plane, r e s u l t e d i n the d e t e c t i o n of 806 compact sources of r a d i o emission. With the exception of a few sources f o r which only one o b s e r v a t i o n was obtained, each source has been examined f o r v a r i a b i l i t y on a time s c a l e of days, and f o r many of the sources, long-term (~one year) v a r i a b i l i t y i n f o r m a t i o n has been obtained. T h i s chapter p r e s e n t s the r e s u l t s in the form of a catalogue of compact sources. It i s a p p r o p r i a t e , at t h i s p o i n t to b r i e f l y r e s t a t e the ba s i c p r o p e r t i e s of the survey. A compact r a d i o source i s d e f i n e d as a region e x h i b i t i n g a s i g n i f i c a n t excess of emission above the background l e v e l , with the s i g n a t u r e of an in s t r u m e n t a l p r o f i l e . The weakest a c c e p t a b l e excess i s l i m i t e d by the e x t r a g a l a c t i c c o n f u s i o n l e v e l to a minimum f l u x d e n s i t y of 10 mJy. Where r e c e i v e r noise i s the l i m i t i n g f a c t o r , the minimum ranges up to 17 mJy. In a d d i t i o n , each d e t e c t i o n must be e i t h e r i s o l a t e d from regions of strong g a l a c t i c c o n f u s i o n s t r u c t u r e , or stand out s t r o n g l y , on v i s u a l examination of the scan t r a c e s , above such s t r u c t u r e . As a r e s u l t of the v a r i a t i o n in the g a l a c t i c c o n f u s i o n l e v e l with p o s i t i o n i n the g a l a c t i c plane, the inhomogeneity of 131 the noise p r o p e r t i e s between the scan sequences, and the change i n the t e l e s c o p e s e n s i t i v i t y with d e c l i n a t i o n ; the search of the data f o r compact sources i s not uniform i n s e n s i t i v i t y . The cataloque i n c l u d e s sources down to a minimum f l u x d e n s i t y of 10 mJy, from scans with the lowest noise l e v e l . However, the average s e n s i t i v i t y of the survey i s more t y p i c a l l y 20-30 mJy, and, i n r e s t r i c t e d r e g i o ns of very s t r o n g g a l a c t i c c o n f u s i o n , the minimum d e t e c t a b l e f l u x d e n s i t y may be as high as a few Jansky. In p r a c t i c e g a l a c t i c c o n f u s i o n i s a s e r i o u s problem i n only a small p o r t i o n (~13%) of the survey area, p r i m a r i l y i n the l o n g i t u d e i n t e r v a l s 40°<1<55°, 78°<1<86° and 111°<1<114°. The beam—switching observing technique, combined with the f i g u r e of merit t e s t c r i t e r i o n , l i m i t s source d e t e c t i o n s to emission regions with angular extent i n the d i r e c t i o n of the scan of l e s s than about 6 arc-minutes. Below t h i s l i m i t an attempt has been made to measure angular diameters by f i t t i n g gaussians to the observed source p r o f i l e s . For strong sources t h i s technique provides angular diameters a c c u r a t e to about h a l f an arc-minute. However, f o r weaker sources (a few 10's of mJy), a true p o i n t source i s i n d i s t i n g u i s h a b l e from a source with 1-2 arc-minute extent, and measured diameters are only s u f f i c i e n t l y a c c u r a t e to i n d i c a t e whether the source has d e t e c t a b l e extent beyond t h i s . In the d i r e c t i o n p e r p e n d i c u l a r to the scan, sources with angular extent g r e a t e r than about 5 arc-minutes at high d e c l i n a t i o n s , and 10 arc-minutes at low d e c l i n a t i o n s , produce c o r r e l a t e d p r o f i l e s i n three or more 1 32 adjacent scans and are d i s c a r d e d i f no v a r i a b l e component i s e v i d e n t . Short—term v a r i a b i l t y i s assessed on the b a s i s of a minimum of two, to a maximum of twenty, f l u x d e n s i t y measurements obtained d u r i n g one observing s e s s i o n , with a sample i n t e r v a l ranging from one to 17 days. More t y p i c a l l y f i v e or s i x o b s e r v a t i o n s per source are obtained, with a minimum s e p a r a t i o n of one or two days. The minimum d e t e c t a b l e v a r i a t i o n i s l i m i t e d by i n s t r u m e n t a l v a r i a t i o n s to a l e v e l of about 10% f o r strong sources. At low f l u x d e n s i t i e s r e c e i v e r noise l i m i t s the d e t e c t i o n of v a r i a t i o n s to a peak to peak amplitude of 40 mK. V a r i a t i o n s on the long—term are measured by comparison of source s t r e n g t h s between two observing s e s s i o n s . Because scan sequences are repeated a number of times d u r i n g one observing s e s s i o n and only a few times in the other, the r e c e i v e r noise l e v e l i s much higher i n one year. Consequently, long term v a r i a b i l i t y i n f o r m a t i o n i s a v a i l a b l e only f o r strong sources, and those weaker sources which have small o f f s e t from the c e n t r a l scan t r a c k . E r r o r s on the i n d i v i d u a l source s t r e n g t h s l i m i t measurable v a r i a t i o n s f o r strong sources to g r e a t e r than 16%. T h i s l i m i t r a p i d l y i n c r e a s e s as f l u x d e n s i t y decreases. V a r i a t i o n s of 100% are undetectable f o r mean f l u x d e n s i t i e s below 75 mJy. 133 2. The Catalogue The catalogue of compact r a d i o sources i s presented i n Table VI. Column 1 l i s t s the source name. F o l l o w i n g the recommendation of Commission 28 of the I n t e r n a t i o n a l Astronomical Union, i n order to provide u n i f o r m i t y i n the nomenclature of as t r o n o m i c a l o b j e c t s and to f a c i l i t a t e comparisons between c a t a l o g u e s , the e i g h t d i g i t 'Parkes' system has been used to designate the sources. The f i r s t four d i g i t s g i ve the hours and minutes of r i g h t ascension of the source co-o r d i n a t e s , and the l a s t four give the sign and degrees of d e c l i n a t i o n truncated to a tenth of a degree. Columns 2 and 3 give the c o - o r d i n a t e s of the source i n epoch 1950 r i g h t a scension and d e c l i n a t i o n . The quoted u n c e r t a i n t y i s the one sigma e r r o r based on the combined u n c e r t a i n t i e s i n the observed c o - o r d i n a t e s and the p o i n t i n g c o r r e c t i o n . For sources detected in more than one observing s e s s i o n the c o - o r d i n a t e s with the l e a s t e r r o r (due to a higher s i g n a l to noise d e t e c t i o n and/or b e t t e r c a l i b r a t i o n ) are adopted. The new g a l a c t i c l o n g i t u d e and l a t i t u d e of the source, to w i t h i n a tenth of a degree, are given in columns 4 and 5. The mean f l u x d e n s i t y and the estimated one sigma e r r o r are l i s t e d i n column 6. As f o r the source c o - o r d i n a t e s , the value of the f l u x d e n s i t y given r e p r e s e n t s the ob s e r v a t i o n y i e l d i n g the l e a s t e r r o r . In column 7, an estimate of the angular extent of the source i s given. A numerical entry in t h i s column i s the angular diameter, to the nearest minute of a r c , i n the d i r e c t i o n of the scan through the source. Sources with p r o f i l e s c o n s i s t e n t with an unresolved 134 source are designated 'P', and sources with p r o f i l e s that e x h i b i t s i g n i f i c a n t beam broadening, but provide i n s u f f i c e n t s i g n a l to noise to allow an accurate d e t e r m i n a t i o n of the angular diameter, are l a b e l l e d 'E'. Columns 8 to 13 present the r e s u l t s of the search f o r v a r i a b i l i t y among the source d e t e c t i o n s . Column 8 g i v e s the number of o b s e r v a t i o n s used to c a l c u l a t e d the short—term v a r i a b i l i t y i n d i c e s V, and V 2, given i n columns 9 and 10. For sources d e t e c t e d during more than one observing s e s s i o n , these e n t r i e s are taken e i t h e r from the s e s s i o n y i e l d i n g the maximum number of o b s e r v a t i o n s or, i n the case of a v a r i a b l e source, the s e s s i o n showing the best evidence f o r v a r i a b i l i t y . Column 11 presents an assessment of the v a r i a b i l i t y e x h i b i t e d by the source, based on the short—term i n d i c e s . An 'N' i n d i c a t e s that no evidence f o r short—term v a r i a t i o n s i s found, and a 'P' denotes a p o s s i b l e v a r i a b l e . Sources with a 'Y' i n t h i s column show c l e a r evidence of short term v a r i a b i l i t y . For sources with f l u x d e n s i t y measurements a v a i l a b l e from more than one observing s e s s i o n , the long term v a r i a b i l i t y index i s l i s t e d i n column 12. In column 13, an assessment of the observed long—term v a r i a b i l i t y i s presented using the same scheme as f o r the short term measurements. Some of the survey sources, p a r t i c u l a r l y the stronger ones, are l i s t e d i n e a r l i e r c a t a l o g u e s of r a d i o sources. Dixon (1970) has compiled a master l i s t of e n t r i e s i n r a d i o source catalogues that i s f r e q u e n t l y updated. The survey sources were checked a g a i n s t the 1976 v e r s i o n of t h i s l i s t . When an 1 35 i d e n t i f i c a t i o n has been made, column 14 g i v e s the a l t e r n a t e source d e s i g n a t i o n . Most of these e a r l i e r surveys were c a r r i e d out at low f r e q u e n c i e s ( t y p i c a l l y a few hundred MHz), with r e s o l u t i o n of 10's of minutes of arc and s e n s i t i v i t y of the order of a Jansky. An index to the r a d i o source c a t a l o g u e s , i n c l u d i n g a b r i e f d e s c r i p t i o n of the surveys and r e f e r e n c e s to the l e t t e r coded p r e f i x i n the source names, i s provided by Kesteven and B r i d l e (1977). T a b l e V I . A CATALOGUE OF COMPACT RADIO SOURCES NAME RA(1950) h m s DEC(1950) 1 b F l u x D e n s i t y (mJy) D1am No. S h o r t V. V a r l a t I o n s Term V, VAR? Long Index Terra VAR? Other C a t a l o g u e s GTOOO1+625 O 1 0 + 8 62 31 29 ± 43 117 5 0 4 20O ± 23 1 14 0 70 1 .44 N 0.78 N BG 0001+62 GT0001+631 o 1 1 + 8 63 9 12 ± 78 1 17 6 1 1 42 ± 10 E 2 0 06 0.13 N 0.0 -GT0001+613 0 1 46 + 3 61 21 7 + 58 1 17 4 -0 7 50 ± 8 P 14 0 98 1 .85 N 1.70 N GT0002+609 0 2 6 + 1 60 58 43 ± 53 1 17 3 -1 1 76 ± 10 P 6 0 74 1 .09 N 1 .67 N GT0002+634 0 2 53 + 4 63 24 35 ±103 1 17 9 1 3 40 + 1 1 P 6 0 75 1 .33 N 1.41 N GTCO03+637 0 3 30 + 2 63 43 33 ± 91 1 18 0 1 6 32 ± 4 E 6 0 64 0.99 N 0.0 -GT0O04+629 0 4 52 + 1 62 56 28 ± 43 1 18 0 0 8 57 ± 7 P 4 0 93 1 .46 N 0.0 -GT0004+615 0 4 56 + 3 61 32 22 ± 67 1 17 8 -0 6 26 ± 7 P 2 1 14 1 .28 N 0.0 -GT0O05+626 0 5 20 + 2 62 39 23 + 47 1 18 0 0 5 84 ± 10 P 6 0 58 1 . 19 N 0.47 N GT0005+601 0 5 38 + 5 60 8 0 ± 80 1 17 6 -2 0 51 ± 10 P 6 0 92 1 .72 N 1 .05 N GT0006+617 0 6 43 + 2 61 43 49 + 47 1 18 0 -0 5 25 ± 4 E 6 0 69 1 . 18 N O.O -GT0007+602 0 7 17 + 2 60 13 41 ± 63 1 17 8 -2 0 27 ± 5 P 16 1 1 1 2.07 N 1 .48 N GTCO07+635 0 7 35 + 2 63 30 19 + 55 1 18 4 1 3 31 ± 4 P 6 0 78 1 .42 N 0.0 -GT0008+618 0 8 7 + 2 61 48 37 + 169 1 18 2 -0 4 36 ± 7 P 2 0 04 0.09 N 0.0 -GT0009+635 0 9 15 + 2 63 31 44 ± 78 1 18 6 1 3 28 ± 6 E 3 0 72 0.95 N 2.82 N GT0010+614 O 10 19 + 8 61 28 50 + 74 1 18 4 -0 8 36 ± 9 P 2 0 46 0.48 N 0.0 -GT0010+627 0 10 25 + 8 62 45 45 ± 83 1 18 6 0 5 39 ± 9 P 16 0 74 1 .25 N 1 .05 N GTOO12+605 0 12 3 + 2 60 35 45 ±198 118 5 -1 7 24 ± 5 P 16 0 78 1 .42 N 0.59 N GTOO12+641 0 12 21 + 2 64 9 38 ± 93 1 19 0 1 8 41 + 10 P 1 - - - 0.0 -GTO013+633 0 13 42 + 4 63 18 20 ± 79 1 19 0 1 0 40 ± 1 1 P 1 - - - O.O -GTOO15+614 0 15 50 + 5 61 27 43 ± 70 1 19 0 -0 9 63 ± 11 E 6 0 85 1 .70 N 0.07 N GTOO18+626 0 18 35 + 2 62 36 44 ±104 1 19 5 0 2 35 + 8 P 6 1 1 1 1 .90 N 0.0 N GTOO19+611 0 19 18 ± 1 61 8 39 ± 30 1 19 4 -1 3 51 ± 5 P 6 0 82 1 .40 N 0.0 -GT0019+603 0 19 55 + 1 60 23 36 ± 30 1 19 4 -2 0 124 ± 13 2 4 0 70 0.95 N 0.74 N GT0020+606 0 20 8 + 2 60 36 41 + 93 1 19 5 -1 8 35 ± 6 P 16 0 69 1 .37 N 2.58 N GT0021+627 0 21 21 + 5 62 44 29 ±123 1 19 8 0 3 24 ± 6 E 2 0 38 0.44 N 0.0 -GT0023+615 0 23 50 + 1 61 33 0 ± 74 120 0 -0 9 38 + 6 E 6 0 68 1 .37 N 0.0 -GT0024+611 0 24 51 + 2 61 8 6 ± 73 120 1 -1 3 25 + 4 E 6 0 55 0.79 N 0.0 , -GT0025+605 0 25 0 + 1 60 30 20 ± 43 120 0 -2 0 67 ± 8 2 16 0 75 1.51 N 2. 15 N GT0025+621 0 25 37 + 2 62 10 52 + 50 120 3 -0 3 64 ± 8 P 6 0 78 1 .40 N 0.34 N GT0025+638 0 25 52 + 2 63 51 55 ± 97 120 5 1 4 46 ± 8 P 6 0 37 0.75 N 0.90 N GT0026+619 0 26 9 + 8 61 59 38 ±130 120 3 -0 5 22 ± 7 E 16 0 66 1 .40 N 1 .27 N GTO026+627 0 26 30 + 2 62 46 58 ± 36 120 4 0 3 39 + 5 2 5 2 06 3.51 Y 0.02 N GTO026+637 0 26 55 + 1 63 42 24 + 25 120 6 1 2 957 ± 96 P 16 0 89 2 . 27 N 1 .85 N BG 0026+63 GT0027+634 0 27 17 + 2 63 25 34 ± 63 120 6 0 9 33 ± 4 P 6 0 59 0.75 N 0.0 -GT0027+629 0 27 32 + 2 62 56 28 + 44 120 6 0 4 26 ± 4 P 6 0 87 1 .63 N 0.0 -GT0028+604 0 28 44 + 3 60 28 16 ±123 120 5 -2 0 14 ± 3 E 6 0 47 0.70 N 0.0 -GT0028+631 0 28 45 + 8 63 6 5 ± 79 120 7 0 6 93 ± 23 1 15 0 97 2.05 N 1 .30 N GT0028+625 0 28 51 + 8 62 34 48 ±106 120 7 0 1 36 ± 9 P 15 o 84 1 .74 N 0.97 N GT0030+623 0 30 2 + 2 62 18 27 ± 70 120 8 -0 2 25 ± 4 P 6 0 70 1 .03 N O.O -GT0030+610 0 30 25 + 2 61 2 6 ±123 120 8 -1 5 28 ± 5 P 15 0 86 1 .40 N 1 .40 N GT0030+619 0 30 39 + 2 61 54 2 ± 72 120 8 -0 6 16 ± 3 P 15 0 72 1 .96 N 0.0 -GT0032+620 0 32 26 + 8 62 0 39 ± 75 121 1 -0 5 31 ± 9 P 6 0 92 1 .33 N 0.0 -Table V I . Continued NAME RA(1950) h m s DEC(1950) * / II 1 b Flux Density (m Jy) Diam No. Short V i VarlatIons Term V i VAR? Long Index Term VAR? Other Catalogues GT0032+612 0 32 31 + 1 61 14 12 + 30 121 .0 - 1 3 294 + 31 P. 6 0 63 1 . 28 N 1 18 N GT0033+604 0 33 32 + 2 60 28 42 ± 54 121 . 1 -2 1 27 + 6 P 2 1 12 1 . 18 N 0 0 -GT0034+623 0 34 15 + 1 62 19 46 + 24 121 .3 -0 2 437 • 44 P 6 0 73 1 .45 N 0 65 N BG 0034+62 GT0035+645 0 35 33 + 2 64 32 10 ± 94 121 6 2 0 51 + 1 1 P 1 - - - 0 0 -GT0038+615 0 38 51 + 5 61 31 17 ±125 121 8 -1 1 26 + 5 P 6 0 87 1 .90 N 0 0 -GT0039+622 o 39 18 + 2 62 12 34 ± 60 121 9 -0 4 30 + 6 E 6 1 14 2.13 N 1 02 N GT0O39+630 0 39 56 ± 7 63 5 23 + 97 122 0 0 5 30 + 7 P 6 0 64 1 .20 N 0 89 N GT0040+637 0 40 44 + 1 63 43 56 ±113 122 1 1 1 34 + 4 4 15 O 86 1 .64 N 0 0 -GT0041+619 0 41 15 + 2 61 59 1 1 ±150 122 1 -0 6 32 + 4 P 6 0 77 1 .33 N 0 0 -GT0042+610 0 42 13 + 4 61 1 21 ±124 122 2 - 1 6 51 + 12 P 6 0 79 1 .73 N 0 56 N GT0O43+621 0 43 47 + 2 62 9 26 ± 94 122 4 -0 4 21 + 4 P 6 0 95 1 .21 N 0 0 -GT0043+625 0 43 58 + 2 62 30 15 ± 55 122 4 -0 1 51 + 7 P 6 1 27 1 .90 N 0 95 N GT0044+642 0 44 45 + 2 64 15 57 ±108 122 5 1 7 28 + 5 E 6 0 83 1 .58 N 0 0 -GT0045+621 0 45 48 + 1 62 8 2 ± 71 122 6 -0 5 86 + 13 P 6 0 90 1 .46 N 0 48 N GTCX>45+643 0 45 56 + 5 64 22 29 ± 35 122 7 1 8 87 + 1 1 P- 6 1 82 3.50 Y 2 64 N GT0046+606 0 46 53 + 2 60 37 40 ± 47 122 7 -2 0 23 + 4 P 6 0 45 0.77 N 0 0 -GT0047+612 0 47 9 + 2 61 15 0 + 144 122 8 -1 3 25 + 5 E 6 0 74 1 .45 N 1 23 N GT0047+617 0 47 42 + 6 61 43 9 + 140 122 8 -0 9 35 + 9 P 6 1 01 1 .47 N 1 34 N GT0049+G26 0 49 12 + 1 62 36 50 ±142 123 0 0 0 38 + 6 E 5 1 15 1 .74 N 0 0 -GT0049+635 O 49 38 + 2 63 30 4 ± 80 123 1 0 9 29 + 5 P 5 0 77 1.21 N 0 O -GT0053+624 0 53 34 + 1 62 25 48 ± 33 123 5 -0 2 48 + 5 1 16 0 91 1 .68 N 0 0 -GT0056+609 0 56 28 + 2 60 54 52 + 80 123 9 -1 7 15 + 3 E 6 0 31 0.56 N 0 0 -GT0056+606 0 56 58 + 3 60 37 25 ±1 17 124 0 -2 0 29 + 6 E 16 0 99 2.43 N 1 57 N GT0057+642 0 57 33 + 8 64 14 1 ± 64 123 9 1 6 67 + 8 P 6 0 81 1.41 N 0 0 -GT0058+642 0 58 46 + 2 64 14 19 + 80 124 1 1 7 50 + 11 P 1 - - - 0 0 -GT0059+636 0 59 31 + 3 63 36 8 ± 62 124 2 1 0 45 + 7 P 6 0 71 1 .34 N 0 02 N GTOIOO+628 1 0 23 + 2 62 51 4 ±123 124 3 0 3 26 + 6 P 2 0 63 0.64 N 0 0 -GTO100+605 1 0 35 + 2 60 32 54 ±1 18 124 4 -2 0 18 + 3 P 6 0 96 1 .82 N 0 0 -GT0101+615 1 1 16 + 4 61 33 1 1 ± 85 124 5 -1 0 19 + 4 P 15 0 86 1 .74 N 0 0 N GT0102+622 1 2 37 + 2 62 12 40 ± 59 124 6 -0 3 49 + 7 P 16 0 87 2.11 N 1 35 N GT0102+629 1 2 43 + 2 62 55 13 ± 95 124 6 0 4 28 + 5 P 3 0 51 0.73 N 0 0 -GT0103+631 1 3 15 + 1 63 10 24 ± 50 124 6 0 6 212 + 22 2 16 1 21 2.29 N 1 38 N BG 0103+63 GTO105+605 1 5 21 + 8 60 35 21 ±137 125 0 -1 9 20 + 5 E 5 0 97 1 .58 N 0 0 -GT0105+610 1 5 37 + 6 61 4 54 ± 40 125 0 -1 5 79 + 11 3 16 0 65 1 .00 N 1 77 N 4C 61.01 GTO106+612 1 6 38 + 1 61 17 29 ± 22 125 1 -1 2 285 + 29 P 16 1 63 3.11 P 13 03 Y GT0108+626 1 8 59 + 2 62 38 36 ± 59 125 3 0 1 28 + 5 P 5 0 25 0.35 N 0 0 -GT0109+608 1 9 9 + 2 60 51 35 ± 67 125 5 -1 6 25 + 4 P 6 0 75 1.12 N 0 0 -GT0109+613 1 9 22 + 7 61 20 37 ±125 125 4 - 1 2 90 + 17 P 5 0 89 1 .36 N 1 51 N GT0110+621 1 10 41 + 1 62 8 47 ± 43 125 5 -0 3 131 + 16 1 5 0 98 1 . 14 N 0 66 N 4C 62.02 GT0112+636 1 12 19 + 2 63 40 3 ±1 14 125 6 1. 2 17 + 4 E 6 0 37 0.61 N 0 0 -GT0114+610 1 14 36 + 2 61 0 22 ±116 126 1 -1 4 25 + 5 E 16 0 98 1 .79 N 0 0 N GT0115+605 1 15 0 + 2 60 35 51 ± 66 126 2 -1 8 29 + 6 P 2 1 21 1 .25 N 0. 0 -GT0116+622 1 16 9 + 2 62 13 15 ± 47 126 2 -0. 2 67 + 9 E 16 1 01 1 .96 N 3 61 Y T a b l e V I . C o n t i n u e d NAME RA(1950) h m s DEC(1950) 1 b F l u x Dens l ' ty (mdy) Diam No. Shor t V . V a r l a t I o n s Term V i VAR? Long Index Term VAR7 O t h e r C a t a l o g u e s GT0118+607 1 18 39 + 2 60 44 30 + 67 126 6 - 1 7 34 + 5 P 5 0 43 0 70 N O 0 GT0118+603 1 18 43 + 2 60 22 28 ±196 126 7 -2 0 21 + 4 E 5 0 64 0 97 N 0 0 -GTO118+609 1 18 58 + 3 60 55 37 + 170 126 6 -1 5 60 + 12 P 6 0 93 1 68 N 1 64 N GTO120+610 1 20 34 + 1 61 0 51 ± 60 126 8 - 1 4 63 + 7 3 16 0 89 2 20 N 0 0 -GT0121+643 1 21 27 + 3 64 18 47 ±134 126 5 1 9 26 + 7 E 2 0 40 0 44 N 0 0 -GT0121+637 1 21 44 + 2 63 43 2 ± .84 126 6 1 3 45 + 7 E 2 0 75 0 77 N 0 0 -GT0122+644 1 22 18 + 8 64 24 4 ± 77 126 6 2 0 64 + 12 2 16 0 67 1 14 N 1 05 N GT0122+639 1 22 44 + 8 63 58 14 ± 43 126 7 1 6 68 + 11 P 16 0 85 2 65 N 1 50 N GT0123+616 1 23 35 + 8 61 36 22 ± 60 127 1 - 0 7 56 + 12 2 16 0 64 1 48 N 1 48 N GT0124+613 1 24 17 + 1 61 19 2 + 46 127 2 -1 0 129 + 16 4 5 0 40 0 59 N 0 60 N GT0124+603 1 24 34 + 5 60 18 48 + 118 127 4 -2 0 24 + 6 E 4 0 34 0 50 N 0 0 -GT0124+632 1 24 40 + 1 63 12 48 ± 66 127 0 0 9 104 + 12 5 2 0 94 0 99 N 0 0 -GT0125+628 1 25 9 + 1 62 50 33 ± 21 127 1 0 5 543 + 54 P 5 0 34 0 59 N 0 55 N GT0125+642 1 25 38 + 8 64 12 54 ± 55 127 0 1 9 47 + 10 P 5 0 87 1 54 N 0 53 N GT0125+639 1 25 52 + 6 63 59 24 ± 67 127 0 1 7 35 + 6 P 6 0 63 1 15 N 0 0 N GT0126+635 1 26 1 1 + 2 63 35 19 ±105 127 1 1 3 27 + 5 P 4 0 46 0 69 N 0 0 -GT0127+608 1 27 17 + 2 60 52 30 ±10'1 127 6 - 1 4 18 + 3 E 6 0 71 1 22 N 0 0 -GT0128+604 1 28 27 + 2 60 24 19 ± 47 127 9 - 1 8 59 + 7 P 6 0 73 1 30 N 2 10 N GT0128+616 1 28 52 + 2 61 38 27 + 94 127 7 - 0 6 32 + 7 P 2 0 39 0 50 N 1 63 N GT0129+624 1 29 19 + 2 62 27 4 ± 70 127 6 0 2 41 + 8 P 5 1 01 1 78 N 1 28 N GT0129+613 1 29 20 + 2 61 18 42 ± 47 127 8 - 0 9 56 + 7 P 6 1 01 1 47 N 2 56 N GT0130+627 1 30 21 + 2 62 45 12 ± 88 127 7 0 5 48 + 9 P 1 - - - 0 0 ~ GT0130+636 1 30 51 + 2 63 41 31 ± 45 127 6 1 5 70 + 10 P 1 - - - 0 0 GT0132+619 1 32 24 + 8 61 55 36 + 102 128 1 - 0 2 53 + 12 E 6 0 86 1 65 N 0 25 N GT0132+610 1 32 59 + 1 61 0 52 ± 63 128 3 -1 1 73 + 10 P 6 0 44 0 64 N 3 45 P GT0133+602 1 33 31 + 8 60 17 37 ± 54 128 5 -1 8 99 + 15 E 6 0 54 0 82 N 0 0 N GT0133+612 1 33 52 + 1 61 13 28 ± 45 128 4 - 0 9 95 + 10 2 6 0 78 1 34 N 2 28 N GT0134+620 1 34 36 + 4 62 1 39 ±102 128 3 - 0 1 40 + 9 P 1 - - - 0 0 ~ GT0134+627 1 34 41 + 2 62 44 3 + 59 128 2 0 6 58 + 7 P 6 0 81 1 20 N 1 25 N GTO134+640 1 34 56 + 5 64 1 59 ±198 128 0 1 9 19 + 4 E 6 0 76 1 05 N 0 0 -GT0136+628 1 36 24 + 2 62 49 36 + 198 128 4 0 7 22 + 4 E 6 0 78 1 09 N 0 O -GT0137+602 1 37 57 + 2 60 14 37 ± 75 129 0 -1 8 42 + 8 P 1 - - - 0 0 -GT0138+62O 1 38 27 + 2 62 4 41 ± 98 128 8 0 0 28 + 5 P 5 0 10 0 21 N 0 0 -GT0139+621 1 39 6 + 1 62 6 34 ±120 128 8 0 1 35 + 5 P 6 0 81 1 39 N 0 0 -GTO140+607 • 1 40 46 + 2 60 47 49 ±171 129 3 -1 2 30 + 4 P 6 0 61 1 09 N 0 0 -GTO141+605 1 41 26 + 4 60 32 36 ± 65 • 129 4 -1 4 31 + 5 P 5 0 30 0 46 N 0 0 -GT0144+637 1 44 42 + 1 63 46 1 ± 45 129 1 1 8 27 + 3 2 16 0 97 2 69 N 0 0 -GT0148+637 1 48 34 + 2 63 42 30 ± 90 129 5 1 9 23 + 4 E 6 0 66 0 97 N 0 0 -GT0149+625 1 49 35 + 4 62 30 13 ± 47 129 9 0 7 32 + 5 P 5 0 64 0 99 N 0 0 -GT0151+603 1 51 53 + 1 60 21 39 ± 74 130 7 -1 3 72 + 9 P 4 0 36 0 62 N 0 25 N GT0152+620 1 52 22 + 8 62 3 39 ± 48 130 3 0 4 49 + 1 1 P 5 1 33 2 37 N 1 00 N GT0152+617 1 52 33 + 8 61 44 5 ± 65 130 4 0 1 49 + 10 P 6 0 12 0 28 N 1 59 N GT0154+630 1 54 1 + 2 63 5 17 ± 54 130 3 1 4 84 + 10 3 4 0 59 0 97 N 0 62 N PK 130+01.1 t o CO Table V I . Continued NAME RA(1950) h m s DEC(1950) 1 b Flux Density (mdy) Dlam No. Short V i VarlatIons Term V i VAR? Long Index Term VAR? Other Catalogues GT0155+607 1 55 6 + 1 60 47 6 ± 52 131 0 -0 8 60 + 8 2 4 0 50 0.88 N 0 46 N GT0156+622 1 56 33 + 4 62 12 26 ±193 130 8 0 6 48 + 1 1 P 6 0 67 1 . 19 N 0 37 N GTO156+608 1 56 38 + 1 60 49 37 ±145 131 2 -0 7 49 + 7 E 4 0 58 0.91 N 0 88 N GT0157+635 1 57 15 + 1 63 35 13 + 81 130 5 2 0 86 + 13 P 6 0 76 1 .66 N 0 97 N GT0157+613 1 57 21 + 8 61 21 57 ± 33 131 1 -0 2 121 + 14 8 15 0 62 1 . 18 N 2 36 N 4C 61 .03 GT0157+629 1 57 49 + 8 62 59 23 ±113 130 7 1 4 48 + 8 P 6 0 91 1 .45 N 0 80 N GT0158+623 1 58 13 + 1 62 23 27 + 46 130 9 0 9 1 16 + 15 P 15 1 19 2. 19 N 2 76 N GT0159+634 1 59 10 + 3 63 26 1 1 ± 57 130 8 1 9 46 + 1 1 P 16 0 39 0.76 N 0 32 N GT0159+620 1 59 33 + 1 62 1 16 ± 33. 131 2 0 5 128 + 14 P 16 0 98 2.57 N 0 03 N 4C 62.04 GT0201+630 2 1 39 + 1 63 3 41 ± 70 131 1 1 6 72 + 12 P 6 0 85 1 .69 N 2 36 N GT0202+625 2 2 48 + 1 62 30 28 ± 25 131 4 1 1 141 + 14 P 16 1 04 2.44 N 7 32 Y GT0203+605 2 3 48 + 5 60 30 16 + 79 132 1 -0 8 37 + 9 P 2 0 81 0.92 N 0 0 -GT0204+617 2 4 2 + 3 61 47 50 ±198 131 7 0 5 25 + 6 P 2 0 57 0.62 N 0 0 -GT0204+605 2 4 29 + 1 60 32 6 ± 20 132 2 -0 7 628 + 63 P 5 0 55 0.80 N 2 72 N GT0205+604 2 5 5 + 6 60 27 1 1 ± 79 132 2 -0 8 16 + 4 E 6 0 74 1 . 12 N 0 0 N GT0205+596 2 5 1 1 + 2 59 41 57 ±171 132 5 -1 5 30 + 7 P 5 0 46 0.79 N 0 84 N GT0205+614 2 5 57 + 1 61 26 54 ± 22 132 1 0 2 429 • 43 P 5 0 42 0.74 N 0 47 N 4C 61 .04 GT0206+595 2 6 0 + 6 59 30 7 ± 71 132 6 -1 7 37 + 7 E 16 0 87 2.07 N 0 99 N GT0206+632 2 6 23 ± 2 63 17 1 ± 86 131 6 2 0 52 + 9 P 6 0 57 1 .02 N 0 40 N GT0209+603 2 9 16 + 2 60 23 50 ± 65 132 8 -0 7 23 + 5 P 3 0 22 0.26 N 0 0 -GT0210+611a 2 10 13 + 2 61 7 21 ± 58 132 6 0 0 42 + 10 P 1 - - - 0 0 -GT0210+599 2 10 19 + 1 59 59 40 ± 22 133 0 - 1 0 329 + 33 2 5 0 59 1 . 20 N 0 45 N 4C 60.05 GT0210+607 2 10 22 + 2 60 47 33 ±160 132 8 -0 3 26 + 7 P 2 1 00 1 .01 N 0 0 -GT0210+611b 2 10 48 + 2 61 7 46 + 194 132 7 0 1 39 + 6 E 5 1 16 1 . 73 N 0 O -GT0211+631 2 11 18 + 1 63 6 16 + 29 132 2 2 0 177 + 19 1 5 0 55 0.96 N 0 29 N GT0211+615 2 1 1 18 + 4 61 34 37 ±198 132 6 0 5 32 + 5 P 6 0 57 1 .20 N 0 0 -GT0212+629 2 12 19 + 1 62 57 12 ± 82 132 3 1 9 38 + 6 P 5 0 90 1 .60 N 0 0 -GT0213+598 2 13 27 + 4 59 53 17 ±198 133 4 -1 0 49 + 1 1 E 1 - - - 0 0 -GT0214+605 2 14 8 + 5 60 33 16 ± 98 133 3 -0 3 31 + 7 P 16 O 77 1 .43 N 1 24 N GT0214+588 2 14 26 + 1 58 51 36 + 27 133 9 -1 9 137 + 14 2 7 1 07 1 .66 N 1 89 N GT0215+604 2 15 4 + 8 60 27 1 1 + 50 133 4 -0 4 52 + 11 P 5 0 55 0.89 N 0 0 -GT0215+601 2 15 40 + 8 60 10 5 ±103 133 6 -0 6 31 + 7 P 16 0 79 1 . 13 N 1 65 N GT0216+608 2 16 10 + 1 60 53 40 ± 22 133 4 0 1 642 + 64 6 5 0 82 1 .59 N 0 0 - BG 0216+60 GT0216+626 2 16 15 + 2 62 37 20 ±192 132 8 1 7 29 + 5 E 5 0 68 1 .25 N 0 0 -GT0218+599 2 18 10 + 1 59 56 49 ± 28 134 0 -0 7 105 + 1 1 P 5 0 77 1 . 15 N 1 09 N GT0219+602 2 19 10 + 3 60 17 11 ±106 134 0 -0 4 34 + 8 P 6 0 84 1 .69 N 1 22 N GT0219+589 2 19 59 + 2 58 54 1 1 ± 99 134 5 -1 7 35 + 6 E 2 0 26 0.31 N 0 0 -GT0221+606 2 21 59 + 2 60 41 31 ±109 134 1 0 1 33 + 5 E 4 0 83 1 .48 N 0 0 -GT0222+596 2 22 5 + 1 59 40 43 ± 41 134 5 -0 8 59 + 6 E 6 0 79 1 . 19 N 0 0 -GT0223+593 2 23 48 + 4 59 21 53 ± 96 134 8 -1 0 19 + 4 E 16 0 49 1 .00 N 0 0 N GT0226+591 2 26 58 + 2 59 7 47 + 75 135 3 -1 1 24 + 4 P 6 0 80 1 .59 N 0 0 - — GT0228+585 2 28 43 + 6 58 32 38 ± 72 135 7 -1 6 37 + 7 E 14 1 01 2.02 N 1 06 N GT0231+597 2 31 50 + 1 59 43 32 ± 30 135 6 -0 3 124 + 13 P 5 1 39 2.07 N 1 04 N WE 0231+59W3 t o VD T a b l e V I . C o n t i n u e d NAME R A ( 1 9 5 0 ) h m s D E C ( 1 9 5 0 ) F l u x D e n s i t y ( m J y ) D l a m N o . V a r i a t i o n s S h o r t T e r m V i V» V A R ? L o n g T e r m I n d e x V A R ? O t h e r C a t a l o g u e s G T 0 2 3 3 + 5 7 9 2 3 3 48 + 2 5 7 5 6 34 ± 1 1 2 136 6 -1 9 5 6 + 1 1 P 12 0 57 1 0 1 N 2 6 5 N G T 0 2 3 4 + 5 8 9 2 34 15 + 1 5 8 5 8 51 ± 25 136 2 - 0 9 9 4 8 + 9 5 P 12 1 34 2 4 9 N 0 61 N G T 0 2 3 6 + 6 1 0 2 3 6 4 0 + 4 61 1 52 ± 9 9 135 7 1 1 168 + 27 P 12 8 22 16 9 8 Y 3 33 P G T 0 2 3 6 + 5 9 8 2 3 6 58 + 2 5 9 51 10 ± 6 5 136 2 0 0 28 + 6 P 2 0 10 0 14 N 0 0 -G T 0 2 4 2 + 5 8 0 2 4 2 27 + 2 58 0 3 3 + 72 137 6 - 1 4 32 + 5 P 14 0 6 7 1 3 2 N 0 4 6 N G T 0 2 4 5 + 5 9 0 2 4 5 4 0 + 8 5 9 1 25 ± 1 9 8 137 5 - 0 3 3 0 + 6 P 5 0 2 9 0 4 3 N 0 0 -G T 0 2 4 6 + 5 7 7 2 4 6 36 + 1 57 44 34 ± 8 6 138 2 -1 4 72 + 9 P 5 0 27 0 4 7 N 1 4 3 N G T 0 2 4 7 + 5 7 2 2 4 7 6 + 3 5 7 13 15 ± 88 138 5 -1 8 34 + 6 E 15 0 8 3 1 4 9 N 0 0 9 N G T 0 2 4 7 + 5 8 8 2 4 7 44 + 3 5 8 52 3 5 ± 62 137 8 - 0 3 23 + 5 P 5 0 35 0 6 6 N 0 0 -G T 0 2 5 0 + 5 8 9 2 5 0 1 + 2 5 8 5 7 38 ± 1 8 7 138 1 - 0 1 25 + 4 E 4 0 5 3 0 9 1 N 0 0 -G T 0 2 5 1 + 5 8 0 2 51 7 + 1 58 5 13 ± 56 138 6 - 0 8 47 + 6 2 6 1 21 1 6 3 N 0 0 -G T 0 2 5 1 + 5 7 4 2 51 22 + 1 5 7 28 15 ± 37 138 9 -1 3 74 + 8 2 6 0 8 0 1 6 4 N . 1 4 5 N G T 0 2 5 1 + 5 7 8 2 51 42 + 7 5 7 4 8 27 ± 1 9 8 138 8 -1 0 18 + 4 P 5 0 2 5 0 5 5 N 0 0 -G T 0 2 5 2 + 5 8 6 2 52 27 + 4 5 8 38 4 2 ± 87 138 5 - 0 2 21 + 6 P 2 0 7 0 0 74 N 0 0 -G T 0 2 5 2 + 5 7 4 2 5 2 42 + 1 57 24 2 5 ± 26 139 1 -1 3 156 + 16 P 15 1 2 9 2 4 2 N 11 36 Y G T 0 2 5 4 + 5 9 1 2 54 3 + 1 5 9 10 13 ± 57 138 4 0 4 155 + 18 P 5 1 0 2 1 3 8 N 0 19 N G T 0 2 5 5 + 5 7 4 2 5 5 51 + 1 5 7 27 4 7 ± 26 139 4 -1 0 2 0 4 + 21 P 7 1 0 2 1 8 0 N 3 4 3 P G T 0 2 5 7 + 5 8 2 2 5 7 48 + 2 5 8 16 5 + 157 139 3 - 0 2 28 + 5 P 15 0 84 1 7 8 N 0 5 5 N G T 0 2 5 9 + 5 8 5 2 5 9 4 ± 1 5 8 34 3 8 ± 44 139 3 0 1 38 + 4 P 6 0 4 6 0 84 N 0 0 -G T 0 2 5 9 + 5 7 2 2 5 9 4 0 + 3 57 15 9 + 116 140 0 -1 0 28 + 7 P 5 0 87 1 4 6 N 0 15 N G T 0 2 5 9 + 5 7 6 2 5 9 48 + 2 57 41 1 1 ± 47 139 8 - 0 6 15 + 3 P 5 0 87 1 5 6 N 0 0 -G T 0 3 0 0 + 5 7 8 3 0 43 + 4 5 7 5 0 24 ± 1 0 3 139 8 - 0 4 28 + 6 E 7 0 4 8 0 74 N 0 19 N G T 0 3 0 0 + 5 7 5 3 0 58 ± 2 5 7 3 0 3 9 ± 1 16 140 0 - 0 7 27 + 7 P 7 1 5 6 2 2 6 N 0 0 N G T 0 3 0 1 + 5 7 0 3 1 48 + 1 5 7 4 2 5 + 37 140 3 -1 0 6 5 + 7 2 6 0 8 9 1 4 8 N 2 3 6 N G T 0 3 0 1 + 5 6 4 3 1 5 3 + 2 5 6 2 6 5 7 ± 8 9 1 4 0 6 -1 5 34 + 5 E 6 0 84 1 5 7 N 2 4 5 N G T 0 3 0 2 + 5 7 7 3 2 4 + 1 5 7 4 6 5 + 38 140 0 - 0 4 41 + 6 P 6 0 8 5 1 8 3 N 1 51 N G T 0 3 0 4 + 5 7 5 3 4 18 + 1 5 7 3 0 31 ± 28 140 4 - 0 5 2 0 4 + 21 P 5 0 5 8 0 8 3 N 7 6 6 Y G T 0 3 0 4 + 5 8 8 3 4 19 + 2 5 8 4 9 2 3 ± 54 139 8 0 7 2 5 + 5 P 3 0 3 3 0 4 6 N 0 0 -G T 0 3 0 5 + 5 6 5 3 5 17 + 1 5 6 31 33 ± 28 141 0 -1 2 138 + 16 P 6 0 9 0 1 54 N 1 34 N G T 0 3 0 5 + 5 7 7 3 5 52 + 5 57 4 6 5 2 ± 98 140 4 - 0 1 16 • 4 P 6 0 4 8 0 7 6 N 2 4 0 N G T 0 3 0 6 + 5 7 1 3 6 23 + 2 57 6 41 + 6 8 140 8 - 0 7 32 + 5 P 2 0 72 0 7 9 N d 0 -G T 0 3 0 6 + 5 6 6 3 6 28 + 1 5 6 38 26 ± 28 141 1 -1 1 131 + 14 P 5 0 41 0 8 3 N 0 0 -G T 0 3 0 6 + 5 9 2 3 6 56 + 2 5 9 14 35 ± 1 6 2 139 8 1 2 3 0 + 7 P 2 0 4 0 0 4 3 N 0 0 -G T 0 3 0 6 + 5 9 5 3 6 57 + 8 5 9 33 2 5 ± 1 9 8 139 7 1 5 19 + 5 E 5 0 0 7 0 19 N 0 0 -G T 0 3 0 6 + 5 7 7 3 6 57 + 2 5 7 4 6 37 ± 1 3 0 1 4 0 6 - 0 1 18 + 4 E 3 0 58 0 84 N 0 0 -G T 0 3 0 8 + 5 8 5 3 8 4 + 1 5 8 3 0 4 8 + 103 140 3 0 7 5 9 + 9 P 6 0 72 1 3 3 N 1 8 9 N G T 0 3 0 9 + 5 5 7 3 9 19 + 3 5 5 4 5 17 ± 1 5 4 141 9 -1 6 16 ± 3 P 4 1 41 1 3 8 N 0 0 -G T O S 0 9 + 5 7 6 3 9 22 + 1 5 7 41 4 6 ± 75 140 9 0 0 29 + 5 P 6 1 12 1 8 4 N 0 0 -G T 0 3 0 9 + 5 6 3 3 9 57 + 8 56 18 4 6 ± 4 3 141 7 -1 1 8 6 + 21 P 2 0 51 0 51 N 0 24 N G T 0 3 1 0 + 5 6 5 3 10 6 + 1 5 6 3 0 0 ± 3 0 141 6 - 0 9 75 + 9 P 6 1 0 7 2 0 1 N 2 8 6 N G T 0 3 1 0 + 5 6 0 3 10 42 + 8 5 6 3 13 ± 34 141 9 -1 3 177 + 24 1 5 0 6 0 0 8 7 N 0 5 5 N G T 0 3 1 0 + 5 6 4 3 10 53 + 3 5 6 26 27 ± 1 9 8 141 7 - 0 9 2 3 + 5 E 5 0 9 6 1 5 7 N 0 6 8 N G T 0 3 1 2 + 5 8 9 3 12 2 + 2 5 8 5 9 44 ± 1 2 8 140 5 1 3 22 + 5 E 2 0 11 0 1 1 N 0 0 -4 C 5 8 . 0 8 T a b l e V I . C o n t i n u e d NAME R A ( 1 9 5 0 ) h m s D E C ( 1 9 5 0 ) 1 b F l u x D e n s i t y ( m d y ) D 1am N o . S h o r t V i V a r 1 a t I o n s T e r m V , V A R ? L o n g I n d e x T e r m V A R ? O t h e r C a t a l o g u e s G T 0 3 1 2 + 5 7 7 3 12 4 + 8 57 4 6 13 8 2 141 2 0 3 27 + 7 P 4 0 . 8 6 1 2 8 N 0 2 5 N 4C 5 8 . 0 9 G T 0 3 1 2 + 5 8 9 3 12 38 + 1 5 8 5 5 13 + 43 140 6 1 3 121 + 14 P 4 0 . 3 7 0 6 6 N 0 9 0 N G T 0 3 1 2 + 5 9 4 3 12 57 + 2 5 9 28 34 ± 1 2 0 140 4 1 8 26 + 5 P 3 0 8 2 1 21 N 0 0 ~~ G T 0 3 1 3 + 5 9 1 3 13 36 + 2 5 9 7 2 + 81 140 6 1 5 2 9 + 5 P 3 0 6 7 0 9 5 N 0 0 -G T 0 3 1 3 + 5 8 5 3 13 55 + 2 5 8 31 6 + 81 141 0 1 1 19 + 4 P 3 0 51 0 6 9 N O 0 G T 0 3 14 + 5 6 5 3 14 4 + 1 5 6 33 19 + 24 142 0 - 0 6 244 + 2 5 1 4 1 0 2 1 5 6 N 8 4 8 V G T 0 3 1 4 + 5 5 3 3 14 52 + 8 5 5 2 0 19 ± 1 9 8 142 8 - 1 6 18 + 4 E 5 0 3 6 0 5 6 N 0 0 -G T 0 3 1 5 + 5 5 3 3 15 42 + 2 5 5 19 4 0 ± 1 8 6 142 9 - 1 5 24 + 4 P 3 1 0 7 1 41 N 0 0 ~ G T 0 3 1 5 + 5 5 8 3 15 55 + 2 5 5 5 0 18 + 5 9 142 6 -1 1 26 + 5 P 5 0 3 0 0 4 2 N 0 7 9 N G T 0 3 1 6 + 5 7 O 3 16 1 + 2 57 2 1 + 9 6 142 0 - 0 1 37 + 6 P 5 1 15 1 81 N 0 9 0 N G T 0 3 1 6 + 5 8 5 3 16 19 + 3 5 8 31 4 8 + 100 141 2 1 2 2 9 + .7 P 2 0 0 3 0 10 N 0 0 ~ G T 0 3 1 6 + 5 7 7 3 16 27 + 1 5 7 47 27 + 4 7 141 6 0 6 6 3 + 8 P 5 0 5 7 0 6 9 N 0 0 8 N G T 0 3 1 7 + 5 8 6 3 17 1 1 + 2 5 8 36 4 6 + 6 7 141 3 1 4 21 + 5 P 4 0 91 1 3 0 N 0 11 N G T 0 3 1 7 + 5 7 3 3 17 45 + 1 5 7 19 10 + 39 142 0 0 3 120 + 14 2 5 1 0 5 1 61 N 1 81 N G T 0 3 1 8 + 5 8 4 3 18 37 + 8 5 8 24 25 + 9 0 141 6 1 3 9 2 + 17 P 3 0 2 5 0 34 N 0 15 N G T 0 3 1 9 + 5 5 5 3 19 19 + 3 5 5 31 28 + 47 143 2 -1 1 62 + 8 P 2 0 5 0 0 6 0 N 0 0 -G T 0 3 1 9 + 5 4 9 3 19 22 + 1 54 5 6 4 0 + 3 0 143 5 -1 6 8 2 + 7 P 5 0 5 7 1 10 N 0 0 G T 0 3 2 1 + 5 7 7 3 21 1 1 + 3 5 7 44 18 + 52 142 2 0 9 62 + 8 P 2 0 0 5 0 15 N 0 0 G T 0 3 2 1 + 5 8 5 3 21 12 + 3 5 8 35 6 + 31 141 7 1 6 4 5 + 5 P 5 0 7 9 1 37 N 0 0 G T 0 3 2 1 + 5 8 9 3 21 24 + 1 5 8 5 7 13 + 5 5 141 6 1 9 34 + 4 P 5 0 4 5 0 74 N 0 0 OE+537 G T 0 3 2 2 + 5 7 4 3 2 2 44 + 1 57 2 9 12 + 24 142 5 0 8 198 + 16 1 2 0 0 0 0 4 N 0 0 • G T 0 3 2 3 + 5 6 3 3 2 3 9 + 2 5 6 18 4 9 + 6 3 143 2 - 0 1 47 ± 5 P 5 0 3 0 0 5 2 N 0 0 WK105 G T 0 3 2 3 + 5 6 0 3 2 3 45 + 1 5 6 5 2 + 26 143 4 - 0 3 157 ± 13 1 3 0 3 6 0 4 8 N 0 0 G T 0 3 2 4 + 5 4 9 3 24 2 0 + 1 54 5 8 4 8 + 22 144 1 -1 1 170 + 13 P 5 1 38 2 4 0 N 0 0 ~ H B 0 7 G T 0 3 2 4 + 5 4 5 3 24 48 + 2 54 34 19 + 79 144 4 -1 4 4 5 + 8 P 3 0 15 0 31 N 0 2 8 N 4C 5 5 . 0 7 G T 0 3 2 8 + 5 5 7 3 2 8 27 + 1 5 5 4 5 17 + 22 144 1 - 0 2 177 + 14 2 3 0 81 1 0 9 N 0 0 -G T 0 3 2 9 + 5 4 0 3 2 9 57 + 2 54 5 3 0 + 8 6 145 3 -1 4 29 + 5 P 6 0 74 1 15 N 0 19 N G T 0 3 3 0 + 5 7 3 3 3 0 14 ± 2 5 7 22 4 8 ± 1 2 6 143 4 1 3 19 + 4 E 5 0 9 4 1 31 N 2 54 N G T 0 3 3 0 + 5 5 9 3 3 0 32 + 8 5 5 5 6 4 5 84 144 3 0 1 44 + 12 E 6 0 6 2 1 0 7 N 1 0 5 N G T 0 3 3 1 + 5 7 6 3 31 3 + 2 57 38 37 + 101 143 4 1 6 28 + 4 P 5 0 5 9 0 9 0 N 0 0 N G T 0 3 3 1 + 5 7 2 3 31 16 + 1 57 14 5 6 + 5 9 143 6 1 3 51 + 6 6 6 0 6 3 1 0 1 N 2 7 6 G T 0 3 3 3 + 5 5 5 3 3 3 25 + 1 5 5 32 2 + 5 0 144 8 0 0 4 6 + 6 E 4 1 10 1 5 2 N 0 22 N G T 0 3 3 3 + 5 3 8 3 3 3 57 + 1 5 3 4 8 17 ± 26 145 9 -1 3 94 + 10 P 6 0 38 0 61 N 1 7 5 N G T 0 3 3 4 + 5 3 3 3 34 10 + 2 5 3 19 3 3 + 9 6 146 2 -1 7 32 + 5 P 5 0 78 1 0 8 N 0 2 6 N G T 0 3 3 4 + 5 3 7 3 34 22 + 2 5 3 4 6 38 + 84 146 0 -1 3 19 + 4 P 5 0 7 0 1 2 3 N 0 0 -G T 0 3 3 4 + 5 4 9 3 34 29 + 2 54 57 5 5 + 5 9 145 3 -o 3 21 + 3 P 5 0 4 7 0 7 9 N 0 0 ~~ G T 0 3 3 4 + 5 6 5 3 34 44 + 6 5 6 31 5 ± 9 5 144 4 1 0 71 + 12 P 5 1 0 4 1 7 5 N 0 51 N G T 0 3 3 5 + 5 7 2 3 3 5 8 + 2 5 7 15 51 + 8 5 144 0 1 6 34 ± 7 P 5 0 8 0 1 3 5 N 1 0 3 N G T 0 3 3 5 + 5 5 8 3 35 17 + 1 5 5 48 39 + 23 144 9 0 4 2 2 0 + 22 2 5 0 8 3 1 44 N 0 0 "* G T 0 3 3 5 + 5 6 8 3 3 5 28 + 1 5 6 51 5 + 9 0 144 3 1 3 6 6 + 10 P 5 0 7 0 1 32 N 1 7 8 N G T 0 3 3 5 + 5 5 3 3 3 5 45 + 1 5 5 23 15 • 3 0 145 2 0 1 101 + 1 1 P 4 1 0 8 1 4 5 N 0 . 6 3 N G T 0 3 3 5 + 5 7 2 3 3 5 55 + 2 5 7 17 6 + 5 3 144 1 1 7 45 + 6 P 5 0 37 0 6 2 N 1 9 7 N G T 0 3 3 7 + 5 5 6 3 37 1 + 5 5 5 36 54 ± 1 10 145 . 2 0 4 14 + 4 P 5 0 7 2 1 0 9 N 0 . 0 T a b l e V I . C o n t i n u e d NAME R A ( 1 9 5 0 ) h m s O E C ( 1 9 5 0 ) * t II 1 b F l u x D e n s i t y ( m J y ) D1am N o . S h o r t V i V a r i a t i o n s T e r m V , V A R 7 L o n g I n d e x T e r m V A R ? O t h e r C a t a l o g u e s G T 0 3 3 7 + 5 5 7 3 37 5 5 + 1 5 5 4 6 28 ± 31 145 2 0 6 185 + 2 0 P 4 0 5 7 0 . 8 1 N 1 24 N G T 0 3 3 8 + 5 4 4 3 38 13 + 4 54 28 3 + 76 146 0 - 0 4 18 + 5 P 3 0 8 9 1 . 10 N 0 0 -G T 0 3 3 9 + 5 3 3 3 3 9 7 + 1 5 3 21 2 ± 26 146 8 -1 2 8 9 + 10 P 5 0 47 0 . 7 3 N 1 3 5 N G T 0 3 3 9 + 5 4 6 3 3 9 15 + 8 54 37 47 + 117 146 1 - 0 2 33 + 9 P 2 0 7 6 0 . 7 9 N 0 0 -G T 0 3 3 9 + 5 5 8 3 3 9 57 + 2 5 5 4 8 2 5 + 6 7 145 4 0 8 24 + 4 P 5 0 6 8 0 . 9 9 N 0 0 -G T 0 3 4 2 + 5 5 6 3 4 2 4 + 2 5 5 39 3 0 + 198 145 7 0 9 19 + 4 E 6 0 9 0 1 . 5 3 N 0 4 0 N G T 0 3 4 2 + 5 5 1 3 4 2 2 0 + 1 5 5 6 1 1 ± 35 146 1 0 5 77 + 8 1 6 1 0 8 1 .51 N 0 8 2 N G T 0 3 4 2 + 5 3 8 3 4 2 4 3 + 1 5 3 52 6 + 21 146 9 - 0 5 6 0 2 + 6 0 P 5 0 3 0 0 . 4 2 N 3 2 6 P 0 E + 5 7 0 G T 0 3 4 3 + 5 2 4 3 4 3 42 + 4 52 27 3 6 ± 7 0 147 9 -1 5 21 + 5 P 5 0 31 0 . 5 6 N 1 34 N G T 0 3 4 4 + 5 3 9 3 44 3 + 4 5 3 5 9 8 ± 1 8 3 147 0 - 0 3 13 + 3 P 5 0 6 2 1 . 2 7 N 0 0 -G T 0 3 4 4 + 5 5 5 3 44 25 + 1 5 5 31 2 8 + 74 146 1 1 0 8 3 + 12 E 5 0 74 1 . 2 4 N 1 71 N O E + 5 7 3 G T 0 3 4 4 + 5 3 6 3 44 38 + 2 53 41 3 9 ± 87 147 2 - 0 5 2 5 + 5 P 5 0 9 5 1 • 77 N 0 0 -G T 0 3 4 5 + 5 4 4 3 4 5 3 + 2 54 2 6 27 ± 6 0 146 8 0 2 3 0 + 5 P 5 0 76 1 . 4 2 N 0 0 -G T 0 3 4 5 + 5 4 9 3 4 5 10 + 2 54 57 4 6 ± 1 0 3 146 5 0 6 31 + 5 E 5 0 8 9 1 . 0 8 N 0 0 -G T 0 3 4 5 + 5 5 6 3 4 5 28 + 2 5 5 38 13 ± 38 146 1 1 2 3 9 + 6 P 5 0 8 0 1 . 3 3 N 0 5 5 N G T 0 3 4 6 + 5 5 7 3 4 6 48 + 1 5 5 4 3 0 ± 78 146 2 1 3 4 3 + 7 P 5 1 19 1 . 9 6 N 0 O -G T 0 3 4 7 + 5 4 0 3 4 7 2 + 2 54 1 16 ± 47 14.7 3 0 0 4 0 + 6 E 4 1 0 9 1 . 3 2 N 0 31 N G T 0 3 4 7 + 5 2 6 3 4 7 28 + 2 52 4 0 44 ± 6 3 148 2 -1 0 2 3 + 3 P 6 0 4 8 0 . 9 0 N 0 0 - ' G T 0 3 4 7 + 5 3 3 3 4 7 37 + 8 5 3 2 0 18 ± 58 • 147 8 - 0 5 153 + 28 P 4 0 9 8 1 . 5 5 N 1 18 N CR 5 4 T 0 6 2 G T 0 3 4 8 + 5 2 2 3 4 8 44 + 1 52 13 24 + 42 148 6 -1 2 4 0 + 6 P 4 0 5 5 0 . 7 4 N 1 22 N G T 0 3 4 9 + 5 2 6 3 4 9 17 + 1 5 2 36 12 + 35 148 5 - 0 9 6 6 + 7 P 7 0 54 0 . 8 6 N 0 51 N G T 0 3 4 9 + 5 4 1 3 4 9 25 + 4 54 8 5 ± 39 147 5 0 3 121 + 14 P 4 0 5 6 1 . 0 6 N 0 5 9 N G T 0 3 5 0 + 5 5 4 3 5 0 1 1 + 1 55 2 5 5 4 ± 8 3 146 8 1 4 4 6 + 7 P 4 0 6 8 1 . 10 N 0 5 9 N G T 0 3 5 0 + 5 4 7 3 5 0 3 0 + 4 54 47 16 + 132 147 2 0 9 2 0 ± 5 P 5 0 8 3 1 . 15 N 0 7 0 N G T 0 3 5 1 + 5 4 4 3 51 2 + 1 54 27 16 ± 57 147 5 0 7 4 9 + 8 P 7 0 72 1 . 24 N 1 9 5 N G T 0 3 5 1 + 5 5 8 3 51 3 + 2 5 5 5 2 4 6 ± 1 4 7 146 6 1 8 19 + 4 P 2 0 14 0 . 0 5 N 0 0 -G T 0 3 5 1 + 5 4 3 a 3 51 4 + 8 54 22 19 ± 45 147 6 0 7 2 0 0 ± 1 0 0 P 5 3 47 6 . 6 9 Y 0 0 -G T 0 3 5 1 + 5 4 9 3 51 16 + 6 54 54 4 2 ± 8 6 147 2 1 1 25 + 6 E 5 0 71 1 . 14 N 0 4 3 N G T 0 3 5 1 + 5 4 3 b 3 51 4 5 + 1 54 21 0 ± 22 147 6 0 7 162 + 16 P 7 0 94 1 . 7 4 N 2 51 N G T 0 3 5 3 + 5 2 1 3 5 3 6 + 1 52 8 5 0 ± 3 9 149 2 - 0 9 8 3 + 10 P 4 0 4 0 0 . 7 1 N 1 32 N G T 0 3 5 3 + 5 1 4 3 5 3 17 + 8 51 2 9 2 3 ± 1 0 0 149 7 -1 3 28 + 8 E 7 0 7 5 1 . 10 N 0 0 -G T 0 3 5 3 + 5 3 4 3 5 3 31 + 4 5 3 25 5 2 ± 1 4 8 148 4 0 2 17 + 4 E 4 0 52 0 . 75 N 0 0 -G T 0 3 5 3 + 5 3 9 3 5 3 5 0 + 5 5 3 56 19 ± 1 9 8 148 1 0 6 5 9 + 8 P 4 0 8 8 1 . 33 N 1 9 8 N 0 E + 5 9 0 G T 0 3 5 4 + 5 3 3 3 54 8 + 8 5 3 18 5 0 ± 1 0 9 148 6 0 1 27 + 7 E 5 0 7 0 1 . 17 N 0 0 -G T 0 3 5 4 + 5 2 9 3 54 19 + 3 5 2 54 54 ± 34 148 9 - 0 1 103 + 12 P 7 0 6 3 1 . 15 N 0 10 N G T 0 3 5 4 + 5 4 7 3 54 31 + 2 54 4 5 4 2 ± 8 3 147 7 1 3 18 + 3 P 7 0 28 0 . 5 5 N 0 0 -G T 0 3 5 4 + 5 4 3 3 54 42 + 2 54 18 19 + 123 148 0 1 0 3 0 + 5 P 5 0 4 5 0 . 8 5 N 0 9 7 N 0 E + 5 9 1 G T 0 3 5 6 + 5 3 5 3 5 6 27 + 2 5 3 3 0 16 + 43 148 7 0 5 4 2 + 6 P 5 0 5 5 1 . 15 N 0 8 0 N 4C 5 3 . 0 9 G T 0 3 5 8 + 5 1 8 3 5 8 19 + ' 1 51 4 8 51 ± 71 150 0 - 0 6 75 + 9 4 7 0 8 8 1 . 2 5 N 0 4 2 N 4C 5 1 . 1 1 G T 0 3 5 8 + 5 2 3 3 5 8 28 + 2 52 18 18 ± 81 149 7 - 0 2 71 + 10 4 7 0 5 9 0 . 9 1 N 0 4 3 N G T 0 3 5 8 + 5 3 9 3 5 8 47 + 8 5 3 5 6 2 3 ± 1 1 7 148 7 1 1 32 + 10 E 4 0 4 2 0 . 5 7 N 0 13 N G T 0 3 5 9 + 5 4 5 3 5 9 3 + 8 54 33 4 8 ± 8 9 148 3 1 6 26 + 6 P 4 1 23 1 . 7 8 N 0 0 -G T 0 3 5 9 + 5 3 6 3 5 9 3 0 + 2 5 3 39 4 5 ± 1 1 1 149 0 0 9 2 3 + 5 P 5 0 5 9 1 . 0 1 N 0 4 6 N tvj T a b l e V I . C o n t i n u e d NAME R A ( 1 9 5 0 ) h m s D E C ( 1 9 5 0 ) F l u x D e n s i t y ( m J y ) D 1am N o . V a r l a t I o n s S h o r t T e r m V i V I V A R ? L o n g T e r m I n d e x V A R ? O t h e r C a t a l o g u e s G T 0 3 5 9 + 5 3 3 3 5 9 41 + 1 5 3 19 31 + 28 149 2 0 7 87 + 9 P 7 0 8 3 1 47 N 1 8 9 N G T 0 4 0 0 + 5 2 5 4 0 4 3 + 1 52 3 3 5 9 + 6 8 149 8 0 2 6 7 + 9 P 4 0 6 0 0 8 7 N 1 94 N G T 0 4 0 1 + 5 1 7 4 1 1 1 + 8 51 4 7 24 ± 74 150 4 - 0 3 58 + 12 P 4 0 6 5 1 0 6 N 0 4 9 N G T 0 4 0 1 + 5 2 4 4 1 4 3 ± 2 52 29 24 + 9 3 150 0 0 3 26 + 4 P 7 0 6 0 0 9 0 N 0 0 4 N G T 0 4 0 2 + 5 2 6 4 2 3 + 8 52 41 51 ± 5 5 149 9 0 5 5 6 + 1 1 P 3 0 8 3 1 16 N 0 10 N G T 0 4 0 3 + 5 1 6 4 3 5 + 2 51 4 0 3 0 ± 6 9 150 7 - 0 2 5 0 + 8 P 2 0 4 2 0 54 N 0 0 -G T 0 4 0 4 + 5 2 8 4 4 3 3 + 3 5 2 5 3 5 8 ± 3 9 150 0 0 9 5 9 + 8 P 7 0 81 1 4 9 N 0 8 9 N G T 0 4 0 4 + 5 3 4 4 4 48 + 2 5 3 2 6 37 ± 1 2 2 149 7 1 3 24 + 6 P 2 0 12 0 16 N 0 0 N G T 0 4 0 5 + 5 3 0 4 5 4 5 + 8 5 3 3 6 ± 9 5 150 1 1 1 3 0 + 7 P 2 0 31 0 3 9 N 0 0 -G T 0 4 0 6 + 5 1 6 4 6 23 + 3 51 37 34 ± 39 151 1 0 1 4 0 + 6 P 5 0 3 8 0 51 N 0 3 5 N G T 0 4 0 6 + 4 9 9 4 6 31 ± 1 4 9 54 8 ± 47 152 3 - 1 2 32 + 4 P 4 0 9 0 1 4 0 N 0 0 -G T 0 4 0 7 + 4 9 8 4 7 5 • 1 4 9 4 8 37 ± 44 152 4 -1 2 6 8 + 8 3 5 0 3 8 0 7 5 N 1 6 8 N G T 0 4 0 7 + 4 9 4 4 7 31 + 2 4 9 25 2 3 ± 4 2 152 7 - 1 4 21 + 3 P 7 0 6 8 1 16 N 0 0 -G T 0 4 0 7 + 5 1 0 4 7 52 + 1 51 0 5 9 + 2 0 151 7 - 0 2 1352 ± 1 3 4 4 2 0 5 7 0 6 0 N O 0 -G T 0 4 0 7 + 5 0 3 4 7 5 6 + 2 5 0 2 0 24 ± 6 3 152 1 - 0 7 19 + 3 E 7 0 9 8 1 6 8 N 0 0 -G T 0 4 0 8 + 4 9 4 4 8 3 9 + 1 4 9 2 5 44 ± 47 152 8 -1 3 41 + 6 P 4 0 6 5 0 8 5 N 0 2 5 N G T 0 4 0 8 + 5 3 0 4 8 44 + 3 5 3 3 54 + 153 150 4 1 4 2 6 + 7 P 2 1 21 1 24 N 0 0 -G T 0 4 0 8 + 5 2 8 4 8 56 + 6 52 4 8 51 ± 54 150 6 1 2 4 9 + 10 P 7 0 8 8 1 2 0 N 0 3 0 N G T 0 4 0 9 + 5 2 7 4 9 44 + 1 52 4 3 21 + 21 150 7 1 3 2 6 6 + 27 P 6 0 9 6 1 74 N 1 9 8 N G T 0 4 1O+509 4 10 5 0 + 2 5 0 5 9 39 ± 88 152 0 0 1 1 1 + 3 E 6 0 4 6 0 74 N 0 0 -G T 0 4 1 1 + 5 1 3 4 1 1 22 + 3 51 19 5 6 ± 8 5 151 9 0 4 21 + 4 E 6 0 7 6 1 51 N 0 0 -G T 0 4 1 2 + 4 8 9 4 12 15 + 8 48 57 31 + 76 153 6 -1 2 27 + 8 P 6 0 4 8 0 7 5 N 0 3 6 N G T 0 4 1 3 + 4 9 8 4 13 18 + 1 49 4 9 2 0 ± 1 1 9 153 1 - 0 5 29 + 5 E 5 0 51 0 8 6 N 1 2 6 N G T 0 4 1 3 + 4 9 0 4 13 2 0 + 1 4 9 2 2 9 ± 32 153 7 -1 0 6 7 + 7 P 6 0 8 3 1 77 N 2 34 N G T 0 4 1 3 + 5 1 8 4 13 46 + 2 51 4 9 2 ± 1 4 5 151 8 1 0 46 + 10 P 6 1 10 1 5 9 N 0 17 N G T 0 4 1 3 + 4 9 9 4 13 5 8 + 6 4 9 5 5 36 ± 81 153 1 - 0 3 18 + 5 P 4 0 5 6 0 8 2 N 0 0 -G T 0 4 1 4 + 5 1 2 4 14 16 + 2 51 16 4 6 ± 6 0 152 2 0 7 17 + 4 P 3 0 51 0 6 5 N 0 0 -G T 0 4 1 4 + 5 2 1 4 14 4 2 + 1 52 1 1 2 8 + 44 151 6 1 4 34 + 5 P 6 0 74 1 4 6 N 0 7 0 N G T 0 4 1 4 + 5 1 4 4 14 4 7 + 1 51 27 24 ± 78 152 2 0 9 37 + 6 P 4 0 6 7 1 0 6 N 0 7 6 N G T 0 4 1 5 + 5 0 7 4 15 19 + 8 5 0 4 2 1 + 4 7 152 8 0 4 67 + 12 P 4 0 4 5 O 6 6 N 0 0 -G T 0 4 1 6 + 4 8 9 4 16 2 0 + 2 48 54 5 0 ± 81 154 1 - 0 8 12 + 3 P 6 0 6 6 1 22 N 0 0 -G T 0 4 1 7 + 4 8 4 4 17 3 6 + 8 48 2 9 24 ± 94 154 6 - 0 9 36 + 8 P 3 0 8 9 1 17 N 0 51 N G T 0 4 1 8 + 4 8 3 4 18 9 + 6 4 8 23 21 + 9 9 ' 154 7 - 0 9 23 + 5 E 6 1 41 2 0 8 N 0 71 N G T 0 4 1 9 + 5 0 8 4 19 0 + 2 5 0 52 4 ± 1 2 1 153 1 0 9 27 + 6 E 3 0 5 2 0 74 N 1 84 N G T 0 4 1 9 + 4 9 9 4 19 2 5 + 2 4 9 5 5 16 ± 9 5 153 8 0 3 51 + 7 P 3 0 71 1 01 N 0 0 -G T 0 4 2 0 + 4 9 5 4 2 0 9 + 1 4 9 32 51 ± 39 154 1 0 1 6 6 + 9 P 4 0 5 6 0 74 N 0 19 N G T 0 4 2 1 + 5 0 3 4 21 11 + 4 5 0 19 8 ± 1 9 8 153 7 0 8 16 + 4 P 3 0 3 0 0 5 3 N O 0 -G T 0 4 2 2 + 4 7 8 4 2 2 21 + 2 47 5 2 16 ± 5 6 155 6 - 0 8 18 + 4 P 3 0 0 7 0 16 N 0 0 -G T 0 4 2 2 + 4 9 6 4 22 51 + 1 4 9 41 16 ± 2 5 154 3 0 5 155 17 1 4 0 9 9 1 4 3 N 0 19 N G T 0 4 2 3 + 5 0 2 4 2 3 6 + 4 5 0 12 4 2 ± 1 1 1 154 0 0 9 18 + 4 P 4 0 3 0 0 47 N 1 5 6 N G T 0 4 2 3 + 4 9 5 4 2 3 54 • 8 4 9 32 2 8 ± 1 4 5 154 5 0 5 19 6 P 3 0 3 8 0 4 5 N 0 0 -G T 0 4 2 4 + 4 9 9 4 24 14 + 2 4 9 5 5 58 ± 1 7 2 154 3 0 8 22 + 4 E 5 0 8 8 1 4 2 N 0 19 N G T 0 4 2 4 + 5 0 3 4 24 19 + 3 5 0 22 19 ± 77 154 0 1 2 16 + 4 P 3 0 6 2 0 9 9 N 0 0 -O F + 5 0 4 P R F 2 1 8 B P 0 1 9 T a b l e V I . C o n t i n u e d NAME G T 0 4 2 4 + 5 0 1 G T 0 4 2 5 + 4 8 9 G T 0 4 2 5 + 5 0 2 G T 0 4 2 7 + 4 6 2 G T 0 4 2 8 + 4 9 7 G T 0 4 2 8 + 4 6 8 G T 0 4 3 0 + 4 7 1 G T 0 4 3 0 + 4 9 1 G T 0 4 3 0 + 4 8 5 G T 0 4 3 0 + 4 6 2 G T 0 4 3 1 + 4 7 7 G T 0 4 3 1 + 4 6 2 G T 0 4 3 2 + 4 7 2 G T 0 4 3 3 + 4 8 3 G T 0 4 3 3 + 4 8 8 G T 0 4 3 3 + 4 8 1 G T 0 4 3 3 + 4 7 7 G T 0 4 3 4 + 4 8 0 G T 0 4 3 5 + 4 6 9 G T 0 4 3 5 + 4 8 2 G T 0 4 3 5 + 4 6 4 G T 0 4 3 6 + 4 4 4 G T 0 4 3 8 + 4 6 0 G T 0 4 3 8 + 4 8 5 G T 0 4 3 8 + 4 5 4 G T 0 4 3 8 + 4 7 5 G T 0 4 3 9 + 4 8 2 G T 0 4 3 9 + 4 7 4 G T 0 4 4 0 + 4 5 4 G T 0 4 4 1 + 4 6 6 G T 0 4 4 1 + 4 3 8 G T 0 4 4 1 + 4 4 9 G T 0 4 4 3 + 4 4 3 G T 0 4 4 3 + 4 5 9 G T 0 4 4 5 + 4 5 5 G T 0 4 4 5 + 4 3 6 G T 0 4 4 6 + 4 4 0 G T 0 4 4 6 + 4 3 1 G T 0 4 5 4 + 4 4 5 G T 0 4 5 5 + 4 2 0 G T 0 4 5 5 + 4 3 1 G T 0 4 5 6 + 4 1 2 G T 0 4 5 6 + 4 19 R A ( 1 9 5 0 ) h m s D E C ( 1 9 5 0 ) F l u x D e n s i t y ( m J y ) 01 a m 4 24 35 + 5 5 0 10 4 9 ± 1 9 1 154 . 2 1 . 1 2 0 + 5 E 4 0 . 84 1 . 4 5 N 0 . 2 5 4 2 5 1 + 2 4 8 5 5 0 ± 81 1 5 5 . 1 0 . 2 44 + 7 P 4 0 . 73 1 . 0 9 N 1 . 18 4 2 5 12 + 1 5 0 13 14 ± 21 154 . 2 1 . 2 304 + 31 P 6 0 . 6 9 1 . 21 N 0 . 9 7 4 27 52 + 1 4 6 12 34 ± 23 157 . 4 -1 . 3 167 + 17 P 5 1 . 34 2 . 3 5 N 1 3 . 10 4 28 12 + 1 4 9 43 5 5 ± 3 0 154 . 9 1 . 2 100 + 12 P 4 0 . 5 9 0 . 77 N 0 . 3 5 4 2 8 25 + 1 46 49 3 3 ± 53 157 . 0 - 0 . 8 35 + 5 P 3 O . 5 2 0 . 6 8 N 2 . 3 5 4 3 0 25 + 1 47 8 10 ± 1 2 3 157 0 - 0 . 3 4 3 + 7 P 4 0 . 27 0 . 37 N 1 . 0 8 4 3 0 28 + 1 4 9 9 3 0 ± 25 1 5 5 . 6 1 . 0 172 + 18 P 4 0 . 81 1 . 2 9 N 0 . 61 4 3 0 29 + 8 4 8 34 1 1 ± 1 4 1 156 0 0 . 6 35 + 8 E 2 0 . 19 0 2 3 N 0 . 0 4 3 0 53 + 2 4 6 16 14 ± 8 3 157 7 - 0 . 9 31 + 7 P 4 0 . 5 5 0 8 3 N 0 . 7 8 4 31 24 + 2 47 46 3 ± 8 5 156 7 0 . 2 33 + 5 P 3 0 18 0 23 N 0 . 4 9 4 31 32 + 2 4 6 13 27 ± 73 157 8 - 0 8 28 + 5 P 2 0 1 1 0 19 N 0 0 4 3 2 48 + 1 47 12 16 ± 6 0 157 3 - 0 0 73 + 9 P 6 0 81 1 4 5 N 0 10 4 3 3 15 + 8 4 8 2 0 27 ± 6 0 156 5 0 8 16 + 4 P 6 0 5 7 1 0 0 N 0 0 4 3 3 3 0 + 3 4 8 5 0 4 8 ± 44 156 1 1 2 29 + 4 P 6 0 6 8 1 25 N 0 0 4 3 3 4 0 + 1 4 8 11 3 9 ± 47 156 6 0 8 29 + 4 P 6 0 57 0 9 9 N 0 0 4 3 3 4 6 + 3 4 7 44 47 ± 43 157 0 0 5 41 + 7 P 4 0 3 5 0 7 0 N 0 7 0 4 34 21 + 1 4 8 4 5 7 ± 26 156 8 0 8 8 9 + 10 2 4 0 27 0 47 N 2 5 3 4 3 5 5 + 2 4 6 57 5 8 ± 6 6 157 7 0 1 28 + 4 P 4 0 8 7 1 4 7 N 0 0 4 3 5 7 + 2 4 8 16 17 ± 72 156 7 1 0 41 + 6 2 6 0 6 7 1 0 3 N 1 0 5 4 3 5 56 + 1 46 24 24 ± 5 9 158 2 - 0 1 34 + 5 E 6 0 9 0 1 4 0 N 0 7 0 4 3 6 56 + 2 44 25 16 ± 1 6 7 159 8 -1 3 25 + 4 P 5 0 6 9 0 9 6 N 0 0 4 3 8 0 + 4 4 6 1 17 ± 43 158 7 - 0 1 36 + 6 P 6 0 8 0 1 5 0 N 0 0 9 4 38 17 + 5 4 8 3 0 7 ± 28 156 9 1 6 9 6 + 10 P 4 0 2 9 0 4 5 N 0 0 4 3 8 35 + 2 4 5 28 14 ± 9 9 159 2 - 0 4 19 + 4 P 3 0 36 0 5 6 N 0 0 4 38 42 + 3 4 7 31 51 + 198 157 7 1 0 33 + 5 P 6 0 91 1 81 N 0 0 9 4 3 9 35 ± 1 4 8 16 4 9 + 28 157 2 1 6 102 + 9 P 2 0 3 9 0 4 2 N 0 0 4 3 9 56 + 1 4 7 27 37 ± 46 157 9 1 1 38 + 5 P 6 0 8 2 1 41 N 0 5 3 4 4 0 53 + 2 4 5 25 5 3 ± 4 9 159 5 - 0 1 38 + 5 E 6 0 7 3 1 2 0 N 1 0 1 4 41 5 + 3 4 6 38 1 ± 39 158 6 0 7 6 9 + 9 P 4 1 0 6 1 8 3 N 0 3 3 4 41 16 + 1 4 3 53 5 8 ± 28 1 6 0 7 -1 1 141 + 15 P 5 1 3 7 1 7 0 N 0 31 4 41 35 + 8 44 54 5 2 ± 54 160 . 0 - 0 4 34 + 8 P 4 0 8 6 1 3 3 N 0 31 4 4 3 10 + 2 44 18 5 ± 5 9 160 . 6 - 0 6 26 + 5 P 4 0 81 0 9 5 N 0 0 4 4 3 53 + 2 4 5 59 2 9 ± 81 159 . 4 0 6 25 + 5 E 4 0 . 16 0 . 2 4 N 1 22 4 4 5 4 9 + 8 4 5 34 4 9 ± 1 1 9 160 . 0 0 . 6 62 + 14 P 4 0 . 4 3 0 . 5 7 N 0 . 8 9 4 4 5 5 0 + 1 4 3 4 0 22 + 35 161 .4 - 0 . 6 119 + 14 P 6 1 . 34 2 . 4 9 N 0 . 5 3 4 4 6 0 + 1 44 3 9 ± 76 161 . 1 - 0 . 4 53 + 6 P 2 0 . 6 6 0 . 6 7 N 0 . 0 4 4 6 47 + 2 4 3 1 1 22 + 131 161 . 9 - 0 . 8 19 + 4 P 4 0 . 8 9 1 . 3 8 N 0 . 0 4 54 13 + 2 44 3 0 5 9 ± 47 161 . 7 1 . 1 31 + 4 P 4 1 . 0 6 1 . 5 9 N 0 . 0 4 5 5 28 + 2 42 4 5 2 + 47 163 . 8 - 0 . 3 49 + 10 P 4 0 . 4 2 0 . 5 6 N 1 . 9 4 4 5 5 54 + 2 4 3 7 13 ± 9 0 163 . 0 0 . 4 28 + 6 P 3 1 . 3 2 1 . 8 0 N 1 . 2 6 4 5 6 46 + 2 41 13 1 1 ± 7 0 164 . 6 - 0 . 6 23 + 6 P 3 1 . 14 1 . 4 4 N 0 . 4 6 4 5 6 5 0 + 7 41 58 3 6 ± 6 6 164 . 0 - 0 . 1 33 + 9 P 3 0 . 34 0 . 4 8 N 0 . 5 0 V a r 1 a t I o n s S h o r t T e r m N o . V i V I VAR? L o n g T e r m I n d e x VAR? N N N Y N N N N N N N N N N N N N N N N N N N N N N O t h e r C a t a l o g u e s 4C 5 0 . 1 2 0 F + 4 5 1 O F + 4 6 9 T a b l e V I . C o n t i n u e d NAME R A ( 1 9 5 0 ) h m s D E C ( 1 9 5 0 ) • r H 1 b F l u x D e n s i t y ( m J y ) D i a m N o . S h o r t V i V a r i a t i o n s T e r m V, V A R 7 L o n g I n d e x T e r m V A R 7 O t h e r C a t a l o g u e s G T 0 4 5 7 + 4 0 7 4 57 18 + 2 4 0 47 5 6 + 104 165 0 - 0 . 8 26 + 6 E 5 0 4 3 0 6 0 N 0 8 2 N G T 0 4 5 7 + 3 9 7 4 5 7 42 + 2 3 9 44 7 + 62 165 9 -1 . 4 48 + 8 P 3 1. 0 8 1 . 3 0 N 3 3 2 P G T 0 4 5 8 + 4 2 0 4 5 8 2 0 + 2 42 1 37 + 78 164 1 0 . 1 2 0 + 4 P 4 0 18 0 . 41 N 0 0 -G T 0 4 5 8 + 4 1 4 4 5 8 27 + 2 41 24 41 + 75 164 6 - 0 3 25 + 4 P 3 0 2 0 0 3 8 N 0 0 -G T 0 4 5 9 + 4 1 5 4 5 9 6 + 1 41 34 57 + 26 164 6 - 0 1 2 7 0 + 28 P 3 2 31 3 0 0 Y 4 3 9 Y G T 0 4 5 9 + 4 2 0 4 5 9 8 + 3 42 3 29 + 5 9 164 2 0 2 19 + 4 P 3 0 0 6 0 1 1 N 0 0 -G T 0 4 5 9 + 4 2 3 4 5 9 51 + 2 42 23 5 0 ± 77 164 0 0 6 82 + 13 P 4 0 6 1 0 8 4 N 0 7 6 N G T 0 5 0 0 + 4 1 5 5 0 7 + 2 41 3 5 21 ± 1 1 2 164 7 0 1 22 + 3 E 4 0 23 0 3 9 N 0 0 - 0 5 0 1 + 4 0 G T 0 5 0 1 + 4 0 9 5 1 54 + 8 4 0 54 4 + 61 165 4 - 0 1 78 + 13 2 3 0 74 1 0 2 N 0 8 7 N MW G T 0 5 0 1 + 3 9 2 5 1 5 6 + 2 3 9 12 32 + 6 5 . 166 8 -1 1 13 + 3 P 4 0 5 9 0 8 7 N 0 0 - 3 0 5 0 2 + 4 0 G T 0 5 0 2 + 4 0 2 5 2 51 + 2 4 0 15 31 ± 1 1 7 166 1 - 0 3 15 + 3 E 5 0 5 0 0 8 8 N 0 0 - B 2 G T 0 5 0 3 + 4 2 3 5 3 19 + 2 4 2 19 2 0 ± 1 9 8 164 5 1 0 36 + 8 E 4 O 16 0 3 9 N 0 8 6 N G T 0 5 0 4 + 4 1 2 5 4 28 + 1 41 12 44 ± 48 165 5 0 5 48 + 6 P 3 0 37 0 6 3 N 0 78 N G T 0 5 0 6 + 3 9 8 5 6 22 + 1 3 9 48 3 0 + 53 166 8 - 0 0 115 ± 13 P 3 0 7 9 0 9 8 N 1 9 9 N G T 0 5 0 6 + 3 8 1 5 6 36 + 1 38 10 5 8 + 79 168 2 -1 0 39 ± 6 E 5 1 0 4 1 5 8 N 1 3 6 N 3 0 5 0 7 + 3 7 G T 0 5 0 7 + 3 7 9 5 7 33 + 1 3 7 5 5 37 + 2 0 168 5 -1 0 5 3 7 ± 5 3 2 5 1 4 6 1 8 5 N 3 2 3 P B 2 G T 0 5 0 7 + 3 8 9 5 7 34 + 2 38 5 5 13 ± 1 2 6 167 7 - 0 4 23 ± 6 P 2 0 81 0 91 N 0 0 ~ G T 0 5 0 8 + 3 8 1 5 8 4 5 + 3 38 6 3 9 + 75 168 5 - 0 7 3 9 ± 8 P 2 0 0 3 0 0 9 N 0 0 - 0 5 0 9 + 4 0 G T 0 5 0 9 + 4 0 6 5 9 26 + 1 4 0 38 14 + 2 0 166 5 0 9 8 2 3 ± 8 2 P 3 1 19 1 6 5 N 1 27 N MW G T 0 5 1 0 + 4 0 0 5 10 17 + 1 4 0 3 2 6 + 34 167 1 0 7 158 + 18 1 5 1 32 2 34 N 0 28 N B 2 3 0 5 1 0 + 4 0 G T 0 5 1 0 + 3 8 7 5 10 3 0 + 1 3 8 42 3 6 + 24 168 2 - 0 0 2 0 0 + 21 P 4 1 12 1 5 2 N 1 8 8 N 4C 3 8 . 16 G T 0 5 1 0 + 4 0 3 5 10 35 + 8 4 0 22 2 0 + 5 3 166 9 0 9 4 1 5 + 55 2 4 0 9 3 1 3 5 N 1 9 5 N 3 0 5 1 0 + 3 8 B G T 0 5 1 0 + 3 8 4 5 10 58 + 1 38 27 28 + 5 9 168 4 - 0 1 32 + 3 E 5 0 8 3 1 0 5 N 0 0 - B 2 G T 0 5 1 1 + 3 9 7 5 1 1 22 + 1 3 9 44 4 6 ± 61 167 4 0 7 4 3 + 7 P 3 0 7 6 0 9 8 N 2 26 N B 2 3 0 5 1 1 + 3 9 G T 0 5 1 2 + 3 7 8 5 12 25 + 8 37 52 41 + 4 3 . 169 1 - 0 2 5 5 2 + 73 P 2 1 41 1 4 7 N 0 0 - 4C 3 7 . 13 G T 0 5 1 3 + 3 8 6 5 13 8 + 2 38 3 8 0 + 81 168 5 0 3 18 + 3 E 4 0 77 1 14 N 0 0 - 3 0 5 1 3 + 3 6 G T 0 5 1 3 + 3 6 1 5 13 41 + 4 3 6 9 5 9 + 51 170 6 - 1 0 4 6 + 9 P 2 0 3 3 0 4 7 N 0 0 - B 2 G T 0 5 1 3 + 3 9 9 5 13 4 9 + 2 3 9 5 8 34 + 8 0 167 5 1 2 29 + 6 . P 2 0 54 0 6 3 N 0 0 -G T 0 5 1 4 + 3 7 4 5 14 18 + 2 37 24 56 + 47 169 7 - 0 2 2 0 + 3 P 3 0 71 0 9 0 N 0 0 G T 0 5 1 4 + 3 9 1 . 5 14 35 + 3 3 9 7 28 ± 1 2 3 168 3 0 8 43 + 7 P 4 0 4 9 0 61 N 0 4 5 N G T 0 5 1 5 + 3 8 9 5 15 0 + 2 3 8 5 5 5 2 + 6 7 168 5 0 8 14 + 3 P 3 0 6 3 0 8 0 N 0 0 ~ G T 0 5 1 6 + 3 7 6 5 16 12 + 4 37 38 4 6 ± 1 9 8 169 7 0 2 3 0 + 6 P 4 0 32 0 5 6 N 0 6 7 N G T 0 5 1 6 + 3 6 1 5 16 13 + 2 3 6 1 1 3 0 + 7 8 170 9 - 0 6 14 + 3 P 4 0 5 8 0 8 2 N 0 0 G T 0 5 1 6 + 3 7 0 5 16 2 9 1 37 3 15 + 71 170 2 - 0 1 31 + 5 P 4 0 8 5 1 44 N 0 0 -G T 0 5 1 6 + 3 8 1 5 16 38 + 2 3 8 8 3 + 76 169 4 0 6 22 + 3 P 3 0 17 0 19 N 0 0 -G T 0 5 1 7 + 3 5 3 5 17 18 + 2 35 2 0 36 + 5 7 171 7 - 0 9 24 + 4 E 4 0 47 0 57 N 0 0 - 3 0 5 1 7 + 3 6 G T 0 5 1 7 + 3 6 1 5 17 2 0 + 1 36 8 1 + 29 171 .1 - 0 4 118 + 13 P 4 0 57 0 7 6 N 2 36 N B 2 G T 0 5 1 8 + 3 7 5 5 18 31 + 2 37 32 15 + 6 6 170 1 0 6 18 + 4 P 3 0 8 0 1 0 1 N 0 0 G T 0 5 1 8 + 3 8 1 5 18 53 + 2 38 7 1 + 5 9 169 6 0 9 2 0 + 4 P 3 0 4 9 0 6 2 N 0 0 - 3 0 5 1 9 + 3 6 A G T 0 5 1 9 + 3 6 0 5 19 5 • 3 3 6 3 37 + 47 171 3 - 0 2 4 2 + 7 P 4 0 8 0 0 9 3 N 0 2 8 N B 2 G T 0 5 2 1 + 3 7 5 5 21 5 + 2 37 35 39 + 76 170 3 1 6 24 + 5 P 3 0 7 3 1 0 3 N 0 0 -G T 0 5 2 1 + 3 6 1 5 21 9 + 2 36 8 5 8 + 71 171 5 0 2 14 + 3 P 5 0 71 0 94 N 0 0 - 3 0 5 2 1 + 3 6 G T 0 5 2 1 + 3 6 4 5 21 23 + 2 36 24 37 + 73 171 3 0 4 28 + 5 P 4 0 3 5 0 4 8 N 1 0 9 N B 2 T a b l e V I . C o n t i n u e d NAME R A ( 1 9 5 0 ) h m s D E C ( 1 9 5 0 ) F l u x D e n s i t y ( m o y ) D i a m N o . V a r l a t I o n s S h o r t T e r m V i V I V A R ? L o n g T e r m I n d e x V A R ? O t h e r C a t a l o g u e s G T 0 5 2 1 + 3 4 1 G T 0 5 3 3 + 3 0 1 G T 0 5 3 4 + 3 1 3 G T 0 5 3 4 + 3 3 0 G T 0 5 3 4 + 3 0 9 G T 0 5 3 5 + 3 1 8 G T 0 5 3 5 + 3 1 4 G T 0 5 3 5 + 3 3 1 G T 0 5 3 G + 3 1 6 G T 0 5 3 7 + 3 1 0 G T 0 5 3 8 + 2 8 6 G T 0 5 3 8 + 3 0 7 G T 0 5 3 9 + 2 9 0 G T 0 5 3 9 + 2 8 4 G T 0 5 4 0 + 3 1 6 G T 0 5 4 0 + 2 8 2 G T 0 5 4 2 + 2 9 8 G T 0 5 4 2 + 2 9 1 G T 0 5 4 4 + 2 7 3 G T 0 5 4 5 + 2 7 2 G T 0 5 4 5 + 2 9 7 G T 0 5 4 5 + 2 5 8 G T 0 5 4 5 + 2 6 5 G T 0 5 4 5 + 2 6 2 G T 0 5 4 5 + 2 8 4 G T 0 5 4 5 + 2 7 6 G T 0 5 4 6 + 2 7 8 G T 0 5 4 6 + 2 8 2 G T 0 5 4 7 + 2 7 7 G T 0 5 4 7 + 2 8 1 G T 0 5 4 8 + 2 6 7 G T 0 5 4 8 + 2 5 8 G T 0 5 4 8 + 2 5 9 G T 0 5 4 8 + 2 7 0 G T 0 5 5 0 + 2 7 0 G T 0 5 5 1 + 2 6 3 G T 0 5 5 1 + 2 7 1 G T 0 5 5 2 + 2 6 6 G T 0 5 5 3 + 2 5 4 G T 0 5 5 3 + 2 6 1 G T 0 5 5 4 + 2 4 2 G T 0 5 5 5 + 2 3 0 G T 0 5 5 5 + 2 2 6 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 21 3 3 34 34 34 3 5 3 5 3 5 3 6 37 3 8 3 8 3 9 3 9 4 0 4 0 42 4 2 44 4 5 4 5 4 5 4 5 4 5 4 5 4 5 4 6 4 6 4 7 4 7 4 8 4 8 4 8 4 8 5 0 51 51 5 2 5 3 5 3 54 5 5 5 5 43 44 15 37 55 21 33 5 3 4 5 5 0 5 17 1 5 9 6 21 52 54 26 18 3 0 31 32 49 4 9 57 34 44 4 0 4 3 4 15 35 41 42 18 37 5 9 15 16 3 4 31 34 8 3 0 8 31 18 33 3 3 0 5 5 31 5 3 31 2 6 3 3 6 31 3 8 31 0 28 41 3 0 4 5 29 0 28 24 31 37 2 8 14 29 4 8 2 9 7 27 2 0 27 16 29 4 5 25 5 0 26 34 2 6 13 2 8 2 5 27 36 27 51 2 8 17 27 4 3 2 8 1 1 26 44 2 5 4 8 2 5 57 27 1 21 17 2 47 18 4 0 9 5 31 17 15 10 28 1 5 8 12 52 4 6 4 3 1 2 5 2 0 2 6 22 15 5 5 5 47 + 74 + 51 + 105 ± 81 4 6 94 52 24 6 7 72 28 47 21 ± 1 8 7 + 42 ± 1 9 8 27 2 6 27 0 18 6 + + + + + + + + + + + + 16 ± 1 0 6 18 ± 1 8 4 ± 42 + 41 ± 26 ± 23 5 3 ± 1 9 8 5 3 ± 1 4 6 9 5 5 6 21 5 0 8 9 4 9 24 5 3 6 3 21 3 5 8 5 2 0 15 2 0 23 26 38 2 5 27 2 6 10 24 13 2 3 2 22 37 10 7 5 2 22 15 2 9 11 6 0 5 9 8 9 22 22 71 38 . 0 . 7 . 7 . 2 . 4 . 3 . 3 . 9 . 6 1 7 3 . 2 178 . 0 177 . 0 1 7 5 . 6 1 7 7 . 4 1 7 6 . 7 177 . 1 1 7 5 . 7 177 177 179 1 7 8 . 0 1 7 9 . 5 180 177 180 179 179 181 1 8 1 . 7 1 7 9 . 6 1 8 3 . 0 1 8 2 . 4 1 8 2 . 7 1 8 0 . 8 1 8 1 . 5 181 . 4 181 . 0 1 8 1 . 6 1 8 1 . 2 1 8 2 . 5 183 183 182 182 183 182 183 184 183 185 186 186 - 0 . 9 - 1 . 0 - 0 . 2 0 . 8 0 . 3 - 0 . 9 0 . 5 0 . 2 - 0 . 4 - 0 . 3 1 . 0 - 1 . 0 - 0 . 6 0 . 4 0 . 6 21 2 0 2 2 23 2 5 2 5 5 8 140 27 44 4 8 2 1 13 4 4 6 3 3 6 7 4 1 29 6 4 4 5 3 3 8 19 9 3 196 4 6 37 3 0 4 177 2 6 41 6 0 1 13 5 6 2 6 2 3 2 5 3 2 23 27 31 18 194 9 4 9 4 8 1 0 0 + + + + + + + + + + + + + + + + + + + + + + + + + + + + • + + + + + + + + + + + +. 7 ± 1 1 3 3 3 3 5 5 7 15 4 10 4 9 23 4 5 7 10 9 6 9 4 6 6 5 18 2 0 8 9 3 0 19 6 8 7 14 9 31 33 7 4 5 5 4 2 0 94 P P P P P E E P E P 2 P P P P E P P P P P P P P P P P P P P 2 P P 4 E P P P P P P P P 4 4 4 4 2 3 2 3 3 3 1 1 4 3 4 1 3 4 3 4 3 1 3 1 1 3 1 1 1 4 1 3 3 3 3 4 4 4 2 4 4 1 2 0 . 5 9 0 . 5 9 0 . 2 1 0 . 4 0 0 . 7 7 0 . 4 8 0 . 0 9 0 . 3 6 0 . 2 8 0 . 14 1 .11 0 . 3 3 0 . 5 9 1 . 0 0 0 . 8 3 0 . 4 0 0 . 6 0 0 . 2 7 0 . 3 9 0 . 7 3 0 . 6 5 0 . 9 6 0 . 3 8 0 . 4 6 0 . 4 0 0 . 4 6 0 . 7 5 2 . 5 6 9 7 74 37 54 7 9 6 2 0 . 12 0 . 6 1 0 . 4 3 0 . 2 5 2 . 0 0 0 . 4 4 0 . 8 1 1 . 3 3 1 .11 0 . 5 2 0 . 9 4 0 . 3 8 0 . 5 9 1 . 0 7 0 . 8 6 1 . 3 3 0 . 6 9 0 . 8 4 0 . 6 9 0 . 5 0 1 . 3 2 3 . 15 N N N N N N N N N N 1 . 1 8 1 . 5 9 N 1 . 4 8 2 . 0 3 N 0 . 4 0 0 . 6 8 N N N N N N N N N N Y 0 . 1 4 0 . 2 1 N 0 . 0 0 . 0 0 . 0 0 . 0 0 . 0 0 . 9 3 0 . 0 1 .61 0 . 0 0 . 8 2 0 . 0 0 . 7 4 0 . 4 8 0 . 0 1. 18 0 . 0 1 . 18 0 . 0 5 . 4 1 0 . 0 0 . 0 0 . 3 4 1 . 3 9 0 . 4 5 . 0 . 5 5 . 5 1 . 4 2 0 . 0 2 . 9 0 0 . 0 0 . 6 9 0 . 13 0 . 3 7 0 . 6 6 0 . 0 1 . 4 0 0 . 0 0 . 0 1 . 0 9 6 . 0 8 0 . 0 1 . 4 3 0 . 0 . 2 . 1 N N N N N N N N N N N Y O G + 3 5 9 B 2 0 5 3 5 + 3 1 GC 0 5 3 5 + 3 3 B 2 0 5 3 6 + 3 1 B 2 0 5 3 7 + 3 1 4C 2 8 . 16 B 2 0 5 3 8 + 3 0 4 C 2 9 . 1 9 B 2 0 5 4 0 + 3 1 B 2 0 5 4 2 + 2 9 B 2 . 2 0 5 4 2 + 2 9 B 2 . 2 0 5 4 4 + 2 7 4C 2 6 . 18 B 2 . 2 0 5 4 6 + 2 8 B 2 . 2 0 5 4 7 + 2 7 B 2 . 2 0 5 4 8 + 2 5 A B 2 . 2 0 5 4 8 + 2 5 B AO 0 5 4 8 + 2 7 B 2 . 2 0 5 5 3 + 2 6 A B 2 . 4 0 5 5 5 + 2 2 T a b l e V I . C o n t i n u e d NAME R A ( 1 9 5 0 ) h m s D E C ( 1 9 5 0 ) * / If 1 b F l u x D e n s i t y ( m J y ) D l a m N o . S h o r t Vi V a r i a t i o n s T e r m Vi V A R ? L o n g I n d e x T e r m V A R ? O t h e r C a t a l o g u e s G T 0 5 5 6 + 2 3 8 5 5 6 36 + 2 2 3 53 9 ± 31 185 9 0 1 122 + 14 P 4 1 24 1 4 9 N 0 0 -G T 0 5 5 9 + 2 2 9 5 5 9 0 + 2 22 5 8 2 ± 8 6 187 0 0 2 48 + 9 P 1 - - - 0 0 -G T 0 5 5 9 + 2 3 4 5 5 9 1 + 2 2 3 25 4 0 + 132 186 6 0 4 21 + 4 P 4 0 2 9 0 37 N 0 0 N G T 0 5 5 9 + 2 2 5 5 5 9 24 + 1 2 2 34 4 9 + 62 187 4 0 0 3 0 + 5 P 4 0 54 0 9 7 N 0 0 -G T 0 5 5 9 + 2 1 4 5 5 9 39 + 2 21 29 5 7 ± 6 6 188 4 - 0 4 32 + 6 P 1 - - - 0 0 -G T 0 6 0 0 + 2 0 7 6 0 3 9 + 1 2 0 47 4 6 ± 33 189 1 - 0 6 76 + 10 P 3 0 8 7 1 34 N 0 0 - OH+201 G T 0 6 0 1 + 2 0 3 6 1 8 + 2 2 0 21 4 6 ± 76 189 5 - 0 7 6 5 + 13 P 1 - - - 0 7 8 N G T 0 6 0 1 + 2 1 9 6 1 28 + 2 21 58 4 2 + 6 6 188 2 0 2 22 + 4 P 2 0 0 4 0 0 6 N 0 0 -G T 0 6 0 2 + 2 1 0 6 2 26 + 2 21 3 3 + 107 189 1 - 0 1 21 + 5 P 3 0 42 0 6 3 N 0 o -G T 0 6 0 3 + 2 1 8 6 3 13 + 2 21 49 5 9 + 6 2 188 5 0 4 6 2 + 12 P 1 - - - 0 0 - B 2 . 4 0 6 0 3 + 2 1 G T 0 6 0 3 + 2 2 5 6 3 37 + 2 22 31 41 + 123 187 9 0 9 22 + 6 E 1 - - - 0 0 -G T 0 6 0 3 + 2 1 9 6 3 37 + 2 21 59 35 ± 71 188 4 0 6 28 + 5 P 2 0 2 0 0 2 9 N 0 0 -G T 0 6 0 4 + 2 1 7 6 4 2 ± 2 21 44 32 ± 81 188 7 0 6 35 + 6 P 1 - - - 0 0 -G T 0 6 0 5 + 2 1 6 6 5 5 + 2 21 36 7 ± 1 2 2 188 9 0 7 34 + 8 P 1 - - - 0 0 -G T 0 6 0 5 + 2 0 6 6 5 29 + 1 2 0 39 42 ± 32 189 8 0 3 173 + 18 2 1 - - - 0 9 9 N G T O S 0 5 + 1 8 4 6 5 5 6 + 2 18 28 14 ± 48 191 7 - 0 7 37 ± 8 P 1 - - - 0 0 -G T 0 6 0 6 + 1 9 3 6 6 5 3 + 2 19 18 3 0 + 78 191 1 - 0 1 22 + 4 P 4 0 6 6 0 9 3 N 0 0 -G T 0 6 0 6 + 1 7 4 6 6 57 + 1 17 26 18 ± 39 192 7 -1 0 97 + 12 3 4 0 8 6 1 44 N 0 0 - 0 H + 1 1 2 G T 0 6 0 7 + 1 7 0 6 7 16 + 4 17 1 9 ± 1 5 6 193 1 - 1 1 38 + 10 E 1 - - - 0 0 -G T 0 6 0 7 + 1 8 3 6 7 5 0 + 8 18 18 52 + 198 192 1 - 0 3 . 47 + 12 P 1 - - - 0 0 -G T 0 6 1 0 + 1 9 6 6 10 9 + 2 19 38 4 9 ± 1 9 8 191 2 0 8 27 + r 5 P 3 0 76 0 9 7 N 0 0 -G T 0 6 1 0 + 1 7 9 6 10 13 + 1 17 5 9 4 8 ± 25 192 6 - 0 0 9 5 5 ± 9 5 2 1 - - - 1 5 5 N 0 C C 1 9 2 . 6 - O O . 0 G T 0 6 1 0 + 1 8 5 6 10 25 + 2 18 35 2 3 ± 9 7 192 1 0 3 4 3 + 9 E 1 - - - 0 0 -G T 0 6 1 0 + 1 6 5 6 10 4 0 + 1 16 33 7 ± 4 7 194 0 - 0 6 47 + 5 P 3 0 6 4 0 9 3 N 0 0 -G T 0 6 1 0 + 1 7 1 6 10 41 + 1 17 9 3 8 ± 38 193 4 - 0 3 166 + 18 1 1 - • - - 1 4 8 N G T 0 6 1 3 + 1 7 0 6 13 7 + 2 17 0 3 0 + 54 193 8 0 1 36 + 7 P 1 - - - 0 0 -G T 0 6 1 4 + 1 6 7 6 14 27 + 1 16 44 58 ± 4 3 194 2 0 3 9 2 + 10 2 2 0 19 0 2 0 N 1 6 5 N 4 C 1 6 . 1 6 G T 0 6 1 7 + 1 4 9 6 17 0 + 8 14 5 5 51 ± 1 0 5 196 1 - 0 0 148 + 26 P 2 1 41 1 9 7 . N 0 0 -G T 0 6 1 7 + 1 3 5 6 17 12 + 1 13 32 5 5 ± 5 0 197 3 - 0 7 7 0 + 8 2 3 0 42 0 5 2 N 0 0 -G T 0 6 1 7 + 1 3 8 6 17 3 0 + 2 13 4 8 5 ± 6 6 197 2 - 0 5 72 + 12 P 2 0 21 0 3 0 N 0 4 2 N 0 H + 1 2 9 G T 0 6 1 8 + 1 4 0 6 18 35 + 2 14 0 1 + 73 197 1 - 0 2 35 + 7 P 1 - - - 0 0 -G T 0 6 1 8 + 1 5 4 6 18 42 + 5 15 29 32 ± 1 4 0 195 8 0 6 28 + 6 E 4 1 4 9 2 5 3 N 0 0 -G T 0 6 1 8 + 1 4 5 6 18 4 9 + 1 14 33 18 + 2 0 196 6 0 2 722 + 55 P 1 - - - 0 0 - 3C 158 G T 0 6 2 0 + 1 4 2 6 2 0 12 + 1 14 15 5 9 ± 6 8 197 1 0 3 64 + 8 P 2 0 4 0 0 5 6 N 0 0 -G T 0 6 2 0 + 1 5 8 6 2 0 2 0 + 6 15 4 9 22 ± 1 10 .195 7 1 1 52 + 13 P 3 0 9 0 1 2 3 N 1 11 N G T 0 6 2 1 + 1 4 4 6 21 41 + 3 14 28 3 0 + 61 197 0 0 7 28 + 7 P 3 0 8 2 1 21 N 0 0 -G T 0 6 2 2 + 1 3 2 6 22 16 + 2 13 14 5 ± 1 4 2 198 2 0 3 47 + 9 E 1 - - - 0 0 -G T 0 6 2 2 + 1 1 8 6 22 28 + 1 1 1 51 25 ± 58 199 4 - 0 3 42 + 7 P 3 0 5 6 0 8 3 N 0 0 -G T 0 6 2 2 + 1 0 9 6 2 2 3 9 + 1 10 55 42 ± 26 2 0 0 3 - 0 7 2 6 6 + 28 3 1 - - - 11 24 Y G T 0 6 2 5 + 1 2 0 6 2 5 5 + 2 12 1 3 8 ± 1 0 2 199 6 0 3 4 2 + 9 E 1 - - - 0 0 -G T 0 6 2 5 + 1 2 8 6 2 5 3 0 • 2 12 4 9 2 + 100 198 9 0 8 5 0 + 8 E 3 0 19 0 21 N 0 0 8 N G T 0 6 2 6 + 1 1 9 6 2 6 24 + 3 1 1 58 51 + 198 199 8 0 6 23 + 5 P 4 1 2 0 1 8 5 N 0 0 -G T 0 6 2 8 + 1 0 9 6 2 8 6 + 1 10 58 33 ± 34 2 0 0 9 0 5 146 + 16 P 2 0 0 1 0 16 • N 0 7 2 N 4C 1 0 . 1 9 T a b l e V I . C o n t i n u e d NAME R A ( 1 9 5 0 ) h m s D E C ( 1 9 5 0 ) 1 b F l u x D e n s i t y ( m J y ) 01 am N o . S h o r t V i V a r l a t I o n s T e r m V i VAR? L o n g I n d e x T e r m VAR? O t h e r C a t a l o g u e s G T 0 6 2 8 + 0 9 9 6 2 8 19 + 3 9 5 9 51 + 61 201 . 8 0 . 1 5 0 + 12 P 1 - - - 0 . 0 - 4 C P 0 8 . 21 G T O 6 3 0 + O 8 2 6 3 0 26 + 1 8 15 9 + 34 2 0 3 5 - 0 . 3 2 6 2 + 27 2 4 1. 7 9 2 . 8 0 P 0 . 0 G T 0 6 3 0 + 1 0 8 6 3 0 34 + 2 10 5 2 4 9 + 5 9 201 . 2 1 . b 38 + 5 E 4 0 . 23 0 . 3 5 N 0 . 0 N 4 C P 0 9 . 2 4 G T 0 6 3 1 + 0 9 7 6 31 1 + 1 9 4 5 7 + 43 2 0 2 3 0 . 5 122 + 14 P 4 0 . 6 2 1 . 10 N 0 5 6 G T 0 6 3 1 + 1 0 7 6 31 31 + 2 10 4 6 8 + 5 6 201 4 1 . 1 34 + 8 P 1 - ~ ~ 0 O " G T 0 6 3 1 + 0 9 0 6 31 43 + 4 9 5 3 6 + 9 2 2 0 2 9 0 . 4 64 + 15 P 2 0 . 7 9 0 . 9 0 N 0 0 N G T 0 6 3 2 + 1 0 3 6 32 22 + 2 10 21 5 6 + 61 201 9 1 . 1 4 5 + 7 P 2 0 . 2 0 0 . 26 N 1 32 N G T O G 3 2 + 0 9 5 6 3 2 22 + 2 9 34 16 + 78 2 0 2 6 0 . 7 4 6 + 10 P 1 " ~ 0 0 G T 0 6 3 3 + 0 7 0 6 3 3 12 + 2 7 0 0 + 6 8 2 0 5 0 - 0 3 4 6 + 6 E 3 0 . 71 1 . 0 9 N 0 0 N G T 0 6 3 3 + 0 8 0 6 3 3 56 + 1 8 4 2 3 + 4 3 204 1 0 . 4 211 + 23 P 1 - ~ ~ 0 8 9 G T 0 6 3 4 + 0 5 6 6 34 52 + 5 5 38 2 ± 1 9 8 2 0 6 4 - 0 5 3 9 + 10 E 3 0 . 12 0 24 N 0 0 G T 0 6 4 5 + 0 1 8 6 4 5 38 + 2 1 4 9 1 1 + 8 6 211 0 0 1 61 + 1 1 P 3 0 . 64 1. 12 N 1 4 2 N G T 0 6 4 6 + 0 0 2 6 4 6 38 + 1 0 12 12 ± 1 9 1 2 1 2 5 - 0 4 9 3 + 15 P 1 - 0 0 G T 0 6 4 6 - 0 0 2 6 4 6 45 + 4 - 0 13 24 ± 1 6 1 2 1 2 5 - 0 4 7 0 + 18 P 1 - 0 0 N G T 0 6 4 8 + 0 1 5 6 4 8 15 + 4 1 3 3 18 ± 1 7 2 211 5 0 5 26 + 8 P 4 0 17 0 31 N 0 0 — G T 0 6 5 0 - 0 0 8 6 5 0 28 + 3 - 0 4 9 2 8 + 167 2 1 2 4 0 7 100 + 15 E 3 0 5 6 0 8 0 N 0 0 — 4 C - 0 2 . 2 9 G T 0 6 5 1 - 0 2 7 6 51 36 + 2 - 2 4 3 5 2 ± 1 3 4 2 1 0 9 1 8 9 7 + 11 E 2 1 0 3 1 15 N 0 0 G T O G 5 3 - 0 1 7 6 5 3 4 + 2 - 1 4 6 16 ± 1 0 8 211 9 1 7 2 8 + 6 P 4 0 9 2 1 2 9 N 0 0 G T 0 6 5 4 - 0 0 8 6 54 32 + 1 - 0 4 9 4 8 + 5 6 2 1 2 9 1 6 143 + 16 1 4 1 17 1 6 9 N 0 0 ~ G T 1 9 3 3 + 1 9 3 19 3 3 7 + 5 19 21 18 ± 9 3 5 5 2 - 0 4 6 5 ± 13 E 2 0 18 0 24 N 0 0 N G T 1 9 3 3 + 1 9 8 19 3 3 25 + 2 19 51 3 9 + 78 5 5 6 - 0 3 31 + 6 P 4 0 6 6 0 94 N 0 0 9 G T 1 9 3 3 + 2 0 2 19 3 3 57 + 1 2 0 16 15 + 7 0 56 1 - 0 2 1 17 + 14 P 6 1 0 5 1 91 N 1 5 9 N G T 1 9 3 4 + 2 1 5 19 34 17 + 2 21 3 5 4 8 + 81 57 3 0 4 2 0 + 3 P 4 0 35 0 4 9 N 0 0 — GT 1 9 3 5 + 2 1 1 19 3 5 14 + 8 21 6 3 8 + 9 9 5 6 9 - 0 0 54 + 16 P 19 0 74 1 7 8 N 1 8 2 N G T 1 9 3 5 + 2 2 7 19 3 5 57 + 8 22 4 2 17 + 100 5 8 4 0 6 4 8 + 10 1 19 0 91 2 2 9 N 0 0 G T 1 9 3 7 + 2 0 7 19 37 6 + 4 2 0 4 5 9 + 94 56 8 - 0 6 3 0 + 6 E 5 0 5 0 0 7 6 N 0 0 — P K S 1937+21 G T 1 9 3 7 + 2 1 5 19 37 33 + 1 21 3 0 0 + 21 57 5 - 0 3 5 7 7 + 57 2 5 1 64 2 8 3 P 1 77 N G T 1 9 3 8 + 2 1 5 19 3 8 35 + 2 21 33 24 ± 1 9 8 57 7 - 0 5 3 0 + 5 E 18 0 8 5 1 6 2 N 2 18 N G T 1 9 3 8 + 2 0 2 19 3 8 36 ± 1 2 0 16 13 + 9 6 5 6 6 -1 1 34 + 5 P 6 1 25 1 9 6 N 0 18 N G T 1 9 4 0 + 2 2 4 19 4 0 6 + 1 22 28 4 9 + 4 9 58 7 - 0 3 7 6 + 9 5 6 0 5 9 1 0 7 N 0 38 N B 2 . 4 1 9 4 0 + 2 3 G T 1 9 4 0 + 2 3 7 19 4 0 26 + 1 2 3 4 2 37 + 2 0 5 9 8 0 2 9 2 5 ± 9 2 1 5 0 5 9 0 8 0 N 1 31 N G T 1 9 4 0 + 2 4 9 19 4 0 4 0 + 3 24 5 9 4 6 + 8 9 6 0 9 0 8 34 + 9 E 3 0 0 0 0 N 1 4 9 N G T 1 9 4 1 + 2 5 0 19 41 28 + 1 2 5 1 7 + 3 0 61 . 0 0 7 77 + 9 P 6 0 32 0 5 6 N 2 8 3 N B 2 . 4 1943+22 G T 1 9 4 3 + 2 2 8 19 4 3 58 + 1 22 5 2 2 6 + 22 5 9 . 5 - 0 9 2 4 8 + 25 P 5 1 6 8 2 9 2 P 1 5 9 N G T 1 9 4 5 + 2 4 1 19 4 5 51 + 1 24 7 2 0 + 54 6 0 .8 - 0 6 8 9 + 9 P 19 1 19 3 52 Y 0 0 B 2 . 2 1945+24 G T 1 9 4 5 + 2 4 6 19 4 5 58 + 1 24 41 4 8 + 28 61 . 3 - 0 4 100 + 10 P 19 1 28 2 5 6 N 0 . 0 D C C 0 6 1 . 2 - 0 0 . 4 G T 1 9 4 7 + 2 6 7 19 4 7 6 + 1 2 6 4 3 2 3 + 25 6 3 . 2 0 5 1381 • 138 3 19 1 64 3 22 P 0 . 0 P K S 1 9 4 7 + 2 6 . 6 G T 1 9 4 8 + 2 8 1 19 4 8 32 + 1 28 9 54 + 54 64 . 6 0 9 21 + 2 5 19 0 9 2 2 13 N 0 . 0 N G T 1 9 5 2 + 2 7 7 19 5 2 1 + 1 27 44 18 + 9 5 64 . 6 0 0 4 6 + 8 E 19 0 6 9 1 . 3 5 N 2 . 9 5 G T 1 9 5 2 + 2 8 7 19 5 2 31 + 2 28 47 41 + 4 9 6 5 . 5 0 5 4 7 + 8 P 19 0 6 2 1 14 N 1 . 4 2 N B 2 . 2 1 9 5 3 + 2 8 GT 1 9 5 3 + 2 8 4 19 5 3 1 + 2 2 8 27 44 + 5 3 6 5 . 3 0 . 2 106 + 14 P 5 0 3 0 0 . 4 8 N 0 . 6 6 N G T 1 9 5 3 + 2 9 1 19 5 3 2 + 1 2 9 9 14 + 39 6 5 . 9 0 . 6 38 + 4 E 7 1 0 2 2 . 0 0 N 0 . 0 - . PK 0 6 5 + 0 0 .1 G T 1 9 5 3 + 2 7 1 19 5 3 29 + 1 27 9 4 + 92 64 . 3 - 0 . 5 44 + 7 P 5 0 74 1 . 2 8 N 2 . 19 N CD T a b l e V I . C o n t i n u e d NAME R A ( 1 9 5 0 ) h m s D E C ( 1 9 5 0 ) • * n 1 b F l u x D e n s i t y ( m J y ) D i a m N o . S h o r t V i V a r l a t I o n s T e r m V i V A R ? L o n g I n d e x T e r m V A R ? O t h e r C a t a l o g u e s GT 1953 + 2 7 5 19 5 3 29 + 8 27 3 0 54 + 61 64 . 6 - 0 . 3 41 + 8 E 5 1 . 4 5 2 . 6 3 N 0 . 0 _ GT 1 9 5 3 + 2 9 5 19 5 3 47 + 2 2 9 34 4 5 + 8 0 6 6 . 4 0 . 7 19 + 3 P 6 0 . 6 8 1 . 10 N 0 . 0 G T 1 9 5 3 + 3 0 6 19 5 3 4 8 + 1 3 0 36 1 ± 6 9 6 7 . 2 1 . 2 26 + 4 P 5 1 . 6 8 2 . 8 2 P 3 . 0 5 P G T 1 9 5 3 + 2 8 7 19 5 3 4 8 + 2 28 4 2 17 ± 9 8 6 5 . 6 0 . 2 24 + 5 P 2 0 . 0 2 0 . 0 5 N 0 . 0 _ G T 1 9 5 4 + 2 7 8 19 54 6 + 2 27 5 0 5 7 ± 1 9 8 64 . 9 - 0 . 3 18 + 4 P 5 0 . 7 4 1 . 2 4 N 1 . 0 5 N G T 1 9 5 4 + 2 6 7 19 54 7 + 1 2 6 4 7 5 ± 3 9 64 . 0 - 0 8 105 + 12 P 7 0 . 7 9 1 .11 N 0 . 0 N B 2 . 2 1 9 5 4 + 2 6 G T 1 9 5 4 + 2 7 1 19 54 33 + 8 27 8 19 ± 9 0 64 . 4 - 0 7 5 3 + 13 P 5 1 . 0 5 1 . 8 3 N O . O - B 2 . 2 1 9 5 4 + 2 7 G T 1 9 5 5 + 2 7 9 19 5 5 38 ± 2 27 5 8 3 0 ± 47 6 5 . 2 - 0 5 23 + 3 P 6 0 . 6 9 1 . 2 0 N 0 . 0 -G T 1 9 5 5 + 2 7 7 19 5 5 47 ± 1 27 4 2 13 ± 3 0 6 5 0 - 0 7 71 + 8 P 5 1 . 2 2 2 . 2 8 N 0 . 3 8 N B 2 . 2 1 9 5 5 + 2 7 A G T 1 9 5 6 + 2 8 3 19 5 6 3 0 ± 2 28 19 4 9 + 109 6 5 6 - 0 5 2 3 + 4 P 2 0 6 2 0 . 6 2 N 0 . 0 -G T 1 9 5 7 + 3 0 8 19 5 7 17 ± 1 3 0 5 0 9 ± 2 3 6 7 8 0 7 188 + 19 P 5 1 . 14 1 . 6 9 N 0 . 8 0 N B 2 1 9 5 7 + 3 0 G T 1 9 5 7 + 3 0 7 19 57 54 ± 1 3 0 42 5 9 ± 3 9 6 7 8 0 5 8 9 + 10 6 4 0 51 0 . 8 0 N 2 . 0 0 N G T 1 9 5 8 + 3 1 0 19 5 8 36 ± 3 31 1 4 5 ± 1 9 8 6 8 1 0 6 3 0 + 4 P 5 0 6 2 1 . 0 5 N 0 . 0 -G T 1 9 5 8 + 2 9 2 19 58 53 ± 2 29 13 3 5 ± 8 6 6 6 6 - 0 5 17 + 3 P 5 0 4 0 0 . 7 0 N 0 . 0 - B 2 2 1 9 5 8 + 2 9 G T 1 9 5 9 + 3 2 1 19 5 9 17 ± 1 32 8 34 ± 3 0 6 9 2 1 0 71 + 8 P 18 1 0 6 2 . 3 6 N 3 . 4 7 P G T 1 9 5 9 + 2 8 0 19 5 9 21 + 2 28 0 14 ± 5 0 6 5 7 -1 2 23 + 3 P 5 0 7 7 1 . 4 2 N 0 . 0 _ G T 1 9 5 9 + 3 1 2 19 5 9 47 + 1 31 13 21 ± 36 6 8 4 0 4 61 + 7 2 18 0 9 5 2 . 0 8 N 1 . 8 9 N G T 2 0 0 0 + 2 9 7 2 0 0 31 + 8 29 4 5 2 7 ± 5 5 6 7 3 - 0 5 64 + 13 P 18 1 28 2 . 19 N 2 . 4 5 N B 2 2 0 0 0 + 2 9 G T 2 0 O O + 2 9 2 2 0 0 42 + 4 2 9 13 8 ± 5 9 6 6 9 - 0 8 21 + 6 P 3 0 1 1 0 . 2 8 N 0 . 0 -G T 2 0 O 0 + 2 8 7 2 0 0 4 9 + 1 28 4 5 2 9 ± 1 8 7 6 6 5 -1 1 1 1 + 2 E 18 1 12 3 . 8 1 Y 2 . 4 3 N G T 2 0 0 1 + 3 0 9 2 0 1 47 + 8 3 0 5 6 4 9 ± 8 7 6 8 4 - 0 1 32 + 9 P 4 0 15 0 . 2 6 N 0 . 7 2 N G T 2 0 0 2 + 3 1 3 2 0 2 44 + 2 31 18 27 ± 44 6 8 8 - 0 O 38 + 5 P 19 0 81 2 . 15 N 0 . 5 5 N G T 2 0 0 5 + 3 1 2 2 0 5 4 + 2 31 12 10 ± 1 7 3 6 9 0 - 0 5 15 + 4 E 2 0 4 8 0 . 5 5 N 0 . 0 -G T 2 0 0 5 + 3 1 6 2 0 5 14 + 2 31 41 3 2 ± 6 6 6 9 5 - 0 3 26 + 4 P 4 0 5 8 0 . 8 9 N 0 . 0 - B 2 2 0 0 5 + 3 1 A G T 2 0 0 5 + 3 1 0 2 0 5 4 5 + 8 31 5 4 3 ± 6 7 6 9 0 - 0 7 41 + 9 E 5 0 6 9 1 . 2 8 N 0 . 0 N G T 2 0 0 5 + 3 0 4 2 0 5 4 8 + 2 3 0 2 6 28 + 137 68 5 -1 1 28 + 5 E 1 - - - 0 . 0 -G T 2 0 0 6 + 3 3 4 2 0 6 54 + 1 33 28 31 ± 22 71 1 0 4 3 8 2 + 3 8 1 2 0 4 8 0 . 5 6 N 1 . 5 2 N B 2 2 0 0 6 + 3 3 G T 2 0 0 7 + 3 1 1 2 0 7 5 + 3 31 6 3 6 ± 5 9 6 9 2 - 0 9 21 + 5 E 2 0 2 9 0 . 3 7 N 0 . 0 -G T 2 0 1 0 + 3 2 3 2 0 10 51 + 2 32 18 4 8 + 9 2 7 0 6 - 0 9 7 5 + 12 E 3 1 3 3 1 . 7 3 N 1 . 9 3 N 8 2 2 0 1 0 + 3 2 G T 2 0 1 1 + 3 3 1 2 0 1 1 22 + 2 33 8 3 ± 1 1 7 71 4 - 0 6 52 + 9 P 1 - - - 0 . 0 -G T 2 0 1 7 + 3 4 2 2 0 17 37 ± 2 34 17 57 ± 6 7 73 1 -1 0 32 + 7 E 1 - - - 0 . 0 _ G T 2 0 1 8 + 3 5 1 2 0 18 1 + 2 3 5 8 25 ± 5 9 7 3 8 - 0 6 24 + 5 P 19 1 0 1 1 .91 N 0 . 3 5 N G T 2 0 1 8 + 3 5 9 2 0 18 2 6 + 1 3 5 57 5 7 + 5 3 74 5 - 0 2 1 1 ± 2 P 19 0 8 8 1 . 9 7 N 0 . 0 -G T 2 0 1 8 + 3 6 3 2 0 18 41 + 1 36 22 12 ± 21 74 9 0 0 184 + 18 P 5 0 7 8 1 .31 N 0 . 0 - 4C 3 6 . 3 9 G T 2 0 2 4 + 3 8 8 2 0 24 24 + 1 38 5 3 2 6 ± 21 77 6 0 . 5 148 + 15 4 5 1 0 8 1 . 6 6 N 0 . 0 -G T 2 0 5 0 + 4 6 5 2 0 5 0 58 + 1 4 6 3 0 2 9 ± 52 8 6 6 1. 4 15 + 2 E 19 1. 14 2 . 2 9 N 0 . 0 _ G T 2 0 5 4 + 4 7 3 2 0 54 38 + 1 47 19 15 ± 34 8 7 6 1. 4 141 + 16 1 6 0 . 91 2 . 0 7 N 0 . 9 4 N G T 2 0 5 9 + 4 7 2 2 0 5 9 3 + 2 47 14 28 ± 1 2 4 8 8 . 1 0 . 8 37 + 9 P 5 0 . 9 7 1 . 4 7 N 1 . 18 N G T 2 0 5 9 + 4 6 1 2 0 5 9 26 + 1 4 6 8 19 + 3 0 87 . 3 0 . 0 6 9 + 8 P 2 0 0 . 8 0 1 .51 N 1 . 0 3 N G T 2 1 0 0 + 4 6 8 21 0 33 + 1 4 6 5 0 3 9 + 28 8 7 . 9 0 . 3 3 2 9 + 34 P 7 3 . 27 5 . 3 1 Y 5 . 3 6 Y G T 2 1 0 1 + 4 6 1 21 1 3 + 8 4 6 7 18 ± 1 9 8 8 7 . 5 - 0 . 2 51 + 14 P 7 0 . 9 7 2 . 2 4 N 0 . 4 3 N G T 2 1 0 1 + 4 6 6 21 1 32 + 3 4 6 37 5 8 ± 6 6 87 . 9 0 . 1 15 + 4 P 6 0 . 5 6 1 . 0 3 N 0 . 9 7 N G T 2 1 0 1 + 4 7 2 21 1 34 + 1 47 13 4 6 ± 72 8 8 . 3 0 . 5 17 + 2 4 2 0 0 . 7 6 1 . 7 2 N 0 . 0 -• T a b l e V I . C o n t i n u e d NAME R A ( 1 9 5 0 ) h ra s D E C ( 1 9 5 0 ) * / II 1 b F l u x D e n s i t y ( m d y ) D i a m N o . S h o r t V i V a r i a t i o n s T e r m V i V A R ? L o n g I n d e x T e r m V A R ? O t h e r C a t a l o g u e s G T 2 1 0 7 + 4 7 0 21 7 5 0 + 8 4 7 2 22 + 135 8 8 9 - 0 . 4 16 + 5 E 6 1 01 1. 4 5 N 0 0 -G T 2 1 0 8 + 4 6 2 21 8 0 + 1 4 6 17 4 0 ± 1 5 6 8 8 4 -1 . 0 4 0 + 6 P 5 0 8 6 1. 2 9 N 0 6 3 N G T 2 1 0 8 + 4 7 6 21 8 2 0 + 2 4 7 4 0 21 ± 1 2 6 8 9 4 - 0 . 1 21 + 3 P 6 0 6 6 1. 19 N 0 0 G T 2 1 0 8 + 4 5 9 21 8 21 + 1 4 5 54 17 ± 33 8 8 2 - 1 . 3 31 + 3 P 19 0 9 8 2 . 3 0 N 0 0 G T 2 1 0 8 + 4 9 1 21 8 34 + 4 4 9 6 5 2 ± 74 9 0 5 0 . 9 19 + 4 E 4 0 4 8 0 . 6 9 N 0 0 G T 2 1 0 8 + 4 8 8 21 8 5 0 + 2 4 8 5 3 3 0 ± 1 2 1 9 0 4 0 7 19 + 3 P 6 0 6 8 1 13 N 0 0 G T 2 1 0 9 + 4 8 9 21 9 1 1 + 2 4 8 57 2 6 ± 1 5 3 9 0 5 0 7 2 0 + 5 E 2 0 0 4 0 10 N 0 0 * G T 2 1 0 9 + 4 9 9 21 9 5 5 + 4 4 9 5 5 3 6 + 74 91 3 1 3 24 + 5 E 6 0 7 3 1 16 N 0 6 7 N G T 2 1 1 0 + 4 7 5 21 10 4 2 + 5 4 7 32 2 6 ± 1 9 8 8 9 6 - 0 5 2 5 + 4 E 5 0 57 0 91 N 0 0 — G T 2 1 1 1 + 4 5 9 21 1 1 16 ± 1 4 5 5 7 3 2 ± 35 8 8 5 -1 6 7 9 + 7 P 5 0 4 0 0 5 8 N 0 0 G T 2 1 1 1+482 21 1 1 21 + 2 48 17 4 5 ± 73 9 0 2 - 0 0 4 5 + 6 P 2 0 4 5 0 5 0 N 0 0 -G T 2 1 1 1 + 4 9 4 21 1 1 24 + 4 4 9 2 5 3 0 ± 67 91 1 0 8 3 5 + 6 E 18 1 2 3 3 44 P 1 2 7 N P K 0 8 8 - 0 1 . 1 G T 2 1 1 2 + 4 6 0 21 12 28 + 2 4 6 4 27 ± 42 8 8 8 -1 7 39 + 5 P 2 0 0 0 0 6 N 0 0 -G T 2 1 1 2 + 4 6 3 21 12 4 6 + 3 4 6 22 9 ± 7 9 8 9 0 -1 5 5 9 + 9 E 18 1 0 2 2 0 4 N 0 5 2 N G T 2 1 1 2 + 4 8 0 21 12 54 + 2 4 8 3 4 0 + 5 9 9 0 3 - 0 4 8 7 + 13 E 6 0 9 7 1 7 7 N 1 18 N G T 2 1 1 2 + 4 7 3 21 12 57 + 1 47 21 31 ± 34 8 9 8 - 0 9 74 + 8 P 5 0 6 0 1 OO N 1 2 8 N G T 2 1 1 3 + 4 6 7 21 13 2 0 + 2 4 6 44 27 ± 1 1 3 8 9 4 - 1 3 18 + 4 P 4 1 5 0 2 24 N 0 0 — 4C 4 8 . 5 3 G T 2 1 1 3 + 4 8 6 21 13 2 6 + 8 4 8 41 4 0 + 127 9 0 8 0 0 8 6 + 16 P 5 0 94 1 6 4 N 0 0 5 N G T 2 1 1 4 + 5 0 6 21 14 38 + 2 5 0 36 4 5 ± 56 9 2 3 1 2 18 + 3 P 5 0 7 3 1 3 6 N 0 0 ~ B G 2 1 1 4 + 4 9 G T 2 1 1 4 + 4 9 5 21 14 39 + 1 4 9 35 2 0 ± 2 3 91 6 0 5 168 + 17 P 16 0 8 6 2 11 N 1 84 N G T 2 1 1 5 + 5 1 1 21 15 31 + 1 51 8 24 ± 34 9 2 8 1 5 6 2 + 7 P 17 0 7 9 1 9 7 N 0 5 0 N G T 2 1 1 5 + 4 9 6 21 15 46 + 1 4 9 36 4 9 + 82 91 7 0 4 2 9 + 4 P 6 0 61 0 9 5 N 0 0 — G T 2 1 1 5 + 5 0 4 21 15 46 + 2 5 0 24 15 ± 8 0 9 2 3 0 9 2 5 + 5 P 2 0 4 0 0 41 N 0 0 L H E 5 0 0 G T 2 1 16+493 21 16 41 + 3 4 9 23 54 ± 44 91 6 0 1 27 + 5 P 17 1 22 3 51 Y 5 35 Y G T 2 1 17 + 4 6 8 21 17 1 + 1 4 6 5 3 5 3 + 47 8 9 9 -1 7 67 + 7 P 2 0 41 0 44 N 0 0 — G T 2 1 18+485 21 18 2 + 2 4 8 32 1 + 108 91 2 - 0 6 23 + 4 E 5 0 38 0 64 N 0 0 G T 2 1 1 9 + 5 0 4 21 19 32 + 1 5 0 25 3 8 ± 48 9 2 7 0 5 21 + 3 3 17 1 0 6 2 11 N 0 0 G T 2 1 2 0 + 4 8 8 21 2 0 33 + 2 4 8 5 3 44 + 198 91 7 - 0 7 2 0 + 3 E 6 0 8 2 1 6 5 N 0 0 G T 2 1 2 0 + 5 0 2 21 2 0 4 7 ± 2 5 0 12 4 5 ± 1 0 1 9 2 7 0 2 22 + 4 E 5 0 8 6 1 5 5 N 0 0 4 C 4 9 . 3 9 G T 2 1 2 0 + 4 9 1 21 2 0 53 • 1 4 9 8 5 5 ± 27 9 2 0 - 0 5 2 5 6 + 27 P 6 0 4 5 0 7 3 N 1 01 N G T 2 1 2 0 + 5 0 6 21 2 0 57 + 2 5 0 3 6 3 3 ± 6 5 9 3 0 0 5 15 + 4 P 3 0 9 9 1 36 N 0 0 ~ G T 2 1 2 2 + 4 8 4 21 22 16 + 2 48 29 15 ± 59 91 7 -1 2 16 + 4 P 16 0 78 1 9 3 N 0 0 6 N G T 2 1 2 2 + 4 8 8 21 22 22 + 1 4 8 51 31 ± 24 91 . 9 - 0 9 2 2 2 + 23 P 6 0 94 1 5 3 N 0 5 6 N G T 2 1 2 3 + 4 9 5 21 23 41 + 2 4 9 35 3 3 + 9 2 9 2 6 - 0 5 27 + 5 P 16 0 9 8 2 0 5 N 0 74 N G T 2 1 2 5 + 5 2 2 21 2 5 2 + 2 52 14 4 9 ± 1 7 6 94 6 1 2 27 + 5 P 5 0 6 2 0 84 N 0 0 ~ • G T 2 1 2 5 + 4 9 1 21 2 5 35 + 1 4 9 8 34 ± 47 9 2 . 5 -1 1 132 + 17 P 6 1 48 2 4 2 N 1 0 1 N G T 2 1 2 6 + 4 8 9 a 21 2 6 18 ± 8 4 8 5 8 14 ± 4 3 9 2 5 -1 3 2 9 0 + 41 1 6 1 32 2 12 N 2 11 N G T 2 1 2 6 + 4 8 9 b 21 2 6 3 6 + 2 4 8 5 6 4 3 ± 6 8 9 2 . 5 -1 3 5 0 + 10 P 6 1 32 2 12 N 0 . 0 N B G 2 1 2 7 + 5 0 G T 2 1 2 7 + 5 0 3 21 27 17 ± 1 5 0 2 3 3 9 ± 67 9 3 . 6 - 0 3 9 7 + 13 P 4 1 16 1 38 N 0 51 N G T 2 1 2 7 + 4 8 7 21 27 28 + 8 4 8 4 5 5 3 ± 41 9 2 . 5 -1 6 29 + 4 2 18 o 8 8 1 9 0 N 0 0 ~ G T 2 1 2 8 + 5 1 7 21 2 8 36 ± 3 51 4 7 44 ± 7 9 94 . 7 0 5 22 + 5 E 2 0 5 9 0 61 N 0 . 0 ~ G T 2 1 3 0 + 5 2 3 21 3 0 12 + 1 5 2 21 12 + 24 9 5 . 2 0 8 1 15 + 12 P 5 0 48 0 64 N 0 . 9 3 N G T 2 1 3 0 + 5 2 0 21 3 0 18 + 1 52 1 22 ± 25 9 5 . 0 0 5 133 + 14 P 5 0 6 6 0 9 8 N 2 . 4 6 N T a b l e V I . C o n t i n u e d NAME R A ( 1 9 5 0 ) h m s D E C ( 1 9 5 0 ) 1 b F l u x D e n s i t y ( m J y ) D i a m N o . S h o r t V , V a r i a t i o n s T e r m V . V A R ? L o n g . I n d e x T e r m VAR?. O t h e r C a t a l o g u e s G T 2 1 3 0 + 4 9 2 21 3 0 5 0 + 2 4 9 13 27 ± 6 7 9 3 2 -1 6 17 + 4 P 3 O 17 0 2 6 N 0 0 -G T 2 1 3 1 + 5 1 2 21 31 24 + 1 51 12 5 0 + 105 94 6 - 0 2 4 5 + 6 E 19 0 9 7 2 5 3 N 0 9 9 N G T 2 1 3 2 + 4 9 8 21 32 52 + 2 4 9 51 16 ± 9 2 9 3 9 -1 3 2 3 + 5 P 4 1 44 2 37 N 0 0 -G T 2 1 3 4 + 5 3 5 21 34 1 + 1 5 3 3 5 38 ± 44 9 6 5 1 3 159 + 18 P 6 0 81 1 15 N 0 12 N 0 X + 5 5 7 G T 2 1 3 4 + 5 3 1 21 34 3 0 + 1 5 3 1 1 4 ± 27 9 6 3 1 0 101 + 1 1 P 18 1 0 8 1 94 N 1 13 N G T 2 1 3 4 + 5 3 6 21 34 37 + 4 5 3 3 8 27 + 5 0 9 6 6 1 3 10 + 2 E 18 1 32 3 15 P 0 0 -G T 2 1 3 5 + 5 0 8 21 3 5 15 + 1 5 0 48 1 + 2 0 94 8 - 0 9 1229 ± 1 2 2 P 6 1 0 2 1 9 2 N 2 5 9 N G T 2 1 3 6 + 5 1 3 21 36 5 0 + 1 51 21 5 3 ± 24 9 5 3 - 0 6 3 5 8 + 36 P 4 0 6 4 1 0 7 N 0 0 2 N G T 2 1 3 7 + 5 2 6 21 3 7 26 + 2 52 3 9 13 + 185 9 6 3 0 3 16 + 3 P 4 0 84 1 4 0 N 0 0 -G T 2 1 3 8 + 5 2 7 21 38 12 + 1 52 4 6 31 + 2 5 9 6 4 0 3 121 + 13 P 5 0 8 3 1 27 N 2 6 6 N G T 2 1 3 8 + 5 2 6 21 38 25 + 2 52 3 6 2 6 + 5 9 9 6 3 0 1 2 9 + 5 E 2 0 38 0 4 4 N 0 0 -G T 2 1 3 9 + 5 3 4 21 3 9 8 + 2 5 3 24 27 + 72 9 6 9 0 7 2 6 + 5 P 17 0 8 0 2 0 1 N 0 7 6 N G T 2 1 4 0 + 5 1 6 21 4 0 47 + 1 51 4 0 32 + 24 9 6 0 - 0 8 178 + 18 P 5 1 0 3 1 5 5 N 0 0 4 N 4 C 5 1 . 4 6 G T 2 1 4 0 + 5 0 5 21 4 0 51 ± 1 5 0 32 9 + 9 3 9 5 3 - 1 7 32 + 3 P 6 0 4 9 0 7 6 N o 0 -G T 2 1 4 1 + 5 2 1 21 41 15 + 2 52 8 28 ± 1 5 2 9 6 4 - 0 5 2 5 ± 5 E 17 0 9 0 2 61 N 1 10 N G T 2 1 4 1 + 5 0 9 21 41 22 + 2 5 0 5 8 18 ± 84 9 5 6 -1 4 2 3 ± 5 P 2 0 72 0 7 8 N 0 0 — G T 2 1 4 1 + 5 1 5 21 41 39 + 8 51 34 51 ± 51 9 6 0 -1 0 31 ± 6 P 6 1 0 2 1 9 5 N 0 0 -G T 2 1 4 1 + 5 2 4 21 41 5 6 + 1 5 2 2 6 23 ± 51 9 6 6 - 0 3 124 ± 14 P 4 0 84 1 2 3 N 1 01 N G T 2 1 4 2 + 5 2 5 21 4 2 33 + 1 5 2 3 0 5 6 ± 2 3 9 6 8 - 0 3 136 ± 14 P 5 0 7 8 0 9 2 N 1 41 N G T 2 1 4 2 + 5 3 0 21 4 2 4 6 + 2 5 3 0 5 5 ± 1 1 6 9 7 1 0 0 19 ± 5 P 2 0 42 0 44 N 0 0 -G T 2 1 4 2 + 5 1 7 21 4 2 4 9 + 2 51 4 5 7 ± 5 6 9 6 3 -1 0 22 ± 5 P 17 0 6 3 1 3 3 N 1 6 8 N G T 2 1 4 3 + 5 3 9 21 4 3 1 1 + 5 5 3 5 5 51 + 4 6 97 7 0 7 28 + 6 P 2 0 13 0 13 N 0 0 -G T 2 1 4 3 + 5 4 4 21 4 3 29 + 1 54 28 8 + 24 9 8 1 1 1 117 + 12 P 5 0 2 8 0 4 9 N 1 0 2 N G T 2 1 4 3 + 5 3 2 21 4 3 38 ± 1 5 3 15 37 ± 64 9 7 4 0 1 19 + 3 P 17 0 61 1 0 9 N 0 0 -G T 2 1 4 4 + 5 3 1 21 44 56 + 6 5 3 9 19 + 8 5 97 4 - 0 1 8 8 + 16 P 7 1 0 5 2 32 N 1 24 N G T 2 1 4 4 + 5 2 2 21 44 58 + 6 5 2 13 12 ± 5 9 9 6 8 - 0 8 4 8 + 10 P 5 0 54 0 8 8 N 0 91 N G T 2 1 4 5 + 5 1 8 21 4 5 3 0 + 8 51 5 3 17 + 84 9 6 7 -1 1 24 + 5 P 7 0 9 9 1 6 6 N 0 0 -G T 2 1 4 6 + 5 2 0 21 4 6 47 + 3 5 2 4 5 7 ± 47 9 7 0 -1 1 4 2 + 7 P 6 0 3 9 0 6 3 N 0 22 N G T 2 1 4 6 + 5 2 6 21 4 6 4 9 + 2 5 2 38 5 9 ± 9 9 9 7 3 - 0 7 18 + 3 E 6 0 4 7 0 8 5 N 0 0 -G T 2 1 4 7 + 5 3 2 21 4 7 5 + 1 5 3 '17 4 0 ± 37 9 7 8 - 0 2 169 + 19 P 6 1 0 4 1 9 2 N 0 0 6 N 4C 5 3 . 4 9 G T 2 1 4 7 + 5 2 2 21 4 7 25 + 8 5 2 12 1 ± 1 8 3 9 7 1 -1 1 17 + 3 E 17 0 74 2 0 4 N 0 0 -G T 2 1 4 7 + 5 3 9 21 4 7 26 + 2 5 3 54 5 7 ± 5 9 9 8 2 0 3 18 + 3 P 6 0 8 5 1 .13 N 0 0 -G T 2 1 4 7 + 5 4 9 21 4 7 29 ± 8 54 5 9 5 0 ± 81 9 8 9 1 1 4 6 + 14 P 4 0 2 9 0 3 9 N 0 84 N G T 2 1 4 7 + 5 4 6 21 4 7 5 0 + 2 54 37 5 3 + 5 5 9 8 7 0 8 18 + 3 P 6 0 6 7 1 3 3 N 0 0 -G T 2 1 4 7 + 5 3 5 21 4 7 51 + 1 5 3 3 3 4 6 ± 24 9 8 0 - 0 0 8 9 + 9 P 7 0 9 9 1 5 6 N 0 9 7 N B G 2 1 4 7 + 5 3 B G T 2 1 4 8 + 5 5 0 21 4 8 37 + 1 5 5 2 31 ± 91 9 9 1 1 0 2 8 + 4 E 17 1 14 2 6 6 N 1 4 3 N G T 2 1 4 9 + 5 5 3 21 4 9 1 + 3 5 5 19 3 0 ± 1 3 7 9 9 3 1 2 2 3 + 5 E 17 0 72 1 5 9 N 0 2 7 N G T 2 1 4 9 + 5 3 2 21 4 9 4 6 + 2 53 13 31 ± 9 0 9 8 0 - 0 5 25 + 3 E 7 0 37 0 6 2 N 0 0 -G T 2 1 5 0 + 5 1 8 21 5 0 35 + 8 51 52 9 ± 1 5 3 9 7 3 -1 6 4 5 + 14 P 7 0 9 3 1 8 3 N 1 27 N G T 2 1 5 0 + 5 2 2 21 5 0 4 0 + 2 5 2 13 15 ± 77 9 7 5 -1 4 21 + 5 P 2 0 64 0 71 N 0 0 -G T 2 1 5 2 + 5 2 6 21 52 0 + 2 5 2 37 9 ± 6 3 97 9 -1 2 27 + 5 P 2 0 5 3 0 5 5 N o 0 -G T 2 1 5 2 + 5 3 0 21 52 26 + 3 5 3 3 15 ± 52 9 8 3 - 0 9 27 ± 6 P 17 0 8 5 1 6 0 N 0 6 8 N G T 2 1 5 2 + 5 4 8 21 5 2 4 3 + 1 54 51 37 + 35 . 9 9 4 0 5 71 ± 8 P 5 0 6 9 1 10 N 0 5 9 N 0 X + 5 8 8 T a b l e V I . C o n t i n u e d NAME R A ( 1 9 5 0 ) h m s D E C ( 1 9 5 0 ) ' / II 1 b F l u x D e n s i t y ( m J y ) D t a m N o . S h o r t V i V a r 1 a t I o n s T e r m Vt VAR? L o n g I n d e x T e r m VAR? O t h e r C a t a l o g u e s G T 2 1 5 4 + 5 6 4 21 5 4 10 + 1 5 6 24 13 ± 38 100 5 1 6 8 5 + 9 P 6 0 5 6 0 74 N 0 24 N G T 2 1 5 5 + 5 5 3 21 5 5 3 + 2 5 5 2 0 38 ± 8 0 100 0 0 7 27 + 5 P 18 0 8 2 1 8 4 N 1 44 N G T 2 1 5 5 + 5 3 2 21 5 5 10 + 2 5 3 17 21 + 9 2 9 8 7 - 0 9 26 + 5 P 5 . 0 6 9 1 37 N 0 0 -G T 2 1 5 5 + 5 2 0 21 5 5 44 + 2 52 4 4 6 ± 84 9 8 0 - 1 9 18 + 5 P 2 0 0 4 0 0 4 N 0 0 -G T 2 1 5 5 + 5 3 1 21 5 5 5 8 + 8 5 3 8 4 6 + 61 9 8 7 - 1 1 6 5 + 13 P 18 1 27 3 26 P 1 4 5 N G T 2 1 5 6 + 5 2 4 21 5 6 23 + 3 52 27 34 + 37 9 8 4 - 1 7 4 8 + 7 P 18 1 28 2 7 6 N 0 8 9 N G T 2 1 5 6 + 5 4 1 21 5 6 3 0 + 1 54 7 3 0 ± 41 9 9 4 - 0 4 103 ± 12 P 6 1 10 1 94 N 0 6 3 N 4C 5 4 . 4 5 G T 2 1 5 7 + 5 6 0 21 57 10 + 2 5 6 1 6 + 9 9 100 6 1 1 16 ± 3 P 4 0 36 0 6 8 N 0 0 -G T 2 1 5 7 + 5 5 6 21 5 7 22 + 2 5 5 3 9 5 7 + 112 100 4 0 8 17 + 3 E 6 0 8 2 1 21 N 0 0 -G T 2 1 5 7 + 5 6 0 21 57 25 + 5 5 6 5 24 + 47 100 7 1 1 52 + 10 P 6 0 8 2 1 4 5 N 0 2 3 N G T 2 1 5 7 + 5 6 6 21 5 7 4 5 + 1 5 6 41 4 9 ± 22 101 1 1 5 2 3 9 + 25 P 2 2 4 6 2 61 Y 1 27 N 4C 5 6 . 3 2 G T 2 1 5 7 + 5 5 4 21 5 7 5 3 + 2 5 5 26 54 ± 42 100 3 0 5 4 0 + 6 P 18 0 9 2 1 51 N 1 0 4 N G T 2 1 5 8 + 5 6 6 21 5 8 2 6 + 2 56 39 51 ± 76 101 1 1 5 26 + 5 P 5 0 34 0 71 N 0 0 -G T 2 1 5 8 + 5 5 2 21 5 8 41 + 2 5 5 14 2 9 ± 1 15 100 3 0 3 18 • 3 E 6 0 54 0 9 5 N 0 0 -G T 2 1 5 9 + 5 5 5 21 5 9 10 + 1 5 5 3 0 24 ± 26 100 5 0 5 128 + 13 1 5 0 9 3 1 37 N 0 38 N G T 2 2 0 1 + 5 3 9 22 1 22 + 2 5 3 57 38 + 5 3 9 9 9 -1 0 4 6 + 6 P 5 0 72 1 24 N 0 13 N G T 2 2 0 2 + 5 4 7 22 2 19 + 5 54 4 5 3 3 + 175 100 4 - 0 4 26 + 6 P 18 0 5 5 1 34 N 1 8 0 N G T 2 2 0 2 + 5 6 5 22 2 32 + 4 5 6 33 4 3 + 119 101 5 1 0 22 + 5 E 5 0 42 0 6 0 N 0 0 -G T 2 2 0 2 + 5 7 0 22 2 4 9 + 2 57 2 2 0 ± 6 2 101 8 1 4 3 0 + 5 P 6 0 5 0 0 81 N 1 28 N G T 2 2 0 3 + 5 5 9 22 3 4 6 + 1 5 5 54 5 7 ± 3 0 101 3 0 4 140 + 16 P 6 1 7 3 2 6 7 P 1 2 6 N 4C 5 5 . 4 0 G T 2 2 0 4 + 5 6 8 22 4 5 + 6 5 6 5 3 3 6 + 57 101 9 1 2 27 + 7 P 6 1 2 0 2 1 1 N 1 24 N G T 2 2 0 4 + 5 4 1 22 4 27 + 2 54 10 5 5 ± 7 6 100 4 -1 0 32 + 7 P 6 0 77 1 2 9 N 0 5 2 N G T 2 2 0 6 + 5 5 3 22 6 6 + 8 5 5 21 2 2 + 133 101 2 - 0 2 5 0 + 1 1 P 6 0 6 3 1 1 1 N 0 9 3 N G T 2 2 0 6 + 5 6 7 2 2 6 23 + 8 5 6 4 2 9 ± 5 9 102 0 0 9 8 9 + 2 0 E 4 0 13 0 27 N 0 6 8 N G T 2 2 0 7 + 5 6 9 22 7 37 + 3 5 6 5 9 3 0 + 6 0 102 3 1 0 36 + 6 P 6 0 74 1 38 N 0 5 7 N O Y + 5 1 2 G T 2 2 0 9 + 5 3 8 22 9 39 ± 8 5 3 53 2 3 ± 7 0 100 8 -1 7 41 + 10 E 2 0 24 0 3 3 N • 0 0 ~ G T 2 2 1 1 + 5 5 4 22 1 1 5 0 + 1 5 5 24 31 ± 6 3 101 9 - 0 6 42 + 7 P 18 0 61 0 9 8 N 3 8 3 Y G T 2 2 1 1 + 5 5 8 22 1 1 54 + 4 5 5 4 9 4 8 ± 1 9 1 102 2 - 0 3 2 8 + 6 P 18 0 81 1 84 N 0 13 N G T 2 2 1 2 + 5 8 1 22 12 16 + 8 5 8 7 5 3 ± 1 2 6 103 5 1 6 31 + 8 E 5 o 4 3 0 71 N 0 0 -G T 2 2 1 4 + 5 6 7 22 14 0 + 1 5 6 44 10 ± 2 0 102 9 0 3 4 2 8 + 4 3 P 17 0 8 0 1 5 2 N 0 0 8 N 4C 5 6 . 3 3 G T 2 2 1 4 + 5 4 1 22 14 2 + 2 54 7 5 ± 1 2 9 101 5 -1 9 12 + 3 P 5 0 2 0 0 19 N 0 0 -G T 2 2 1 4 + 5 7 2 22 14 9 + 5 5 7 13 5 0 ± 1 9 8 103 2 0 7 25 + 6 P 4 0 14 0 36 N 0 0 -G T 2 2 1 4 + 5 4 5 22 14 34 + 2 54 3 0 16 ± 54 101 7 -1 6 25 + 5 P 6 0 4 5 0 84 N 0 5 3 N G T 2 2 1 6 + 5 8 6 22 16 5 9 + 2 5 8 36 4 5 ± 9 2 104 3 1 6 35 + 7 P 2 1 38 1 42 N 0 0 -G T 2 2 1 8 + 5 7 9 22 18 25 + 2 57 5 9 5 5 ± 47 104 1 1 0 71 + 8 2 6 0 47 O 7 5 N 0 13 . N G T 2 2 1 9 + 5 5 3 22 19 23 + 2 5 5 18 27 ± 6 9 102 8 -1 3 31 + 4 P 6 0 6 6 1 0 5 N 0 0 -G T 2 2 2 0 + 5 6 7 22 2 0 5 + 4 5 6 47 9 ± 57 103 6 - 0 1 21 + 4 P 6 0 18 0 27 N 0 0 G T 2 2 2 1 + 5 7 9 22 21 5 5 + 2 57 57 4 2 ± 39 104 5 0 7 28 + • 4 2 17 0 9 9 2 6 5 N 2 7 7 N G T 2 2 2 2 + 5 7 6 22 22 4 3 + 2 57 39 6 ± 74 104 4 0 4 21 + 3 P 6 0 8 7 1 34 N 0 0 -G T 2 2 2 2 + 5 7 2 22 22 51 + 1 57 13 1 + 6 5 104 2 0 0 32 + 4 P 6 0 7 3 1 27 N 0 0 -G T 2 2 2 3 + 5 8 9 22 2 3 12 + 4 5 8 55 5 3 + 198 105 1 1 5 19 + 5 P 4 0 4 5 0 6 4 N 0 0 -G T 2 2 2 3 + 5 7 9 22 2 3 36 + 1 57 57 14 ± 3 0 104 7 0 6 143 + 15 5 18 0 6 0 1 14 N 0 3 5 N G T 2 2 2 3 + 5 7 3 22 2 3 52 + 2 57 19 2 9 + 5 5 104 4 0 1 42 + 6 P 2 0 5 5 0 6 3 N 0 0 T a b l e V I . C o n t i n u e d NAME R A ( 1 9 5 0 ) h m s D E C ( 1 9 5 0 ) F l u x D e n s i t y ( m d y ) D i a m N o . V a r l a t I o n s S h o r t T e r m V , V , V A R ? L o n g T e r m I n d e x V A R ? O t h e r C a t a l o g u e s G T 2 2 2 6 + 5 8 9 22 26 2 3 + 1 5 8 5 8 8 ± 38 105 5 1 3 103 + 1 1 P 3 0 84 1 19 N 1 9 6 N G T 2 2 2 8 + 5 8 7 22 28 2 + 1 5 8 42 2 3 ± 28 105 6 1 0 130 + 14 P 18 0 9 2 2 3 5 N 0 8 2 N G T 2 2 3 0 + 5 8 7 22 3 0 3 + 7 58 4 3 16 ± 1 0 1 105 8 0 8 3 0 + 5 P 6 0 71 1 3 3 N 0 0 -G T 2 2 3 0 + 5 9 1 22 3 0 4 2 + 2 5 9 8 14 ± 1 19 106 1 1 1 17 + 3 P 5 0 5 2 0 9 7 N 0 0 -G T 2 2 3 1 + 5 8 1 2 2 31 5 3 + 2 58 1 1 5 9 ± 64 105 7 0 3 28 + 4 E 6 0 77 1 5 5 N 0 0 -G T 2 2 3 2 + 5 9 0 22 32 37 + 8 5 9 4 41 ± 56 106 3 1 0 5 2 9 P 6 0 9 0 1 3 0 N 0 16 N G T 2 2 3 3 + 5 7 4 2 2 3 3 3 2 + 2 57 28 3 8 ± 1 5 4 105 6 - 0 5 2 0 + 5 E 4 0 5 2 0 8 5 N 0 0 -G T 2 2 3 3 + 5 6 8 22 3 3 5 8 + 8 5 6 51 44 ± 41 105 3 - 1 0 37 + 6 P 17 1 0 2 2 41 N 0 15 N G T 2 2 3 4 + 5 7 9 22 34 51 + 8 5 7 5 8 3 9 + 9 9 106 0 - 0 1 22 + 6 P 5 0 5 3 0 9 3 N 0 0 -G T 2 2 3 4 + 5 9 2 22 34 52 + 8 5 9 16 27 ± 1 9 8 106 6 1 0 41 + 8 P 6 0 71 1 16 N 0 0 2 N G T 2 2 3 4 + 5 7 2 22 34 5 2 + 2 5 7 14 13 + 7 3 105 6 - 0 8 39 + 6 P 2 0 12 0 23 N 0 0 -G T 2 2 3 5 + 5 8 5 22 3 5 4 5 + 2 5 8 3 0 36 ± 6 0 106 3 0 3 7 3 + 9 1 17 1 18 2 9 2 P 0 6 3 N G T 2 2 3 6 + 5 9 5 22 3 6 13 + 8 5 9 35 3 9 ± 1 0 5 106 9 1 2 34 + 10 E 17 0 8 6 1 6 6 N 0 8 9 N G T 2 2 3 6 + 6 0 0 22 3 6 3 3 + 3 6 0 5 15 ± 1 0 3 107 2 1 6 34 + 6 P 17 0 8 3 1 26 N 2 28 N G T 2 2 3 7 + 5 9 9 22 37 21 + 1 5 9 5 6 22 ± 33 107 2 1 4 78 + 9 P 17 1 11 2 15 N 0 94 N G T 2 2 3 8 + 5 7 2 22 3 8 2 5 + 1 57 17 0 ± 27 106 0 -1 0 207 + 22 P 17 0 9 2 1 6 6 N 1 5 0 N G T 2 2 3 9 + 5 8 7 22 3 9 10 + 2 5 8 43 13 ± 9 2 106 8 0 2 4 0 + 7 P 6 0 5 7 1 10 N 1 31 N G T 2 2 3 9 + 5 7 2 22 3 9 52 + 2 57 12 5 2 ± 5 9 106 2 -1 1 36 + 6 P 17 0 9 3 1 8 3 N 2 0 5 N G T 2 2 4 0 + 5 8 0 22 4 0 4 + 8 5 8 3 32 ± 57 106 6 - 0 4 52 + 9 P 17 0 91 2 2 6 N • 0 9 2 N G T 2 2 4 1 + 6 0 6 22 41 21 + 8 6 0 4 0 38 ± 5 3 108 0 1 8 58 ± 17 E 5 1 64 2 19 P 1 2 9 N G T 2 2 4 2 + 5 7 7 2 2 42 3 + 2 57 47 2 9 ± 71 106 7 - 0 7 21 ± 3 P 5 0 3 9 0 6 3 N 0 0 -G T 2 2 4 3 + 5 8 5 22 4 3 32 + 6 5 8 3 5 10 ± 8 5 107 3 - 0 1 88 ± 16 E 6 0 5 6 1 2 3 N 0 11 N G T 2 2 4 4 + 6 0 0 22 44 16 + 5 6 0 0 2 5 ± 1 2 2 108 0 1 1 2 0 + 4 P 6 0 2 3 0 3 6 N 0 0 -G T 2 2 4 4 + 5 8 8 22 44 31 ± 2 5 8 5 3 3 6 ± 8 7 107 5 0 1 27 + 5 E 5 0 7 9 1 24 N 0 0 -G T 2 2 4 5 + 6 0 6 2 2 4 5 3 6 ± 2 6 0 37 7 ± 91 108 4 1 6 26 + 6 E 2 0 4 6 0 5 5 N 0 0 -G T 2 2 4 6 + 6 0 3 2 2 4 6 3 + 1 6 0 22 0 ± 44. 108 4 1 3 6 0 + 7 1 5 0 9 5 1 4 6 N 1 51 N G T 2 2 4 6 + 5 9 6 22 4 6 54 + 8 5 9 38 2 6 ± 4 5 108 1 0 6 101 + 14 P 6 0 7 5 1 52 N 3 8 5 Y G T 2 2 4 7 + 5 7 5 22 4 7 2 9 + 1 57 3 0 4 6 ± 1 0 2 107 2 -1 3 8 0 + 10 5 6 1 0 4 1 6 2 N 0 0 N G T 2 2 4 8 + 5 9 6 2 2 4 8 41 + 2 5 9 38 5 9 ± 54 108 3 0 5 53 + 10 P 6 0 5 0 0 94 N 1 51 N G T 2 2 4 9 + 5 8 2 2 2 4 9 5 + 2 5 8 16 2 9 ± i 1 8 107 8 - 0 7 28 + 5 E 6 0 71 1 4 8 N 0 0 -G T 2 2 4 9 + 5 9 5 22 4 9 19 + 1 5 9 32 3 5 ± 39 108 4 0 4 6 0 + 7 P 6 0 7 5 1 14 N 2 0 3 N G T 2 2 4 9 + 5 9 2 2 2 4 9 37 + 8 5 9 14 26 ± 41 108 3 0 1 44 + 6 1 17 0 8 5 1 6 9 N 0 6 6 N G T 2 2 5 1 + 6 0 4 2 2 51 4 3 + 7 6 0 27 24 ± 41 109 0 1 1 224 + 25 P 14 0 6 9 1 3 3 N 0 44 N G T 2 2 5 1 + 5 9 8 2 2 51 4 5 + 2 5 9 4 9 2 ± 78 108 8 0 5 31 + 5 P 14 0 9 5 2 27 N 1 6 7 N G T 2 2 5 2 + 5 9 1 22 5 2 16 + 8 5 9 6 54 ± 1 9 8 108 5 - 0 2 39 + 12 P 14 0 8 8 2 0 8 N 0 9 5 N G T 2 2 5 2 + 5 7 6 2 2 5 2 51 + 1 57 4 0 4 9 + 2 5 108 0 -1 5 1236 ± 1 2 4 P 14 0 5 7 0 9 2 N 0 0 6 N G T 2 2 5 3 + 5 9 1 2 2 5 3 0 + 1 5 9 1 1 27 ± 24 108 6 - 0 1 72 + 6 P 6 0 5 0 1 2 0 N 0 0 -G T 2 2 5 3 + 5 8 2 22 5 3 2 9 + 1 58 12 5 5 ± 39 108 3 -1 0 6 6 + 7 P 6 0 44 0 76 N 3 34 P G T 2 2 5 3 + 5 9 4 22 5 3 4 3 + 5 5 9 2 9 2 ± 8 0 108 8 0 1 31 + 7 E 5 1 0 3 1 5 9 N 0 5 6 N G T 2 2 5 5 + 5 9 7 22 5 5 5 8 + 3 5 9 44 14 ± 84 109 2 0 2 23 + 5 P 5 0 5 2 0 9 3 N 0 17 N G T 2 2 5 6 + 6 1 2 22 5 6 0 + 3 61 13 3 0 ± 77 109 8 1 5 28 + 6 P 2 0 2 0 0 23 N O 0 -G T 2 2 5 7 + 5 8 0 2 2 57 4 + 2 5 8 0 1 ± 58 108 6 -1 4 35 + 6 P 6 1 2 9 2 74 N 0 5 8 N G T 2 2 5 7 + 5 7 7 22 57 54 + 5 5 7 42 2 3 ± 25 108 6 -1 8 84 + 1 1 E 16 1 3 6 3 0 2 P 0 8 9 N B G 2 2 3 8 + 5 7 B G 2 2 5 2 + 5 7 cn T a b l e V I C o n t 1 n u e d N A M E R A ( 1 9 5 0 ) h m s D E C ( 1 9 5 0 ) 1 b F l u x D e n s i t y ( m J y ) D 1 a m N o . S h o r t V i V a r 1 a t i o n s T e r m V * V A R ? L o n g I n d e x T e r m V A R ? O t h e r C a t a l o g u e s G T 2 2 5 7 + 5 9 9 2 2 5 7 5 4 + 1 5 9 5 5 3 ± 5 9 1 0 9 5 0 3 8 2 + 12 P 6 0 3 7 0 6 0 N 1 5 4 N G T 2 2 5 9 + 6 1 0 2 2 5 9 3 9 + 4 6 1 1 17 ± 6 3 1 1 0 1 1 2 2 7 + 6 P 16 1 12 2 2 8 N 0 7 4 N G T 2 3 0 0 + 6 1 6 2 3 0 0 + 3 6 1 4 0 16 + 6 7 1 1 0 4 1 8 2 4 + 6 P 16 0 6 6 1 1 2 N 1 2 1 N G T 2 3 0 0 + 5 7 7 2 3 0 5 7 + 1 5 7 4 6 3 8 ± 2 6 1 0 9 0 -1 9 4 9 8 + 5 0 2 1 - - - 0 0 N G T 2 3 0 3 + 6 1 2 2 3 3 56 + 1 6 1 17 2 2 ± 2 8 1 1 0 7 1 2 1 6 9 + 18 P 5 0 4 7 0 8 9 N 1 0 7 G T 2 3 0 5 + 6 0 4 2 3 5 5 2 + 2 6 0 2 8 5 2 ± 5 2 1 1 0 6 0 4 17 + 3 P 16 0 7 8 1 8 6 N 0 0 -G T 2 3 0 6 + 5 9 4 2 3 6 16 + 2 5 9 2 9 5 1 ± 6 2 1 1 0 3 - 0 6 2 3 + 5 P 2 0 0 2 0 0 4 . N 0 0 -G T 2 3 0 6 + 5 9 1 2 3 6 2 3 + 2 5 9 9 3 9 + 8 7 1 1 0 2 - 0 9 3 7 + 6 E 16 1 0 7 2 5 9 N 0 8 7 N G T 2 3 0 6 + 5 9 4 2 3 6 4 7 + 2 5 9 2 6 3 9 ± 1 5 4 1 1 0 3 - 0 6 3 1 + 4 E 6 0 9 8 1 7 6 N 0 0 G T 2 3 0 7 + 6 0 8 2 3 7 5 6 + 5 6 0 5 2 1 0 + 9 3 1 1 1 0 0 6 3 3 + 6 P 5 0 8 8 1 5 1 N 0 0 -G T 2 3 0 8 + 5 9 9 2 3 8 18 + 1 5 9 5 4 1 1 + 5 4 1 1 0 7 - 0 3 6 1 + 7 4 5 0 8 7 1 4 2 N 0 0 -G T 2 3 0 8 + 6 0 8 2 3 8 4 4 + 2 6 0 5 3 2 3 + 7 8 1 1 1 1 0 6 2 5 + 5 P 2 0 6 2 0 6 4 N 0 0 N G T 2 3 0 9 + 6 1 2 2 3 9 0 + 1 6 1 14 4 1 + 2 8 1 1 1 3 0 9 1 4 2 + 15 P 5 0 4 5 0 7 4 N 1 7 8 G T 2 3 3 5 + 6 0 3 2 3 3 5 3 2 + 1 6 0 2 0 5 2 ± 2 8 1 14 0 -1 0 1 0 8 + 12 1 17 0 9 6 1 7 3 N 0 9 0 N G T 2 3 3 6 + 6 3 1 2 3 3 6 1 2 + 6 63 1 0 5 0 ± 1 1 3 1 14 9 1 7 2 8 + 6 E 6 0 3 7 0 5 1 N 1 6 0 N G T 2 3 3 9 + 5 9 5 2 3 3 9 2 1 + 1 5 9 3 3 2 4 + 3 3 1 14 3 -1 9 2 4 5 + 2 5 P 17 1 0 2 2 7 3 N 1 6 3 N G T 2 3 4 1 + 6 3 2 2 3 4 1 5 + 8 6 3 13 4 8 ± 6 4 1 15 4 1 6 3 8 + 7 P 6 0 8 3 1 3 7 N 0 0 -G T 2 3 4 1 + 6 2 7 2 3 4 1 2 2 + 2 6 2 4 3 4 0 ± 1 1 4 1 1 5 3 1 1 6 3 + 12 P 1 - - 0 0 G T 2 3 4 1 + 6 3 0 2 3 4 1 3 1 + 8 6 3 0 5 4 ± 5 7 1 15 4 1 4 3 3 + 7 P 18 0 6 5 1 6 6 N 0 0 N G T 2 3 4 1 + G 1 3 2 3 4 1 4 4 + 1 6 1 19 4 7 ± 5 2 1 1 5 0 - 0 2 5 1 + 8 P 6 0 9 0 1 5 3 N 0 8 9 N G T 2 3 4 1 + 6 2 2 2 3 4 1 5 9 + 2 6 2 12 4 5 ± 1 3 4 1 1 5 3 0 6 . 2 5 + 5 E 6 0 4 7 0 7 1 N 0 0 -G T 2 3 4 3 + 6 1 0 2 3 4 3 18 + 1 6 1 0 6 ± 3 8 1 15 1 - 0 6 3 0 + 4 P 17 0 9 2 1 9 3 N 0 0 N G T 2 3 4 3 + 6 0 4 2 3 4 3 2 1 + 1 6 0 2 7 3 6 ± 1 6 6 1 1 5 0 -1 1 3 9 + 7 E 17 0 5 8 1 5 8 N 2 8 9 G T 2 3 4 4 + 6 2 2 2 3 4 4 5 6 + 2 6 2 16 2 9 ± 1 9 8 1 1 5 6 0 6 5 0 + 7 E 6 0 8 6 1 3 7 N 1 0 6 N . G T 2 3 4 4 + 6 0 9 2 3 4 4 5 8 + 1 6 0 5 8 5 6 ± 3 0 1 15 3 - 0 7 1 0 2 + 1 1 P 18 0 7 8 1 7 5 N 0 7 8 N G T 2 3 4 5 + 6 1 5 2 3 4 5 2 8 + 1 6 1 3 5 12 ± 8 3 1 1 5 5 - 0 1 8 1 + 1 1 P 18 0 8 0 2 0 4 N 2 7 2 N G T 2 3 4 8 + 6 0 0 2 3 4 8 5 4 + 8 6 0 2 4 1 ± 7 4 1 15 6 -1 7 9 5 + 19 P 17 0 9 0 1 8 0 N 0 9 7 N O Z + 6 8 2 G T 2 3 4 9 + 6 0 6 2 3 4 9 19 + 1 6 0 3 9 4 3 ± 2 3 1 15 8 -1 1 1 7 6 + 18 P 17 0 9 6 2 2 6 N 1 8 5 N G T 2 3 5 2 + 6 0 2 2 3 5 2 5 2 + 1 6 0 14 3 6 ± 3 4 1 16 1 -1 6 8 1 + 9 2 5 1 3 1 2 2 3 N 0 4 5 N G T 2 3 5 3 + 6 3 0 2 3 5 3 3 9 + 6 6 3 3 3 ± 1 3 2 1 16 8 1 1 15 + 4 P 6 0 9 2 1 5 2 N 0 0 -G T 2 3 5 3 + 6 1 2 2 3 5 3 4 3 + 1 6 1 1 5 5 3 ± 4 7 1 16 4 - 0 6 6 7 + 9 P 6 0 4 4 0 7 6 N 0 0 -G T 2 3 5 7 + 6 1 9 2 3 5 7 3 9 + 1 6 1 5 4 5 7 ± 3 9 1 1 7 0 - 0 1 1 4 4 + 14 4 1 0 0 3. Sources C o - i n c i d e n t with O p t i c a l Objects 155 The l i s t of compact sources provided i n t a b l e VII r e p r e s e n t s the most s e n s i t i v e catalogue of r a d i o sources, c o v e r i n g a l a r g e p o r t i o n of the g a l a c t i c plane, p r e s e n t l y a v a i l a b l e . A l a r g e m a j o r i t y of the sources were p r e v i o u s l y unknown; having f l u x d e n s i t i e s of tens of mJy, which i s w e l l below the t h r e s h o l d of e a r l i e r surveys. The presence of t h i s unique data base r a i s e s the q u e s t i o n of the o r i g i n s of these sources. It i s n a t u r a l to assume that some f r a c t i o n of the sources r e s i d e i n our own galaxy, a s s o c i a t e d with such o b j e c t s as; compact or d i s t a n t HII r e g i o n s , p l a n e t a r y nebulae, supernova remnants or r a d i o s t a r s . The e x i s t e n c e of a g a l a c t i c component of the compact sources i s examined i n a s t a t i s t i c a l sense in chapter V I I I . On an i n d i v i d u a l b a s i s , p o s s i b l e a s s o c i a t i o n with o p t i c a l o b j e c t s was i n v e s t i g a t e d by searching o p t i c a l catalogues f o r o b j e c t s p o s i t i o n a l l y c o - i n c i d e n t with the r a d i o sources. The major part of the search was c a r r i e d out using a tape catalogue of a s t r o n o m i c a l data provided by the Goddard Space F l i g h t Centre. Included on the tape are: the Smithsonian  A s t r o p h y s i c a l Observatory Star Catalogue ; the Catalogue of  S t e l l a r I d e n t i f i c a t i o n s , which c o n t a i n s about 431,000 e n t r i e s from v a r i o u s smaller c a t a l o g u e s ; De Vaucouler's Galaxy  Catalogue ; and The Two Micron Sky Survey (Neugebauer and L e i g h t o n , 1969). A computer program to c a r r y out a search for o b j e c t s on the tape with a s p e c i f i e d p o s i t i o n was produced at U.B.C. by Alex Szabo. Radio source c o - o r d i n a t e s were a l s o 156 compared to e n t r i e s i n both A Comparison Catalogue of HII  Regions (Marsalkova, 1973) and the Catalogue of G a l a c t i c  P l a n e t a r y Nebulae (Perek and Kohoutek, 1967). P o s i t i o n s were co n s i d e r e d to be c o - i n c i d e n t i f the d i f f e r e n c e , i n each co-o r d i n a t e , was l e s s than the one sigma e r r o r on the d i f f e r e n c e , c a l c u l a t e d from the e r r o r s on each p o s i t i o n . In some cases, such as the presence of a b r i g h t s t a r j u s t o u t s i d e the one sigma l i m i t , d i f f e r e n c e s l a r g e r than one sigma have been accepted. However, i n no case i s the d i f f e r e n c e g r e a t e r than twice sigma. The search y i e l d e d twenty—nine p o s i t i o n a l c o — i n c i d e n c e s ; eighteen with s t a r s , four with p l a n e t a r y nebulae, four with HII regions and three with sources of two micron e m i s s i o n . These r e s u l t s are l i s t e d i n t a b l e V I I I . The f i r s t column giv e s the survey source name. Columns 2 and 3 give the epoch 1950 co-o r d i n a t e s of the r a d i o source and the a s s o c i a t e d o b j e c t , and columns 4 and 5 give the d i f f e r e n c e between the c o - o r d i n a t e s of each, as w e l l as the estimated u n c e r t a i n t y on the d i f f e r e n c e . Since s t e l l a r c o - o r d i n a t e s are, i n ge n e r a l , known to about an arc-second, f o r s t e l l a r a s s o c i a t i o n the quoted u n c e r t a i n t y i s the one sigma e r r o r on the r a d i o c o - o r d i n a t e . Column 6 give s the d e s i g n a t i o n of the a s s o c i a t e d o b j e c t . For s t a r s , the SAO d e s i g n a t i o n has been given p r e f e r e n c e . Objects from the Catalogue of S t e l l a r I d e n t i f i c a t i o n s are p r e f i x e d with a ' C . Two micron sources and p l a n e t a r y nebulae are p r e f i x e d with 'TM' and 'PN', r e s p e c t i v e l y , followed by the c o - o r d i n a t e d e s i g n a t i o n used i n the o r i g i n a l c a t a l o g u e s . When a v a i l a b l e , the magnitude 1 57 of the o p t i c a l o b j e c t s i s l i s t e d i n column 7. For two micron sources, the K magnitude at 2.2» i s g i v e n . Column 8 gi v e s the s p e c t r a l type, f o r s t e l l a r o b j e c t s , or, simply, ' H l l ' o r 'PN' f o r HII regions and p l a n e t a r y nebulae. At l e a s t two of the p l a n e t a r y nebulae have been p r e v i o u s l y d e t e c t e d as r a d i o sources (Higgs 1971), and the a l t e r n a t e r a d i o d e s i g n a t i o n s are i n c l u d e d i n t a b l e V I I . However, i t i s to be expected that a number of the p o s i t i o n c o - i n c i d e n c e s , p a r t i c u l a r l y those with s t e l l a r o b j e c t s , are random events. C l e a r l y , a d d i t i o n a l evidence i s r e q u i r e d to determine whether or not any of the o b j e c t s are p h y s i c a l l y r e l a t e d to the r a d i o sources. I t i s noteworthy, however, that two of the short-term v a r i a b l e s appear in the t a b l e ; GT0236+610 and GT2116+493. In choosing a random sample of 29 elements from a set of 806, the chance of i n c l u d i n g 2 elements from a subset of 12 (short-term v a r i a b l e s ) of the 806, i s low enough to lend a d d i t i o n a l c r e d i b i l i t y to these a s s o c i a t i o n s . In f a c t , one of them (GT0236+610) has been confirmed (Gregory et a l . , 1979). The s t a r c o - i n c i d e n t with GT2116+493 i s w i t h i n the s p e c t r a l - t y p e range of the RS CVn c l a s s of r a d i o s t a r . T a b l e V I I O p t i c a l P o s i t i o n C o - I n c i d e n c e s S o u r c e R A ( 1 9 5 0 ) ( r a d i o s o u r c e ) ( O b j e c t ) D E C ( 1 9 5 0 ) lAcr l |A6| ( r a d i o s o u r c e ) ( s e c ) ( " ) ( O b j e c t ) O b j e c t M a g . S p e c t r a l T y p e GT0121+637 1 21 44 63 43 2 4 .0 + 6 122 ± 1 0 3 K 8 HI I 1 21 48 .00 63 41 0 .0 GT0123+616 1 23 35 61 36 22 8 . 1 + 8 3 ± 60 SAO 1 1759 8 .8 KO 1 23 26 .86 61 36 25 .4 GT0152+620 1 52 22 62 3 39 1 . 2 + 8 21 ± 48 C 183645 11 .4 B-1 52 20 .82 62 3 17 .6 GT0152+617 1 52 33 61 44 5 0 .4 + 8 13 ± 65 C 181805 12 .2 B 1 52 33 .35 61 44 18 . 2 GT0154+630 1 54 1 63 5 17 3 . 3 + 3 35 + 54 P N 130+1 1 15 .0 P N 1 53 57 .70 63 4 42 .0 GT0236+610 2 36 40 61 1 52 0 .7 + 4 62 ± 99 C 181753 11 .4 B 2 36 40 .68 61 0 50 .0 GT0252+586 2 52 27 58 38 42 • 2 .7 + 4 91 ± 87 SAO 23710 9 .2 K2 2 52 29 .68 58 40 13 4 GT0306+595 3 6 57 59 33 25 0 .5 + 8 76 ± 1 9 8 c 175367 A1 3 6 56 48 59 32 8 2 GT0308+585 3 8 4 58 30 48 1 7 + 1 1 17 ± 1 0 3 SAO 23865 8 3 B9 3 8 2 31 58 32 45 1 GT0309+563 3 9 57 56 18 46 8 0 + 8 44 ± 43 SAO 23884 9 1 F2 3 9 49 00 56 19 30 7 GT0313+591 3 13 36 59 7 2 1 4 + 2 37 ± 81 SAO 23926 8 9 A2 3 13 34 57 59 7 39 2 GT0338+544 3 38 13 54 28 3 2 3 + 4 89 + 76 SAO 24 164 9 4 F8 3 38 15 27 54 26 33 6 GT0344+539 3 44 3 53 59 8 5 7 + 4 99 ± 1 8 3 SAO 24421 8 8 GO 3 43 57 31 53 57 28 8 GT0510+400 5 10 17 40 3 26 0 2 + 1 6 ± 34 C 132117 1 1 5 B 5 10 16 82 40 3 19 8 GT0559+214 5 59 39 21 29 57 0 6 + 2 13 ± 66 C 69418 11 4 G5 5 59 39. 59 21 30 10. 8 GT0610+179 6 10 13 17 59 48 1 . 0 + 6 48 ± 65 S 255 HII 6 10 12. 00 17 59 0. 0 GT0G10+185 6 10 25 18 35 23 1 . 0 ± 2 19 ± 97 MT+20138 1 . 6 _ 6 10 26. 00 18 33 42. 0 GT0646+002 6 46 38 0 12 12 o. 1 + 1 88 ±191 C 3456 10. 8 B 6 46 37 . 92 0 10 44 . 0 GT1938+215 19 38 35 21 33 24 1. 9 + 2 38 ± 1 9 8 SAO 87553 8. 7 KO 19 38 33. 10 21 32 45. 2 GT1947+267 19 47 6 26 43 23 6. 0 + 6 37 ± 65 S 90 HII 19 47 12. 00 26 44 0. 0 GT1953+291 19 53 2 29 9 14 0. 9 + 2 3 ± 39 P N 65+0.1 16. 0 P N 19 53 2. 90 29 9 17 . 0 T a b l e V I I . C o n t i n u e d S o u r c e R A ( 1 9 5 0 ) ( r a d i o s o u r c e ) ( O b j e c t ) D E C ( 1 9 5 0 ) ( r a d i o s o u r c e ) ( O b j e c t ) Ua| ( s e c ) |A6| ( " ) O b j e c t M a g . S p e c t r a l T y p e G T 2 0 0 2 + 3 1 3 2 0 2 4 4 31 18 2 7 1 . 1 + 2 2 4 ± 4 4 P N 6 8 - 0 . 1 P N 2 0 2 4 5 1 0 3 1 18 5 1 . 0 G T 2 1 0 1 + 4 6 1 2 1 1 3 4 6 7 18 2 . 1 + 8 6 + 1 9 8 S A O 5 0 3 8 9 9 . 3 B 8 2 1 1 0 8 8 4 6 7 2 4 . 3 G T 2 1 1 6 + 4 9 3 21 16 4 1 4 9 2 3 5 4 3 . 0 + 3 1 ± 4 4 S A O 5 0 6 9 4 11 . 5 F 8 2 1 16 4 3 9 8 4 9 2 3 5 5 . 3 G T 2 1 4 7 + 5 2 2 2 1 4 7 2 5 5 2 12 1 5 . 0 + 8 4 9 + 1 8 3 M T + 5 0 4 0 1 1 . 9 -2 1 4 7 2 9 9 6 5 2 1 1 1 1 . 9 G T 2 2 0 9 + 5 3 8 2 2 9 3 9 5 3 5 3 2 3 7 . 4 + 8 4 + 7 0 C 1 6 4 3 6 4 1 1 . 3 ES-2 2 9 4 6 4 0 5 3 5 3 1 9 . 0 G T 2 2 1 8 + 5 7 9 2 2 18 2 5 5 7 5 9 5 5 3 . 5 + 3 4 8 ± 4 7 P N 1 0 4 + 0 . 1 P N 2 2 18 2 8 5 0 5 7 5 9 8 . 0 G T 2 2 2 6 + 5 8 9 2 2 2 6 2 3 5 8 5 8 8 2 . 9 + 1 2 7 + 3 8 M T + 6 0 3 5 5 2 . 2 -2 2 2 6 2 5 9 2 5 8 5 8 3 5 . 8 G T 2 2 5 3 + 5 8 2 2 2 5 3 2 9 5 8 12 5 5 5 . 0 + 6 5 5 ± 7 2 S 1 4 7 H I I 2 2 5 3 2 4 0 0 5 8 12 0 . 0 160 CHAPTER VII THE VARIABLE SOURCES Although the catalogue of compact sources i s a v a l u a b l e product of the survey o b s e r v a t i o n s , the primary concern of the survey r e l a t e s to the occurrence of v a r i a b i l i t y . Of the 807 sources i n c l u d e d i n the ca t a l o g u e , 23 are found to e x h i b i t s i g n i f i c a n t v a r i a t i o n s on e i t h e r the short or long term, and a f u r t h e r 18 are p o s s i b l y v a r i a b l e . The v a r i a b i l i t y i n d i c e s l i s t e d f o r each source i n t a b l e VII are a measure the s i g n i f i c a n c e of the observed v a r i a t i o n s a g a i n s t i n s t r u m e n t a l e f f e c t s , but, as such, they p r o v i d e l i t t l e i n f o r m a t i o n about the c h a r a c t e r of the v a r i a b i l i t y . T h i s chapter presents a summary of the r e s u l t s f o r the v a r i a b l e sources, and prov i d e s a b r i e f d e s c r i p t i o n of the o b s e r v a t i o n s obtained f o r each source, and the magnitude and time s c a l e of the observed v a r i a t i o n s . To provide an i n d i c a t i o n of the types of s i g n a l s produced by the short—term v a r i a b l e sources, f i g u r e s 41 and 42 show the scan t r a c e s , i n 1977, f o r the source producing the st r o n g e s t v a r i a b l e s i g n a l (GT0236+610), and the weakest s i g n a l (GT2134+536). The dates of the ob s e r v a t i o n s are i n d i c a t e d to the r i g h t of the scan t r a c e s . The outburst from GT0236+610, which reached a maximum f l u x d e n s i t y of 280 mJy on August 27, i s c l e a r l y evident near sample number 140 of the scans shown i n f i g u r e 41. The source i s very weak p r i o r to the outburst, dropping below the minimum d e t e c t a b l e l e v e l on a number of days. In f i g u r e 42, GT2134+536 can be seen around sample number 560 on the l a s t two days of o b s e r v a t i o n s . On August 29, 161 T 140 27o jjo 3?0 «?0 SMHPLE NO. s7o elo SMOOTHED om «c gure 41. Scans through the var iable source GT0236+610 in 1977. The date of each observation i s shown to the r i ght of each scan. The var iable source, s ituated near sample number 140, underwent an outburst that reached a maximum f lux density of 280 mJy on August 27. 1 62 - i — 70 mo - i — 210 — I 1 1— 280 350 420 SRHPLE NO. U90 S60 630 SMOOTHED OPTI MCC • 11 71 S I IS 77 3 t IS 77 3 • IS 77 3 • !7 77 S • I t 77 3 • IS 77 S U • 20 77 S • 21 77 S • 22 77 S • 23 77 S • 214 77 S • 2S 77 3 ( 2S 77 3 • 27 77 S r- • I i 77 S I 28 77 3 OECLI NATION ' Figure 42. Scans through the var iable source GT2134+536 in 1977. This i s the weakest var iable source detected. The source appears on the l a s t two days of observations near sample number 560. At maximum, on August 29, the f lux density i s 30 mJy. The non-var iable source at sample number 490 has a f l ux density of 100 mJy. 163 the f l u x d e n s i t y was a maximum of 30 mJy; having r i s e n from below the d e t e c t i o n l e v e l i n two days. Based on the survey o b s e r v a t i o n s alone, t h i s source was o r i g i n a l l y c l a s s e d as a p o s s i b l e v a r i a b l e . The v a r i a b i l i t y has been confirmed by a d d i t i o n a l o b s e r v a t i o n s made with the NRAO Very Large Array (Gregory and T a y l o r 1981). Table VIII l i s t s a l l of the v a r i a b l e sources d e t e c t e d i n the survey. Column 1 gives the source name, and columns 2 and 3 give the maximum and minimum observed f l u x d e n s i t y of the source. For sources that e x h i b i t no s i g n i f i c a n t short term v a r i a t i o n s , the f l u x d e n s i t i e s shown are an average over one observing s e s s i o n . In cases where the minimum f l u x d e n s i t y i s below the noise l e v e l an upper l i m i t i s p r o v i d e d . Column 4 g i v e s the t o t a l number of o b s e r v a t i o n s obtained f o r each source from a l l observing s e s s i o n s . The minimum time i n t e r v a l , i n days, between two c o n s e c u t i v e o b s e r v a t i o n s i s given in column 5. Column 6 g i v e s the minimum time i n t e r v a l over which s i g n i f i c a n t v a r i a t i o n was observed. P o s s i b l e v a r i a b l e s have not been i n c l u d e d i n t a b l e V I I I , s i n c e i t i s expected that a s u b s t a n t i a l f r a c t i o n of the sources in t h i s c l a s s are n o n - v a r i a b l e (see f i g u r e s 36 and 38). However, i t should be p o i n t e d out t h a t , except f o r strong sources, the term " p o s s i b l e v a r i a b l e " does not imply any s p e c i f i c , measured degree of s t a b i l i t y i n f l u x d e n s i t y . The measured f l u x d e n s i t y v a r i a t i o n s f o r p o s s i b l e v a r i a b l e s are at the l i m i t of what can be a t t r i b u t e d to noise and i n s t r u m e n t a l v a r i a t i o n s . T h i s l i m i t can be q u i t e l a r g e f o r weak sources. 164 Table VIII . The Var iable Sources Source Flux Density Max Min (mJy) No. Min. Sample Int. Min Var. Time Comments GT0026+627 60 <5 23 1 7d GT0045+643 1 40 50 7 1 Id flared on one day GT0106+612 490 230 23 1 i y poss. short term GT0116+622 70 18 22 1 i y GT0202+625 200 1 1 0 23 1 i y two sources GT0236+610 280 <5 44 1 1d B star, periodic GT0252+574 220 1 20 22 1 • i y GT0304+575 200 1 20 7 3 i y GT0314+565 360 240 6 3 i y GT0351+543a > 1 000 <5 8 1 1d trans ient GT0427+462 1 70 70 8 2 i y GT0459+415 300 1 60 6 6 1 3d GT0544+273 460 330 4 3 i y GT0554+242 1 200 900 5 2 2d GT0622+109 520 270 2 1 Y i y at end of scan GT1945+241 1 30 90 1 9 1 1d GT2000+287 40 <5 23 1 Id GT2100+468 450 320 8 1 3d GT2116+493 55 1 5 23 1 1d RS CVn ? GT2134+536 30 <5 24 1 Id GT2157+566 260 210 3 1 6 I6d GT2211+554 45 <10 24 1 i y GT2246+596 1 60 100 8 2 i y 1 65 Table IX. Possibly Var iable Sources Source Flux max Density min (mJy) No. Type GT0132+610 70 40 8 long-term GT0255+574 200 1 40 9 long-term GT0342+538 600 490 7 long-term GT0457+397 50 20 5 long-term GT0507+379 53 0 430 7 long-term GT0630+082 290 230 4 short-term GT1937+215 650 570 7 short-term GT1943+228 290 220 8 short-term GT1947+267 1 630 1 400 19 short-term GT1953+306 40 25 7 long-term GT1959+321 70 50 23 . long-term GT2111+494 40 <5 24 short-term GT2155+531 90 30 24 short-term GT2203+559 1 50 90 8 short-term GT2235+585 90 45 23 short-term GT2241+606 90 30 7 short-term GT2253+582 1 00 65 8 long-term GT2257+577 1 1 0 70 21 short-term $SIGNOFF 166 Consequently, some h i g h l y v a r i a b l e sources may be i n c l u d e d i n t h i s c l a s s . N e v e r t h e l e s s , more s e n s i t i v e o b s e r v a t i o n s are r e q u i r e d to c o n f i r m v a r i a b i l i t y among these sources. Table IX l i s t s the p o s s i b l e v a r i a b l e sources. The source name, maximum and minimum f l u x d e n s i t y , and number of observatons are given in columns 1 to 4. Column 5 i n d i c a t e s whether the p o s s i b l e v a r i a t i o n was observed on the short—term or long—term. In f i g u r e s 43 and 44 the f l u x d e n s i t i e s of the short—term v a r i a b l e s , and p o s s i b l e v a r i a b l e s , have been p l o t t e d as a f u n c t i o n of time. A b r i e f d e s c r i p t i o n of each of the v a r i a b l e source f o l l o w s . For some of the sources, follow-up o b s e r v a t i o n s have been c a r r i e d out at other o b s e r v a t o r i e s . In these cases, the r e s u l t s of the o b s e r v a t i o n s are i n c l u d e d . GT0026+627 Th i s source was observed f o r s i x t e e n days in 1977, d u r i n g which time only m a r g i n a l l y s i g n i f i c a n t v a r i a t i o n s were e x h i b i t e d . The mean f l u x d e n s i t y was 39 mJy. In 1978 a f u r t h e r f i v e o b s e r v a t i o n s were obtained. The source was d e t e c t e d at about 40 mJy on August 9, and, t h e r e a f t e r , decreased i n f l u x d e n s i t y to below the noise l i m i t of about 5 mJy on August 29. The source was not detected i n two scans c a r r i e d out in 1979. GT0045+643 No o b s e r v a t i o n s were obtained f o r t h i s source i n 1977. In 167 1978, the f l u x d e n s i t y f l a r e d to 140 mJy, from a quiescent l e v e l of about 60 mJy, on one day out of f i v e . For each of two ob s e r v a t i o n s i n 1979 a f l u x d e n s i t y of 50 mJy was measured. GT0106+612 T h i s source i s c l a s s e d as a p o s s i b l e short—term v a r i a b l e based on s i x t e e n o b s e r v a t i o n s i n 1977, which showed a decrease from a maximum f l u x d e n s i t y of 490 mJy on August 20, to a minimum of 420 mJy, on August 28. The source i s a d e f i n i t e long—term v a r i a b l e . The mean f l u x d e n s i t y decreased to 280 mJy in 1978, and, f u r t h e r , to 240 mJy i n 1979. However, no evidence f o r short—term v a r i a t i o n s was found in e i t h e r 1978 or 1 979. During the 1979 observing s e s s i o n , a simultaneous o b s e r v a t i o n at the Algonquin Radio Observatory (ARO) y i e l d e d a 10.5 GHz f l u x d e n s i t y of 270 mJy, i n d i c a t i n g a f l a t or r i s i n g continuum. In June of 1980, a m a r g i n a l l y s i g n i f i c a n t change in the 10.5 GHz f l u x d e n s i t y from 470 to 400 mJy, over a four day p e r i o d was observed. T h i s p r o v i d e s a d d i t i o n a l support f o r the p o s s i b l e short—term nature of the v a r i a b i l t y . Observations with the NRAO Very Large Array at 5 GHz show that the source i s unresolved to one arc-second. GT0116+622 In 1977 s i x t e e n o b s e r v a t i o n s were obtained of t h i s source y i e l d i n g a mean f l u x d e n s i t y of 18 mJy. No s i g n i f i c a n t v a r i a t i o n s were observed. However, at t h i s low f l u x d e n s i t y 168 l e v e l , v a r i a t i o n s are e a s i l y masked by r e c i e v e r n o i s e . In t h i s case short term v a r i a t i o n s with a one sigma l e v e l of l e s s than about 50% cannot be r u l e d out. Between 19.77 and 1978, the mean f l u x d e n s i t y i n c r e a s e d to 70 mJy. In 1979, the f l u x d e n s i t y had decreased to 35 mJy. GT0202+625 The s i g n a l from t h i s source appears to be a s u p e r p o s i t i o n of two sources, one with f l u x d e n s i t y of about 100 mJy and the other of a few ten's of mJy, separated by about four a r c -minutes i n d e c l i n a t i o n . The combined s i g n a l e x h i b i t s long term v a r i a t i o n s which have been a t t r i b u t e d to the stronger source. However, i t i s impossible to r u l e out v a r i a t i o n s i n the weaker component. No v a r i a t i o n s on the short term are e v i d e n t . The f l u x d e n s i t y i n c r e a s e d from 140 to 200 mJy between 1977 and 1978, and subsequently decreased to 110 mJy in 1979. GT0236+610 T h i s source e x h i b i t e d strong short term v a r i a t i o n s d u r i n g twelve days of ob s e r v a t i o n i n 1977. The f l u x d e n s i t y rose from l e s s than 5 mJy to 280 mJy over a p e r i o d of four days. During 1978 and 1979 observing s e s s i o n s , the source was observed once each day and s i m i l a r o u t b u r s t s were found. T h i s source has been proposed as the r a d i o c o u n t e r p a r t of the COS B gamma-ray source CG135+01 (Gregory and T a y l o r 1978). Since i t s d i s c o v e r y i n 1977, many follow-up o b s e r v a t i o n s 169 have been c a r r i e d out to e l u c i d a t e the nature of the source, and o b s e r v a t i o n s i n other wavelength regions (X-ray, UV, o p t i c a l ) have been made by other authors. An a c c u r a t e p o s i t i o n o b t ained with the VLA (Gregory et a l . 1979) has confirmed the i d e n t i f i c a t i o n with the B type s t a r l i s t e d i n t a b l e V I I I . Fu r t h e r a n a l y s i s of the survey r e s u l t s and of a d d i t i o n a l o b s e r v a t i o n s obtained at the ARO, show that the r a d i o emission from t h i s source i s p e r i o d i c , with a p e r i o d of 26.52 days (T a y l o r and Gregory 1982). A r e p r i n t of the l a t t e r paper, which a l s o presents a d i s c u s s i o n of the p r o p e r t i e s of the source in the context of a binary s t a r model, i s i n c l u d e d with t h i s t h e s i s i n the appendix. GT0252+574 Th i s source was observed f o r f i f t e e n days i n 1977 and showed no evidence f o r short term v a r i a t i o n s . Between 1977 and 1978, the f l u x d e n s i t y decreased from 220 mJy to 160 mJy and, by 1979, had f u r t h e r decreased to 120 mJy. During the 1979 observing s e s s i o n , a simultaneous o b s e r v a t i o n was c a r r i e d out at 5.0 GHz with the VLA. The measured f l u x d e n s i t y of 100 mJy i s s l i g h t l y lower than the survey r e s u l t , i n d i c a t i n g that a p o r t i o n (about 20%) of the f l u x may a r i s e from an extended component that i s unresolved at 3 arc-minute r e s o l u t i o n . GT0304+575 No o b s e r v a t i o n s of t h i s source were c a r r i e d out i n 1977. 170 Two observa t ions i n 1978, and a f u r t h e r f i v e i n 1979, showed no evidence for short—term v a r i a b i l i t y . However, the mean f l u x d e n s i t y decreased from 200 to 120 mJy between the two observ ing s e s s i o n s . GT0314+575 Thi s source was observed four times i n 1978 and twice i n 1979. No s i g n i f i c a n t shor t - te rm v a r i a t i o n s were found. Between 1978 and 1979, the mean f l u x d e n s i t y increased from 240 mJy to 360 mJy. GT0351+543a Thi s source was detected as a s t r o n g , t r a n s i e n t event . A f l a r e at a f l u x d e n s i t y greater than about 1 Jansky was observed on August 15, 1978. No source above the noise l e v e l was found at the scan p o s i t i o n of the f l a r e i n the average scan of the other four days of obse rva t ion i n 1978, or two days i n 1979. The event (which i s confirmed i n both r e c e i v e r s ) produced a response i n only one beam, i n d i c a t i n g an o f f s e t from the c e n t r a l t rack greater than about 2 a rc -minute s . Observat ions w i t h the VLA showed no source greater than 3 mJy w i t h i n 3' of the est imated p o s i t i o n of the f l a r e . GT0457+462 F i v e observa t ions of t h i s source i n 1978, and three i n 1979, show no evidence for short—term v a r i a t i o n s . The mean f l u x d e n s i t y decreased from 165 mJy i n 1978 to 70 mJy i n 1979. 171 GT0459+415 T h i s source was observed three times i n both 1978 and 1979. On each o c c a s i o n , a monotonic decrease i n f l u x d e n s i t y of about 30%, on a time s c a l e of about 20 days, was observed. The mean f l u x d e n s i t y was 270 mJy i n 1978 and 200 mJy i n 1979. In June, 1980, the 10.5 GHz f l u x d e n s i t y was measured at 360 mJy, which i s s i g n i f i c a n t l y higher than e i t h e r of p r e v i o u s l y measured 5 GHz f l u x d e n s i t i e s . T h i s suggests a r i s i n g continuum, although a c o r r e s p o n d i n g l y higher 5 GHz f l u x d e n s i t y , at the time of the o b s e r v a t i o n , cannot be r u l e d out. GT0554+273 T h i s source was observed once i n 1978, with a f l u x d e n s i t y of 460 mJy. In 1979, a f u r t h e r three o b s e r v a t i o n s were a b t a i n e d . No short—term v a r i a t i o n s were e v i d e n t , but the mean f l u x d e n s i t y had decreased to 330 mJy. GT0554+242 In 1978, t h i s source was observed four times. The f l u x d e n s i t y e x h i b i t e d a v a r i a t i o n of about 10% (from a maximum of 1040 mJy to a minimum or 900 mJy) over an i n t e r v a l of two days. In 1979, the source was observed once. The mean f l u x d e n s i t y had i n c r e a s e d to 1200 mJy. GT0622+109 Th i s source was observed only once i n both 1978 and 1979. Thus, no short—term v a r i a b i l i t y i n f o r m a t i o n i s a v a i l a b l e . 1 72 Between 1978 and 1979, the f l u x d e n s i t y i n c r e a s e d from 270 mJy to 520 mJy. I t should be noted, however, that the source i s s i t u a t e d very c l o s e to the end of a survey scan. T h e r e f o r e , although the v a r i a b i l i t y of the source s i g n a l between s e s s i o n s i s c l e a r , the i m p l i e d degree of v a r i a t i o n in the f l u x d e n s i t y should be accepted with some c a u t i o n . The p o s s i b i l i t y of b a s e l i n e e r r o r s augmenting the d i f f e r e n c e between the two s i g n a l s cannot be r u l e d out. GT1945+241 T h i s source was observed f o r nineteen days i n 1977. During t h i s time, the f l u x d e n s i t y v a r i e d from a minimum of 90 mJy to a maximum of 120 mJy, with s i g n i f i c a n t v a r i a t i o n s o c c u r r i n g on a time s c a l e of one day. No o b s e r v a t i o n s are a v a i l a b l e from e i t h e r 1978 or 1979. GT2000+287 T h i s source was observed f o r eighteen days in 1977. The f l u x d e n s i t y rose and f e l l a number of times d u r i n g t h i s p e r i o d . The v a r i a t i o n , from the maximum f l u x d e n s i t y of 30 mJy to l e s s than 5 mJy, occurred i n one day. The mean f l u x d e n s i t y over the eighteen days was 12 mJy. During 1978, the source was observed three times. Further f l u x d e n s i t y v a r i a t i o n s , between 40 mJy and 10 mJy, were found. The source was not detected in two scans c a r r i e d out in 1979. GT2116+493 1 73 T h i s source was d e t e c t e d i n a l l three o b s e r v i n g s e s s i o n s . In 1977, seventeen o b s e r v a t i o n s were obtained, y i e l d i n g a mean f l u x d e n s i t y of 25 mJy. V a r i a t i o n s o c c u r r e d on a time s c a l e of one day, from a maximum of 50 mJy to a minimum of 15 mJy. During four o b s e r v a t i o n s i n 1978, no v a r i a t i o n s were observed, however, the mean f l u x d e n s i t y had i n c r e a s e d to 55 mJy. In 1979, the source was observed twice at a constant l e v e l of 30 mJy. The source i s p o s i t i o n a l l y c o - i n c i d e n t with SAO 50694, an F8 s t a r with an apparent magnitude of about 11.5 (see t a b l e V I I I ) . T h i s source i s p o s s i b l y an RS CVn type b i n a r y . GT2134+536 Th i s source i s the weakest v a r i a b l e d e t e c t e d . During the l a s t 2 days of 18 o b s e r v a t i o n s i n 1977, the f l u x d e n s i t y i n c r e a s e d from l e s s than 5 mJy to 30 . The mean f l u x d e n s i t y over the 18 day p e r i o d was 10 mJy. No d e t e c t a b l e s i g n a l was d e t e c t e d d u r i n g 4 o b s e r v a t i o n s i n 1978, and 2 o b s e r v a t i o n s in 1979. T h i s source was o r i g i n a l l y c l a s s e d as a p o s s i b l e v a r i a b l e , based on the survey r e s u l t s . However, two o b s e r v a t i o n s at the VLA i n June and August of 1979, y i e l d e d f l u x d e n s i t i e s of 3.5±0.5 and 6.0±1.5 r e s p e c t i v e l y . These r e s u l t s are s i g n i f i c a n t l y lower than the 1977 f l u x d e n s i t y , and provide f u r t h e r evidence f o r v a r i a t i o n s on the short—term. GT2157+566 Th i s source was observed a t o t a l of three times; twice i n in 1978 and once in 1979. In 1978 the f l u x d e n s i t y changed 174 from 260 mJy to 210 mJy over the s i x t e e n days from August 13 to August 29. In 1979, a f l u x d e n s i t y of 215 mJy was measured. GT2211+554 T h i s source was observed eighteen times i n 1977. The mean f l u x d e n s i t y , i n that year, was 15 mJy. No short—term v a r i a t i o n s at a s i g n i f i c a n t l e v e l were e x h i b i t e d . Between 1977 and 1978, the mean f l u x d e n s i t y i n c r e a s e d to 45 mJy. The source was not det e c t e d i n two scans c a r r i e d out i n 1979. GT2246+596 No o b s e r v a t i o n s were obtained f o r t h i s source i n 1977. In s i x scans from 1978, the source was observed at a constant f l u x d e n s i t y of 160 mJy. Between 1978 and 1979, the mean f l u x d e n s i t y decreased to 100 mJy. 60-40-20 i i i i — i i i i — i i i i i — i — I — i I i — r — i — i — i — i — r — r 1 GT 0026+627 \ \ I S ° - } 6T0045+643 100- . ' 5 50+ 5O0|- . 5 GT0236+6I0 ~ 200h $ J ™ L . . . . i f f ff o h 5 f * f * 5 t CO S00|- } GT0459+4I5 O * 250h _ l U. I000r 900k 1 T 1 GT0554+242 I20J- » ^ 6TI945+24I 1 • • 1 • • • • • * • • • • • • • i i i 5 10 15 20 DAYS 3 0 1 J 1 - i i f } } . | » 1 { } f * } 6T2000+287 00- «} * 00-i GT2I00+468 } 40 -GT2I16*493 30- GT2134+536 6T2I57+566 0 0 ' 1 1 1 1 5 10 15 20 DAYS Figure 43. Flux density vs. time fo r the short-term variable sources. FLUX DENSITY (mJy) Li 177 CHAPTER VIII DISCUSSION 1 . Completeness L e v e l of the Survey E x c l u d i n g the three regions where g a l a c t i c c o n f u s i o n dominates, the f i r s t f i v e sequences of survey o b s e r v a t i o n s cover a s o l i d angle of about 0.08 s t e r a d i a n s . Within t h i s area, sources have been de t e c t e d down to f l u x d e n s i t i e s of 10-20 mJy. However, the f l u x d e n s i t y l e v e l at which the survey i s complete i s somewhat higher than t h i s . The primary l i m i t a t i o n on the completeness l e v e l a r i s e s from the decrease i n the e f f e c t i v e width of a scan with f l u x d e n s i t y . The l e v e l of completeness i s approximately given by the f l u x d e n s i t y at which the e f f e c t i v e scan width equarls the scan s e p a r a t i o n . The e f f e c t i v e width of a scan i s determined by the maximum o f f s e t at which a source can be d e t e c t e d . The l i m i t i n g f a c t o r i s the requirement that the weaker of the two beam responses produced by the source be g r e a t e r than twice <tj (see s e c t i o n IV 3.1). The minimum r e c e i v e r noise l e v e l ranges from 1-3 mk over the f i v e scan sequences, and the rms c o n f u s i o n s i g n a l from the e x t r a g a l a c t i c background l i e s between 2-3 mK. Thus, t a k i n g c i n the middle of the combined range, the 2c/j l i m i t i s , on the average, about 6.4 mK. For the median survey s e n s i t i v i t y of 0.67 K/Jy, the maximum o f f s e t (t9 m) at which a source with f l u x d e n s i t y S can be detected i s given by: g(© m)=9.6•S~ 1, where g (e ) i s the r e l a t i v e gain as a f u n c t i o n of o f f s e t of the beam f u r t h e s t from the source p o s i t i o n . The value of © m can be 178 c a l c u l a t e d f o r any f l u x d e n s i t y using the beam model (equation I I 1 . 1 ) . Over most of the survey r e g i o n , the East-West beam p r o f i l e i s approximately given by HPBW=2.8 and c=0.5 (see f i g u r e 8 ) . The e f f e c t i v e scan width W(s) versus f l u x d e n s i t y , f o r these values of the beam model parameters i s shown i n f i g u r e 45. For strong sources, W(s) i s about 4 arc-minutes. At low f l u x d e n s i t i e s the scan width r a p i d l y decreases to about 1 arc-minute at S=25 mJy. The c u r v e ' i n f i g u r e 45 does not extend below 20 mJy, because the e f f e c t i v e scan width i s small and i l l — d e f i n e d f o r S<15 mJy where, even at zero o f f s e t , the amplitude of one peak of the source s i g n a l i s comparable to the r e c e i v e r noise l e v e l . The s e p a r a t i o n between adjacent survey scans i s a f u n c t i o n of d e c l i n a t i o n , being a minimum of 2.3 arc-minutes at 6=62° and a maximum of 4.8 arc-minutes at 6=0°. However, the f r a c t i o n of scans at low d e c l i n a t i o n i s q u i t e s m a l l . About 75% of a l l the survey scans f a l l w i t h i n 10° of the median scan d e c l i n a t i o n of 57°. Thus, the scan s e p a r a t i o n of 2.6 arc-minutes, at t h i s d e c l i n a t i o n , i s r e p r e s e n t a t i v e of the survey o b s e r v a t i o n s . From f i g u r e 45, the e f f e c t i v e scan width equals 2.6 arc-minutes at a f l u x d e n s i t y of about 60 mJy . Taking i n t o c o n s i d e r a t i o n the e r r o r s on the c a l c u l a t i o n of W(s) (about 10% at t h i s f l u x d e n s i t y ) , a more c o n s e r v a t i v e estimate of the completeness l e v e l of the survey i s 70 mJy. At t h i s f l u x d e n s i t y , the s i g n a l l e v e l of the e n t i r e p r o f i l e i s l a r g e enough that the d e t e c t i o n p r o b a b i l i t y at © < © m i s e s s e n t i a l l y one (see f i g u r e 27) . 179 J £ 2 h o 3 'L < i i — i — i i i i 1 1 1 1 — i — i i i i i | j i i ' • « • l • « i i i • i 11 1 0 0 1 0 0 0 FLUX DENSITY (mJy) Figure45. The effective width of the survey scans as a function of flux density. 180 At lower f l u x d e n s i t i e s the completeness l e v e l r a p i d l y decreases. Based on f i g u r e 45, at 30 mJy, only about 50% of the sources w i t h i n the survey area are d e t e c t a b l e . The a c t u a l d e t e c t i o n e f f i c i e n c y i s expected to be somewhat lower than t h i s , s i n c e , at t h i s low l e v e l , the masking of source s i g n a l s by r e c e i v e r noise i s important at a l l values of the o f f s e t . 2. General P r o p e r t i e s of the Compact sources The catalogue of compact sources r e s u l t i n g from the survey o b s e r v a t i o n s r e p r e s e n t s the most s e n s i t i v e search f o r compact sources of r a d i o emission over a l a r g e p o r t i o n of the g a l a c t i c plane to date. A search of c a t a l o g u e s of o p t i c a l sources y i e l d s 29 p o s i t i o n a l c o - i n c i d e n c e s between the compact sources and g a l a c t i c o b j e c t s (see s e c t i o n VI 3.). O p t i c a l catalogues are r e s t r i c t e d to the o p t i c a l l y v i s i b l e p o r t i o n of the g a l a c t i c plane, w i t h i n a few kpc of the sun. Thus, even i f only a small p o r t i o n of the c o - i n c i d e n c e s represent a c t u a l p h y s i c a l a s s o c i a t i o n s , the r e s u l t s i n d i c a t e that a s u b s t a n t i a l f r a c t i o n of the compact sources are g a l a c t i c . Since the p o s s i b i l i t y e x i s t s that some of these sources represent new c l a s s e s of r a d i o source, i t i s of some i n t e r e s t to determine the s i z e of the g a l a c t i c component. Two approaches have been taken to estimate t h i s q u a n t i t y ; comparison of the number of d e t e c t i o n s to the r e s u l t s of e x t r a g a l a c t i c source counts, and examination of the d i s t r i b u t i o n of the r a d i o sources i n g a l a c t i c c o - o r d i n a t e s . 181 2.1 Number—Flux Density Relationship In order to compare the counts of the compact sources to extragalactic results, the t o t a l . s o l i d angle of the survey observations must be known. The calc u l a t i o n of th i s quantity is complicated by the change in the e f f e c t i v e scan width with flux density. For a scan width less than the minimum scan separation, the t o t a l s o l i d angle i s simply given by n(s)=L T-W(s), where L T is the t o t a l length of survey scans, after taking into account the overlap due to intersection of northbound and southbound scans. However, as the e f f e c t i v e scan width increases past the minimum scan separation, the variable amount of overlap between adjacent scans must also be accounted for. The t o t a l amount of overlap as a function of flux density was calculated by dividing the declination range of the survey into 5° bins. The t o t a l overlap i s then given by the expression: 0(s) =0.8-L T-l(W(s)-S(6j ) )-n(6j ) , (VIII.1) where n(6j) i s the number of scans in the i * h declination bin, and S(6j ) is the declination dependent separation of the scans. The factor of 0.8 is included since scans occur in sets of f i v e , with four overlap regions per set. The survey s o l i d angle as a function of flux density, n=Lj«W(s)-0.5-0(s), is shown in figure 46. At high flux densities,, the s o l i d angle slowly decreased from a maximum of 0.08 str to about 0.065 str at 100 mJy. Below 100 mJy, the s o l i d angle decreases more rapidly, to about 0.02 str at 25 mJy. Direct counts of extragalactic sources at 5 GHz, down to 182 1 1 1—i—I I i i | 1 1 1—I I I I I | 0.1 -.08-^ .06-To .04-.02-I I I i I I I I i I I I I I I l i l I 1 0 0 1 0 0 0 FLUX DENSITY (mJy) Figure 46 . The s o l i d angle of the survey observations as a function of f l u x density. 183 15 mJy, are summarized by Kellermann (1980). The d e n s i t y of sources i s w e l l represented down to 150 mJy by the simple power law N(>S)=60«S~ 1 5. At f l u x d e n s i t i e s l e s s than 150 mJy, the source d e n s i t y drops below t h i s r e l a t i o n s h i p to about 50% at 20 mJy. In f i g u r e 47, the e x t r a g a l a c t i c r e s u l t s are compared to the counts of survey sources. The q u a n t i t y p l o t t e d i s the r a t i o of the number of survey d e t e c t i o n s to the expected number of e x t r a g a l a c t i c d e t e c t i o n s , as a f u n c t i o n of f l u x d e n s i t y (AN(s)«n(s)). The e r r o r bars are the estimated one sigma u n c e r t a i n t i e s a r i s i n g from the e r r o r on the c a l c u l a t e d survey area, the u n c e r t a i n t y on the e x t r a g a l a c t i c source counts and the s t a t i s t i c a l N 0 5 e r r o r on the number of survey sources. At higher f l u x d e n s i t i e s (^ 80 mJy), a s l i g h t , constant excess over e x t r a g a l a c t i c counts i s i n d i c a t e d . However, the excess i s not s i g n i f i c a n t w i t h i n the estimated u n c e r t a i n t y . Thus, at higher f l u x d e n s i t i e s e x t r a g a l a c t i c sources can adequately account f o r the number of survey d e t e c t i o n s . Below about 60 mJy, a s i g n i f i c a n t excess, that i n c r e a s e s with d e c r e a s i n g f l u x d e n s i t y , i s e v i d e n t . T h i s p o p u l a t i o n of f a i n t sources i s taken to represent the g a l a c t i c component of the compact sources. The t o t a l number of expected e x t r a g a l a c t i c d e t e c t i o n s , down to 20 mJy, i s 560±20. I f the trend shown in f i g u r e 47 extends to lower f l u x d e n s i t i e s , about 50% of the 85 d e t e c t i o n s at 10—20 mJy are e x t r a g a l a c t i c . Thus, the t o t a l e x t r a g a l a c t i c c o n t r i b u t i o n to the catalogue of compact sources i s estimated to be 600±40, or 75±5% of the t o t a l c atalogue. It should be 184 T 1 1 1—I I I I | 1 1 1—I—I I I I | X UJ + + CO ' ' ' ' I I I I I ' ' I I I I I 1 1 0 0 1 0 0 0 FLUX DENSITY (mJy) F i gu re47 . The ratio of the number of survey sources to the expected number of extragalactic detections as a function of flux density. The error bars are the one sigma uncertainties. 185 noted that two of the areas of high g a l a c t i c c o n f u s i o n , excluded from the a n a l y s i s , correspond to d i r e c t i o n s i n which the l i n e of s i g h t i n t e r s e c t s a s u b s t a n t i a l p o r t i o n of a s p i r a l arm (Cygnus and Perseus arms). Since these regions have been excluded, the estimated g a l a c t i c component of approximately 200 of the f a i n t , compact sources l i k e l y r e presents an o v e r — a l l d i s k p o p u l a t i o n of r a d i o sources. Since the p o i n t of departure from the e x t r a g a l a c t i c counts at low f l u x d e n s i t i e s roughly corresponds to the "knee" in the s o l i d angle versus f l u x d e n s i t y curve i n f i g u r e 46, i t i s perhaps tempting to a t t r i b u t e the excess of f a i n t sources to systematic e r r o r i n the c a l c u l a t i o n of n ( s ) . Two f a c t s argue a g a i n s t t h i s i n t e r p r e t a t i o n . F i r s t , an estimate of the p o s s i b l e e r r o r on n(s) i s i n c l u d e d i n the e r r o r on the expected e x t r a g a l a c t i c c o n t r i b u t i o n . While e r r o r s as high as 10—20% are p o s s i b l e at low f l u x d e n s i t i e s , the 70% underestimation in n(s) r e q u i r e d to e x p l a i n the r e s u l t i s d i f f i c u l t to r e c o n c i l e with the p r e d i c t e d u n c e r t a i n t i e s . Second, the upper l i m i t s on the e x t r a g a l a c t i c component, based on the d i s t r i b u t i o n of the catalogue sources i n g a l a c t i c c o - o r d i n a t e s ( d i s c u s s e d i n the next s e c t i o n ) , r u l e out an e x t r a g a l a c t i c c o n t r i b u t i o n s i g n i f i c a n t l y g r e a t e r than 75%. Furthermore, s i n c e the e x t r a g a l a c t i c component i s c a l c u l a t e d s o l e l y on the b a s i s of the survey area, without t a k i n g i n t o account the smaller d e t e c t i o n e f f i c i e n c y at low s i g n a l to noise r a t i o (see f i g u r e 27), the e x t r a g a l a c t i c component i s s i g n i f i c a n t l y overestimated at low f l u x d e n s i t i e s . 186 2.2 D i s t r i b u t i o n i n G a l a c t i c Co-ordinates Since the i n c l i n a t i o n of the g a l a c t i c equator to a meridian of d e c l i n a t i o n changes along the g a l a c t i c plane, the g a l a c t i c l a t i t u d e l i m i t of the survey o b s e r v a t i o n s i s a f u n c t i o n of l o n g i t u d e (see f i g u r e 5). As a f u r t h e r consequence, the f r a c t i o n of a scan l o c a t e d w i t h i n a p a r t i c u l a r l a t i t u d e i n t e r v a l , Ab, a l s o v a r i e s with l o n g i t u d e . To o b t a i n the g a l a c t i c l a t i t u d e d i s t r i b u t i o n of the compact sources, the raw counts as a f u n c t i o n of l a t i t u d e must be c o r r e c t e d f o r these e f f e c t s . For a scan with endpoints at l a t i t u d e bj , the length of scan, (AL), w i t h i n the l a t i t u d e i n t e r v a l , Ab, i s : AL(bj) = (L.Ab)/(2-bj) , (VIII.2) where L i s the scan l e n g t h (4.3). Thus, l e t t i n g n (bj) be the number of scans ending at l a t i t u d e bj , the t o t a l l e n g t h of survey scan , L ( b j ) , w i t h i n the i n t e r v a l bj to bj+Ab, i s given by: L ( b j ) = Z n(b-)-AL(bj) . (VIII.3) The l a t i t u d e d i s t r i b u t i o n of survey sources was c a l c u l a t e d using a bin width of 0.1 degrees. Sources l o c a t e d l e s s than 6' from the end of the scan w i l l not be detected, because one peak of the source p r o f i l e i s not i n c l u d e d in the scan. T h e r e f o r e , in c a l c u l a t i n g n ( b j ) , the a c t u a l l a t i t u d e of the endpoint of each scan has been reduced by one bin width. The c o r r e c t e d l a t i t u d e d i s t r i b u t i o n of the compact sources, f o l d e d about the g a l a c t i c equator, i s shown i n f i g u r e 48. The o r d i n a t e i n the p l o t i s the number of sources d e t e c t e d 187 CP a> l . o> o> O i_ o a. u 3 O cn 0 5 1.0 1.5 2.0 Latitude (°) Figure 48. The galactic latitude distribution of the survey sources. The histogram is the number of sources detected per ' degree of scan length in each latitude bin. The expected extragalactic component is indicated by the dashed line. 188 per degree of the t o t a l survey scan l e n g t h l o c a t e d w i t h i n the l a t i t u d e b i n . E r r o r bars represent the N 0 5 s t a t i s t i c a l e r r o r on the number of sources i n each b i n . A d e f i n i t e decrease i n the source d e n s i t y i s evident at l a r g e r l a t i t u d e , which f u r t h e r i n d i c a t e s the presence of a s i g n i f i c a n t g a l a c t i c component. On the b a s i s of t h i s r e s u l t alone, a continued decrease i n the source d e n s i t y at higher l a t i t i u d e s cannot be r u l e d out, and, thus, only an upper l i m i t can be p l a c e d on an i s o t r o p i c c o n t r i b u t i o n from e x t r a g a l a c t i c sources. T h i s l i m i t i s 0.4 sources per degree, which corresponds to about 640 sources, or about 80% of the t o t a l c a t a l o g u e . T h i s r e s u l t i s c o n s i s t e n t with the e s t i m a t i o n of 75% based on the comparison to e x t r a g a l a c t i c source counts. The 75% l e v e l i s i n d i c a t e d by the dashed l i n e in f i g u r e 46. If t h i s value i s taken as a v a l i d r e p e s e n t a t i o n of the e x t r a g a l a c t i c c o n t r i b u t i o n , the mean d i s p e r s i o n of the g a l a c t i c component above the plane i s ~ 1 ° . From the l a t i t u d e l i m i t s of the survey as a f u n c t i o n of l o n g i t u d e ( f i g u r e 5), i t i s c l e a r that the data on source d e n s i t i e s at higher l a t i t u d e s comes mainly from the l o n g i t u d e region 100°<1<150°, where the m a j o r i t y of the survey o b s e r v a t i o n s occur. In t h i s l o n g i t u d e i n t e r v a l , the path l e n g t h to the edge of the galaxy l i e s roughly between 6 and 10 kpc. Thus, i f these sources are de t e c t e d out to the edge of the galaxy, the s c a l e - h e i g h t above the g a l a c t i c equator must be l e s s than 180 pc, which excludes g a l a c t i c o b j e c t s of p o p u l a t i o n type I I . Adopting the other p o i n t of view, f o r extreme p o p u l a t i o n I o b j e c t s , the minimum 189 observed s c a l e - h e i g h t i s ~40 pc (Guibert et a l . 1978). If t h i s i s taken as a lower l i m i t , f o r the g a l a c t i c source component, the mean d i s t a n c e to the r a d i o sources must be g r e a t e r than 2 kpc. The g a l a c t i c l o n g i t u d e d i s t r i b u t i o n of the survey sources i s shown in f i g u r e 49. In each 10° l o n g i t u d e i n t e r v a l , the number of d e t e c t i o n s normalized to the number of survey scans w i t h i n the same i n t e r v a l i s p l o t t e d . No attempt has been made to c o r r e c t f o r changes in e i t h e r the e f f e c t i v e width of the scans or the t e l e s c o p e s e n s i t i v i t y with l o n g i t u d e . Moreover, s i n c e an i s o t r o p i c component would produce a b a s e l i n e that v a r i e s with l o n g i t u d e with these e f f e c t s , the estimated 75% e x t r a g a l a c t i c c o n t r i b u t i o n (corresponding to an average of about 0.5 source per scan) has not been i n d i c a t e d . The two most conspicuous f e a t u r e s of the l o n g i t u d e p l o t are the r a p i d increase i n the number of sources d e t e c t e d per scan at 1<100° and the broad maximum extending from about 150° to 200°. The r i s e i n source d e n s i t y at low l o n g i t u d e , which occurs i n c o n t r a s t to the decrease in t e l e s c o p e s e n s i t i v i t y i n t h i s r e g i o n , may be a t t r i b u t e d to a higher r a t e of d e t e c t i o n of strong g a l a c t i c sources due to the i n c r e a s i n g path length of the l i n e of s i g h t through the g a l a c t i c plane. The excess source d e n s i t y between 150° and 200°, however, c o — i n c i d e s with the region of maximum te l e s c o p e s e n s i t i v i t y , which peaks at a l o n g i t u d e of about 170°. Thus, t h i s excess can be p a r t i a l l y , i f not wholly, e x p l a i n e d by a d d i t i o n a l d e t e c t i o n of weak sources due to i n c r e a s e d s e n s i t i v i t y , r a ther than an i n c r e a s e ini i i n m i iII II i i i I _2 II I II III I Mil I I I ! I I 201 c o u in %m a. u V. O to 1 1 60 80 100 120 140 Longitude 160 (°) 180 200 220 Figure 49 . The galactic longitude distribution of survey sources. The quantity plotted is the number of sources detected normalized to the number of scans in each longitude interval Also shown, at the top of the plot, are the longitudes of the variables and possible variables; short-term (upper section) and long-term (lower section). 191 in the source d e n s i t y i t s e l f . The number—flux d e n s i t y r e l a t i o n s h i p ( f i g u r e 47) i n d i c a t e s t h a t , as f l u x d e n s i t y decreases, more g a l a c t i c than e x t r a g a l a c t i c sources are d e t e c t e d . T h e r e f o r e , i t i s l i k e l y that the m a j o r i t y of the a d d i t i o n a l sources d e t e c t e d i n t h i s region are f a i n t g a l a c t i c sources. 2.3 The G a l a c t i c Component The comparison of the survey r e s u l t s to e x t r a g a l a c t i c source counts, and the d i s t r i b u t i o n of survey sources i n g a l a c t i c c o - o r d i n a t e s , i n d i c a t e the presence of a g a l a c t i c component numbering about 200 sources. In a d d i t i o n , the a n a l y s i s has r e v e a l e d three average p r o p e r t i e s of these sources; 1) f l u x d e n s i t y l e s s than about 60 mJy, 2) s c a l e — h e i g h t above the g a l a c t i c plane l e s s than 180 pc, and 3) average d i s t a n c e g r e a t e r than 2 kpc. We now c o n s i d e r what types of known g a l a c t i c r a d i o sources can e x p l a i n t h i s p o p u l a t i o n . Four types of g a l a c t i c sources are c o n s i d e r e d ; s t e l l a r winds from e a r l y type s t a r s , supernovae remnants, p l a n e t a r y nebulae and HII r e g i o n s . Very luminous s t a r s (M <-6) are known to have s t e l l a r winds with mass l o s s r a t e s ranging from 10~ 8 to 10~ 5 M 0/yr (Hutchings 1976; Conti and McCray 1980). Wright and Barlow (1975) have c a l c u l a t e d the r a d i o f l u x d e n s i t y a r i s i n g from thermal f r e e — f r e e emission i n the i o n i z e d gas of the wind. At 5 GHz, the f l u x d e n s i t y i s given by, S = 1 .6x1 0 8 • (M/v^ ) n / 3-D- 2 Jy, (VIII.4) 192 where M i s the mass l o s s r a t e i n M 0/yr, v„ i s the expansion v e l o c i t y of the wind in km/sec, and D i s the d i s t a n c e i n kpc. T y p i c a l expansion v e l o c i t i e s range from 100 to 1000 km/sec. Taking the most favourable case, M=10~5 and v o e = l00, to y i e l d a f l u x d e n s i t y g r e a t e r than 15 mJy the s t a r must be w i t h i n 2 kpc. At t h i s d i s t a n c e , a s t a r with M <-6 would have an apparent magnitude b r i g h t e r than 6, and would have been de t e c t e d i n the search f o r s t e l l a r p o s i t i o n c o — i n c i d e n c e s (see s e c t i o n V I . 3 ) . Furthermore, the maximum d i s t a n c e of 2 kpc i s below the lower l i m i t f o r the average d i s t a n c e of the g a l a c t i c sources. Thus, while i t i s p o s s i b l e , t a k i n g i n t o c o n s i d e r a t i o n the e x t i n c t i o n in the plane, that some of the b r i g h t e r s t a r s l i s t e d i n t a b l e VII are s t e l l a r wind sources, t h i s type of source cannot e x p l a i n the g a l a c t i c component of the survey sources. The s u r f a c e b r i g h t n e s s of supernova remnants decreases i n a w e l l d e f i n e d manner as the e j e c t e d m a t e r i a l expands with time. Clarke and Caswell (1976) show that at 408 MHz the f l u x d e n s i t y f o l l o w s the r e l a t i o n s h i p ; S ( 4 0 8 ) = ( 6 4 . 6 ) 3 - D - 3 . e - 1 Jy, (VIII.5) where © i s the angular diameter i n arc—minutes and D i s the d i s t a n c e i n kpc. Since supernovae remnants have t y p i c a l s p e c t r a l index c=-0.5, at 5 GHz, equation VI11.5 becomes, S(5OOO)=7.7x1O"-D- 3-0- 1 Jy. (VIII.6) To be d e t e c t e d by the survey, the angular diameter must be l e s s than 6 arc—minutes. However, at a d i s t a n c e of 10 kpc, a supernova remnant with e<6' has a f l u x d e n s i t y S>13 Jy; over an order of magnitude stronger than the t y p i c a l f l u x d e n s i t y of 193 the g a l a c t i c sources i n the c a t a l o g u e . Four of the survey sources are c o - i n c i d e n t with o p t i c a l l y known p l a n e t a r y nebulae. Cahn and Kal e r (1971) have c a l c u l a t e d that the l o c a l d e n s i t y of p l a n e t a r y nebulae i s 40 kpc" 3 . At t h i s d e n s i t y , about 250 p l a n e t a r y nebulae w i l l be w i t h i n the s o l i d angle of the survey f o r f l u x d e n s i t i e s l e s s than 60 mJy (see f i g u r e 44). Information about the r a d i o p r o p e r t i e s of p l a n e t a r y nebulae, as a c l a s s , i s mainly provided by Higgs (1973), who reported an i n v e s t i g a t i o n of the r a d i o s p e c t r a of 140 p l a n e t a r y nebulae. Radio l u m i n o s i t i e s vary c o n s i d e r a b l y from o b j e c t to o b j e c t , p r i m a r i l y as a r e s u l t of d i f f e r e n c e s i n e l e c t r o n d e n s i t y , which ranges from 20 cm"3 to 2x10" cm" 3. However, p l a n e t a r y nebulae are, i n ge n e r a l , much weaker than e i t h e r supernova remnants or HII r e g i o n s . The m a j o r i t y of p l a n e t a r y nebulae with known r a d i o f l u x d e n s i t i e s would be undetectable by the survey at d i s t a n c e s g r e a t e r than 2 kpc. Furthermore, the s c a l e — h e i g h t of p l a n e t a r y nebulae i s 260 pc, which i s c o n s i d e r a b l y l a r g e r 180 pc. Thus, while i t i s probable that a small f r a c t i o n of the g a l a c t i c sources are p l a n e t a r y nebulae, the major p o r t i o n of these sources remain unaccounted f o r . Current i n f o r m a t i o n of about the r a d i o p r o p e r t i e s of HII regions i s d e r i v e d from p r e v i o u s high frequency r a d i o continuum surveys of the g a l a c t i c plane, which, f o r l o n g i t u d e s greater than 60°, have been l i m i t e d to f l u x d e n s i t i e s g r e a t e r than 2 Jy. Among the sources d e t e c t e d , HII regions are i d e n t i f i e d by t h e i r thermal s p e c t r a ( A l t e n h o f f et a l . 1969), or the presence 1 94 of the Hl09a recombination l i n e ( R e i f e n s t e i n et a l . 1970). Based on these c h a r a c t e r i s t i c s , about 70% of the sources d e t e c t e d are a s s o c i a t e d with HII r e g i o n s . These HII regions can be d i v i d e d i n t o two c l a s s e s . In one c l a s s , are the d i s t a n t , h i g h l y luminous, so c a l l e d " g i a n t " HII r e g i o n s . The gi a n t HII r e g i o n s , which r e q u i r e a number of luminous s t a r s to f u r n i s h the energy needed to account f o r the q u a n t i t y of i o n i z e d gas observed, have t y p i c a l l y l a r g e l i n e a r diameters and e x h i b i t complex s t r u c t u r e . These sources are p r i m a r i l y c o n c e n t r a t e d i n a region 4—8 kpc from the g a l a c t i c c e n t e r . At gr e a t e r than 8 kpc (the minimum g a l a c t o — c e n t r i c d i s t a n c e of the survey r e g i o n ) , the surface d e n s i t y of g i a n t HII regions i s 0.1 kp c " 2 . T h e r e f o r e , only about 8 such sources are expected i n the survey r e g i o n . The second c l a s s of HII re g i o n s , d e t e c t e d by the e a r l i e r continuum surveys, are the i n t r i n s i c a l l y weaker, small HII re g i o n s , l o c a t e d w i t h i n a few kpc of the sun. Because of the high f l u x d e n s i t y l i m i t of e a r l i e r surveys, the sources d e t e c t e d , which number about 20 i n the 360 degrees around the sun, represent only the sample of high l u m i n o s i t y members of t h i s c l a s s . It i s , t h e r e f o r e , to be expected that more s e n s i t i v e o b s e r v a t i o n s w i l l r e v e a l a s i g n i f i c a n t number of small HII r e g i o n s . Some inf o r m a t i o n about the d i s t r i b u t i o n of these o b j e c t s , and a very rough lower l i m i t on the number d e n s i t y , i s provided by the o p t i c a l s t u d i e s of l o c a l HII r e g i o n s . The catalogue of o p t i c a l HII regions by Sharpless (1959) c o n t a i n s 313 o b j e c t s . 195 G e o r g e l i n et a l . (1979) d i s c u s s e s the space d i s t r i b u t i o n of 256 o p t i c a l HII regions f o r which d i s t a n c e s are known. The HII regions are w e l l d i s t r i b u t e d w i t h i n a region of about 4 kpc from the sun. If we take t h i s r e s u l t to be t y p i c a l of o p t i c a l HII r e g i o n s , the im p l i e d s u r f a c e d e n s i t y i s 6 k p c - 2 . Because of the e x t i n c t i o n i n the plane, the a c t u a l d e n s i t y of HII regions i s probably much higher than t h i s . However, adopting t h i s f i g u r e as a rough lower l i m i t , the s u r f a c e area of the galaxy covered by the survey o b s e r v a t i o n s , f o r f l u x d e n s i t i e s l e s s than 60 mJy, should c o n t a i n >300 HII r e g i o n s . Murdin and Shar p l e s s (1968) measured the s c a l e — h e i g h t of o p t i c a l HII regions to be 50 pc. T h i s i s w i t h i n the range of s c a l e — h e i g h t s compatable with the l a t i t u d e d i s t r i b u t i o n of the survey sources, and suggests a mean d i s t a n c e of 3 kpc. To be de t e c t e d at t h i s d i s t a n c e , a s i g n i f i c a n t f r a c t i o n of the HII regions must have r a d i o l u m i n o s i t y g r e a t e r than 5x10 3 1 e r g s / s e c . In summary, s t e l l a r winds from e a r l y type s t a r s , and the m a j o r i t y of p l a n e t a r y nebulae are too weak to be d e t e c t a b l e at d i s t a n c e s g r e a t e r than 2 kpc. Supernova remnants, with angular diameter small enough to be d e t e c t a b l e by the survey, have f l u x d e n s i t y much stronger than the g a l a c t i c survey sources. Small HII regions are s u f f i c i e n t l y numerous to e x p l a i n the g a l a c t i c component. Furthermore, the measured s c a l e — h e i g h t of o p t i c a l HII regions, matches the l a t i t i u d e d i s t r i b u t i o n of the survey sources for a mean d i s t a n c e of 3 kpc, which i s the t y p i c a l half—way point to the edge of the galaxy f o r most of the survey 196 r e g i o n . Thus, i t i s probable that most, i f not a l l , of the f a i n t g a l a c t i c survey sources are a s s o c i a t e d with small HII r e g i o n s . To check t h i s c o n c l u s i o n , f u r t h e r , s e n s i t i v e o b s e r v a t i o n s at other f r e q u e n c i e s , to measure the s p e c t r a of these sources, are r e q u i r e d . 3. The V a r i a b l e Sources T h i s survey has attempted to determine the i n c i d e n c e of v a r i a b i l i t y among c e l e s t i a l r a d i o sources, at centimeter wavelengths, i n as unbiased a f a s h i o n as p o s s i b l e . . U n l i k e e a r l i e r searches f o r v a r i a b i l i t y , no i n i t i a l s e l e c t i o n c r i t e r i a have been adopted that c o n s t r a i n the o b s e r v a t i o n s to a s p e c i f i c c l a s s of source. Instead, the survey o b s e r v a t i o n s are combined to y i e l d a s e n s i t i v e l i s t of compact r a d i o sources that provide the data base f o r the v a r i a b i l t i y search. Thus, the only p r e r e q u i s i t e f o r i n c l u s i o n in the v a r i a b i l i t y search i s that a r a d i o source produce a d e t e c t a b l e s i g n a l i n the average of a number of repeated o b s e r v a t i o n s of a given area of the sky. T h i s requirement does, however, introduce an o b s e r v a t i o n a l s e l e c t i o n e f f e c t at low f l u x d e n s i t i e s . Since the s i g n a l to noise of a source present, say, on only one day of the ob s e r v a t i o n s decreases with the number of days averaged, f o r f l u x d e n s i t i e s c l o s e to the noise l e v e l , the p r e r e q u i s i t e of d e t e c t i o n tends to b i a s the o b s e r v a t i o n s toward sources that produce a d e t e c t a b l e s i g n a l i n a l l of the o b s e r v a t i o n s . Thus, while the o v e r — a l l s e n s i t i v i t y of the survey i s s u b s t a n t i a l l y improved by averaging the o b s e r v a t i o n s , weak t r a n s i e n t events 197 are hidden by t h i s technique. The mean noise l e v e l of the o b s e r v a t i o n s i s 2 mk i n the average scan, which i s t y p i c a l l y c o n s t r u c t e d from a combination of s i x o b s e r v a t i o n s . A source present on only one day out of s i x , must reach a l e v e l of 70 mJy, or higher, to produce a s i g n a l i n the average scan with g r e a t e r than 50% p r o b a b i l i t y of d e t e c t i o n . In 1977, with 20 repeated o b s e r v a t i o n s , t h i s l e v e l i s 110 mJy. In c o n t r a s t , i n s e a r c h i n g a s i n g l e o b s e r v a t i o n (one scan) fo r compact sources, the 50% d e t e c t i o n p r o b a b i l i t y l e v e l i s 25 mJy. A search f o r t r a n s i e n t events w i l l be c a r r i e d out at a l a t e r date, by independently a n a l y s i n g each days o b s e r v a t i o n s . More than 80% of the catalogue sources have f l u x d e n s i t y l e s s than 100 mJy, and more than 60%, l e s s than 40 mJy. The * d e t e c t i o n of short—term v a r i a t i o n s i s l i m i t e d by r e c e i v e r noise to a one sigma l e v e l of 15 mJy, roughly corresponding to peak to peak v a r i a t i o n s of 30—40 mJy. Thus, for the m a j o r i t y of the sources, l u m i n o s i t y v a r i a t i o n s of the order of 100% are r e q u i r e d f o r v a r i a b i l i t y to be d e t e c t e d . The s i t u a t i o n i s s i m i l a r f o r long—term v a r i a t i o n s . The lower l i m i t on d e t e c t a b l e v a r i a t i o n s reaches 100% at about 80 mJy (see equation V.6). T h e r e f o r e , t h i s survey p r o v i d e s l i t t l e i n f o r m a t i o n about f r a c t i o n a l v a r i a t i o n s of low i n t r i n s i c amplitude. Of the 807 compact sources d e t e c t e d in the survey r e g i o n , 23 are found to be c l e a r l y v a r i a b l e , and a f u r t h e r 18 are c l a s s e d as p o s s i b l y v a r i a b l e . None of these sources were p r e v i o u s l y known. The v a r i a b l e s and p o s s i b l e v a r i a b l e s have 198 been c l a s s i f i e d i n t o two types; short—term and long—term, a c c o r d i n g to the time s c a l e of the observed v a r i a t i o n s . A number of the sources were measured to be v a r i a b l e on both time s c a l e s . However, while short—term v a r i a b l e s are a l s o l i k e l y to be measured as v a r i a b l e on the long—term, the reverse i s not t r u e . Thus, a source i s c l a s s e d as a long—term v a r i a b l e only i f no short term v a r i a t i o n s were det e c t e d . Based on t h i s Scheme, 12 of the v a r i a b l e sources are short—term v a r i a b l e s , and 11 are long—term v a r i a b l e s . Among the p o s s i b l y v a r i a b l e sources, 10 are short—term and 8 are long—term. Because of the l i m i t a t i o n of measurable long—term v a r i a t i o n s to stronger sources, 9 of the 11 long—term v a r i a b l e s have f l u x d e n s i t y g r e a t e r than 100 mJy. Thus, in most cases, the upper l i m i t on short—term v a r i a b i l i t y f o r t h i s c l a s s of sources i s comparatively low, about 10%-20%. However, one of the long—term v a r i a b l e s i s a p o s s i b l e short—term v a r i a b l e (GTO106+612). T h i s r a i s e s the q u e s t i o n ; are long—term v a r i a b l e s a d i s t i n c t c l a s s from short—term v a r i a b l e s ? To determine whether long—term v a r i a b l e s are more l i k e l y to e x h i b i t short—term v a r i a t i o n s , at a low l e v e l , than sources c l a s s e d n o n — v a r i a b l e on the long—term; the short—term i n d i c e s , V, and V 2, f o r the long—term v a r i a b l e s , were compared to the d i s t r i b u t i o n of short—term i n d i c e s f o r a l l sources c l a s s e d n o n — v a r i a b l e having f l u x d e n s i t y greater than 100 mJy. No s i g n i f i c a n t d i f f e r e n c e was found. The short—term i n d i c e s f o r the long—term v a r i a b l e s e x h i b i t a s c a t t e r more or l e s s , u n i f o r m l y about the mean values f o r n o n - v a r i a b l e sources, and, 199 with the exception of GT0106+612, none d e v i a t e by more than two standard d e v i a t i o n s from the means. Thus, i n g e n e r a l , there appears to be no l i n k between long—term and short—term v a r i a b i l t i y . For each of the v a r i a b l e and p o s s i b l y v a r i a b l e sources, the r a t i o Rv=Smax/Smin has been c a l c u l a t e d . In f i g u r e 50, the d i s t r i b u t i o n of R v f o r these sources i s shown. To accommodate l a r g e values of R v, a l o g a r i t h m i c s c a l e has been used, and bin widths f o r the histograms have been adj u s t e d to produce equal widths on a l o g a r i t h m i c s c a l e . The r e s u l t s f o r long—term and short—term v a r i a b l e s have been p l o t t e d s e p a r a t e l y . For the long—term v a r i a b l e s , the number of sources decreases r a p i d l y as R v i n c r e a s e s . E i g h t y percent have R v l e s s than 2.3, and no sources have R v g r e a t e r than 5. I t i s i n t e r e s t i n g to compare t h i s r e s u l t to v a r i a t i o n s observed from e x t r a g a l a c t i c sources. At 2.7 GHz, Kesteven et a l . (1977) f i n d an upper l i m i t on the f r a c t i o n a l v a r i a t i o n s (AS/2-S) of e x t r a g a l a c t i c sources of 0.4, which corresponds to R v=2.3. Based on a comparison of v a r i a b i l i t y amplitudes at 2.8 and 4.5 cm, Andrew et a l . (1978) c a l c u l a t e a frequency dependence v 0 A . The r e s u l t of Kesteven et a l . , e x t r a p o l a t e d to 5 GHz, i m p l i e s as upper l i m i t from the known types of e x t r a g a l a c t i c v a r i a b l e s of R v~3, which i s s i m i l a r to the present r e s u l t f o r long-term v a r i a b i l i t y . Thus, long—term v a r i a t i o n s do not d i f f e r s i g n i f i c a n t l y from the known p r o p e r t i e s of e x t r a g a l a c t i c r a d i o sources. The d i s t r i b u t i o n of R v f o r short—term v a r i a t i o n s i s broader, and extends to much higher values, than the long—term 200 T 1 1 I I I T 1 1 1—I I I 1 0 o k-z> o to Short-term Long-term S>5\ Si E 3 Z L - . 4 - — J • ' 1 I I III 1 0 5 0 1 0 0 Figure 50. The d i s t r i bu t i on of R (S m a x/S . ). for the var iable and possibly var iable sources. The dashed histogram shows the d i s t r i bu t i on for short-term var iab les , and the s o l i d l i n e fo r long-term var iables. 201 r e s u l t s . If we d e f i n e a source with R v>5 as h i g h l y v a r i a b l e , then 26% of the short-term v a r i a t i o n s are i n t h i s c l a s s . I t i s noteworthy t h a t , i n s p i t e of the f a c t that 20 repeated o b s e r v a t i o n s were obtained f o r only 20% of the survey r e g i o n , f i v e of the s i x h i g h l y v a r i a b l e r e s u l t s were obtained from scans observed more than 20 times. T h i s r e s u l t i m p l i e s that the p r o b a b i l i t y of d e t e c t i n g h i g h l y v a r i a b l e emission i n c r e a s e s with the number of repeated o b s e r v a t i o n s of of a given region of the sky. T h i s , i n t u r n , suggests that h i g h l y v a r i a b l e sources spend a s i g n i f i c a n t f r a c t i o n of the time in a quiescent s t a t e . As mentioned, due to measurement l i m i t a t i o n s , the m a j o r i t y of the long—term v a r i a b l e s have mean f l u x d e n s i t y g r e a t e r than 100 mJy. In view of the i n d i c a t e d higher p r o p o r t i o n of e x t r a g a l a c t i c sources among the stronger survey sources, and of the s i m i l a r i t y of the d i s t r i b u t i o n of long—term v a r i a b i l i t y amplitudes to e x t r a g a l a c t i c r e s u l t s , i t i s probable that the m a j o r i t y of these sources are e x t r a g a l a c t i c . By the same token, based on past experience, i t i s probable that most, i f not a l l , of the short—term v a r i a b l e s are g a l a c t i c . The g a l a c t i c l o n g i t u d e s of the v a r i a b l e s and p o s s i b l e v a r i a b l e s are shown by the short v e r t i c a l bars i n the upper p o r t i o n of f i g u r e 46. The r e s u l t s are d i v i d e d a c c o r d i n g to v a r i a b i l i t y time s c a l e ; short—term i s shown on the top, and long—term underneath. The hi g h e s t c o n c e n t r a t i o n of long—term v a r i a b l e s occurs in the lo n g i t u d e region 120°—150°. T h i s region i s a l s o the area of the highest c o n c e n t r a t i o n of survey o b s e r v a t i o n s , 202 and the d i s t r i b u t i o n i s c o n s i s t e n t with a f a i r l y uniform d i s t r i b u t i o n of long—term v a r i a b l e s , which i s expected f o r e x t r a g a l a c t i c sources. The suggestion of a s l i g h t c o n c e n t r a t i o n toward lower l o n g i t u d e s , f o r the short—term v a r i a b l e s , supports the p r o b a b i l i t y that these sources are g a l a c t i c . If t h i s i s the case, then the twelve v a r i a b l e s d e t e c t e d represent an in c r e a s e of 50% i n the number of known, v a r i a b l e , g a l a c t i c r a d i o sources, and, i f the p o s s i b l e v a r i a b l e s are i n c l u d e d , the i n c r e a s e approaches 100%. I f , on the other hand, any of the short—term, h i g h l y v a r i a b l e sources are e x t r a g a l a c t i c , t h i s would provide the f i r s t c l e a r evidence of t h i s degree of v a r i a b i l i t y from an e x t r a g a l a c t i c o b j e c t . It i s c l e a r l y important to c a r r y out f u r t h e r o b s e r v a t i o n s of these v a r i a b l e sources to determine t h e i r o r i g i n s . Assuming, f o r the moment, that the short—term v a r i a b l e s are g a l a c t i c , the number de t e c t e d represent about 5% of the t o t a l estimated g a l a c t i c component of about 200 sources. Because d e t e c t i o n s are, in g e n e r a l , b i a s e d towards high l u m i n o s i t y v a r i a b l e s , t h i s f i g u r e should s i g n i f i c a n t l y underestimate the true i n c i d e n c e of h i g h l y v a r i a b l e r a d i o emission among g a l a c t i c sources. For example, i f the maximum observed r a d i o l u m i n o s i t y of 1 0 2 9 e r g s — s " 1 from RS CVn b i n a r i e s i s , i n f a c t , a p h y s i c a l l i m i t f o r t h i s c l a s s of source, f o r a minimum d e t e c t a b l e f l u x d e n s i t y of 20 mJy, an RS CVn c o u l d not be detected at d i s t a n c e s g r e a t e r than about 300 pc. Furthermore, f o r the minimum d e t e c t a b l e v a r i a t i o n of about 40 mJy, such a source would not be c l a s s e d as v a r i a b l e at a 203 d i s t a n c e g r e a t e r than 200 pc. At 1 kpc, the minimum d e t e c t a b l e v a r i a b l e l u m i n o s i t y i s about 10 3° e r g s — s _ 1 . Over the l o n g i t u d e coverage of the survey, the path l e n g t h through the g a l a c t i c plane v a r i e s from 5-18 kpc. Thus, over the p o r t i o n of the g a l a c t i c plane i n c l u d e d i n the survey o b s e r v a t i o n s , coverage of the galaxy i s complete only f o r a c l a s s of sources with v a r i a b l e l u m i n o s i t y g r e a t e r than about 1 0 3 2 — 1 0 3 3 e r g s — s " 1 . Three of the p r e v i o u s l y known g a l a c t i c v a r i a b l e s have l u m i n o s i t y at l e a s t t h i s high (Cyg X—3, C i r X-1 and SS 433) and a l l are members of the strong X—ray c l a s s of v a r i a b l e source. The s i z e of the path l e n g t h through the g a l a c t i c plane at the l o n g i t u d e of each source a l l o w s an upper l i m i t to be p l a c e d on the v a r i a b l e r a d i o l u m i n o s i t y , i f the source i s l o c a t e d i n s i d e the galaxy. The t y p i c a l upper l i m i t i s a few 10 3" e r g s — s " 1 . Only in the case of GT2000+288 and the t r a n s i e n t GT0351+543 does the upper l i m i t exceed 1 0 3 5 e r g s — s " 1 . Therefore, i f these sources are spread more or l e s s u niformly throughout the galaxy, so that most are at d i s t a n c e s g r e a t e r than one kpc, the v a r i a b l e l u m i n o s i t y i n most cases i s between 10 3° and 1 0 3 5 e r g s — s _ 1 , and the t y p i c a l l u m i n o s i t y probably l i e s near the center of t h i s range, at 1 0 3 2 e r g s — s " 1 . Two of the short-term v a r i a b l e s , GT0236+610 and GT2116+493, were found to be p o s i t i o n a l l y c o - i n c i d e n t with s t e l l a r o b j e c t s . The a s s o c i a t i o n of GT0236+610 with the BO s t a r (LS I +61°303) has been confirmed through an accurate r a d i o p o s i t i o n obtained with the NRAO Very Large Array (Gregory 204 et a l . 1979). The d i s t a n c e of 2.3 kpc, i n f e r r e d from a s s o c i a t i o n with the HII reg i o n , IC 1805, i m p l i e s a r a d i o l u m i n o s i t y of 1 0 3 2 e r g s - s " 1 . Further o b s e r v a t i o n s of GT0236+610 have r e v e a l e d a number of unique p r o p e r t i e s . The source has been proposed as the r a d i o co u n t e r p a r t of the COS B r—r a y source CG135+01 (Gregory and T a y l o r 1978), and a d d i t i o n a l a n a l y s i s of the COS B data ( P o l l o c k et a l . 1980) f u r t h e r supports the i d e n t i f i c a t i o n . The o b j e c t i s a confirmed X—ray source (Share et a l . 1978; Bignami et a l . 1980). The r a d i o emission has been shown to be p e r i o d i c (Taylor and Gregory 1982), with a p e r i o d of 26.52 days. Ext e n s i v e o p t i c a l and u l t r a — v i o l e t o b s e r v a t i o n s (Hutchings and Crampton 1981) r e v e a l r a d i a l v e l o c i t y v a r i a t i o n s c o n s i s t e n t with the r a d i o p e r i o d , and show that LS I +61°303 i s a B0—B0.5 main sequence s t a r that i s r o t a t i n g r a p i d l y and l o s i n g mass i n the e q u a t o r i a l r e g i o n . Although these combined p r o p e r t i e s are unique among known o b j e c t s , the high r a d i o and X—ray l u m i n o s i t y , and the bin a r y nature of t h i s source, p l a c e s i t among the strong X—ray b i n a r y c l a s s of v a r i a b l e r a d i o source. A more d e t a i l e d d i s c u s s i o n of the p r o p e r t i e s of t h i s p e c u l i a r object i s pro v i d e d i n the appendix i n c l u d e d with the t h e s i s . No a d d i t i o n a l o b s e r v a t i o n s are a v a i l a b l e f o r GT2116+493. Thus, i n t h i s case, the p o s s i b l e a s s o c i a t i o n remains open to q u e s t i o n . N e v e r t h e l e s s , i t i s noteworthy, that the s p e c t r a l type of the c o - i n c i d e n t s t a r i s w i t h i n the range of the RS CVn type b i n a r y s t a r s . For a normal F8 main sequence s t a r of 205 a b s o l u t e magnitude +4, the apparent magnitude of 11.5 i m p l i e s a d i s t a n c e of about 300 pc. At t h i s d i s t a n c e , the maximum observed f l u x d e n s i t y of 50 mJy corresponds to a l u m i n o s i t y of ~5x10 2 9 e r g s — s " 1 . T h i s i s somewhat high compared to the known RS CVn's. However, in view of the very rough nature of the c a l c u l a t i o n , the d i s c r e p a n c y i s not s i g n i f i c a n t . T h e r e f o r e , the p r e s e n t l y known combined r a d i o and o p t i c a l p r o p e r t i e s of GT2116+493, and the c o - i n c i d e n t s t a r , are c o n s i s t e n t with an RS CVn type b i n a r y system. Fur t h e r o b s e r v a t i o n s are r e q u i r e d to e i t h e r c o n f i r m or r u l e out t h i s i n t e r p r e t a t i o n . No o p t i c a l c o u n t e r p a r t s were found f o r the other v a r i a b l e sources. The search i s l i m i t e d to o b j e c t s b r i g h t e r than about 12 t h magnitude. Thus, while RS CVn's can be f o r the most part r u l e d out f o r the other short—term v a r i a b l e s , a deeper o p t i c a l search may y i e l d f u r t h e r i d e n t i f i c a t i o n s . However, s i n c e the number d e n s i t y of s t a r s i n c r e a s e s r a p i d l y at f a i n t e r magnitudes, more accurate r a d i o p o s i t i o n s are r e q u i r e d before c a r r y i n g out such a search. 206 CHAPTER IX SUMMARY AND CONCLUSIONS Th i s t h e s i s presented the f i r s t r e s u l t s of a survey of the g a l a c t i c plane f o r sources of v a r i a b l e r a d i o emission. Previous searches f o r v a r i a b l e sources have e n t a i l e d c o n s i d e r a b l e s e l e c t i o n b i a s . For e x t r a g a l a c t i c sources, t h i s b i a s i s toward more s t a b l e sources, and, f o r g a l a c t i c sources, the search has been l i m i t e d to s p e c i f i c c l a s s e s of o p t i c a l o b j e c t s . By making repeated o b s e r v a t i o n s of the e n t i r e survey r e g i o n , t h i s survey attempts to overcome these l i m i t a t i o n s and, thus, address the q u e s t i o n of v a r i a b i l i t y in as unbiased a f a s h i o n as p o s s i b l e . An a n a l y s i s of the f i r s t 40% of the data has r e s u l t e d i n the d e t e c t i o n of 807 compact r a d i o sources. Short—term v a r i a b i l i t y i s determined by measuring the s i g n a l s t r e n g t h of each source i n repeated o b s e r v a t i o n s d u r i n g one observing s e s s i o n , using a c r o s s — c o r r e l a t i o n technique. Long—term v a r i a t i o n s are measured by comparing mean source s t r e n g t h s between two observing s e s s i o n s . For strong sources, the lower l i m i t on d e t e c t a b l e v a r i a t i o n s i s 10% f o r short—term v a r i a t i o n s and 16% f o r long—term v a r i a t i o n s . However, because the m a j o r i t y of the detected sources have f l u x d e n s i t y l e s s than 100 mJy, i n g e n e r a l , v a r i a b i l i t y d e t e c t i o n i s l i m i t e d to higher f r a c t i o n a l v a r i a t i o n s . At 100 mJy, the v a r i a b i l i t y d e t e c t i o n l i m i t i s 40% f o r short—term v a r i a t i o n s and 70% f o r long—term v a r i a t i o n s . Short—term v a r i a b i l t i y i n f o r m a t i o n i s a v a i l a b l e for 758 of the compact sources, and long—term v a r i a b i l i t y 207 i n f o r m a t i o n f o r 434 sources. The r e s u l t s are presented i n the form of a catalogue of compact sources, i n c l u d i n g an index of the v a r i a b i l i t y of each source. A comparison of the number—flux d e n s i t y r e l a t i o n s h i p of the 807 survey d e t e c t i o n s , to e x t r a g a l a c t i c source counts, and the d i s t r i b u t i o n of the sources i n g a l a c t i c c o - o r d i n a t e s , i n d i c a t e s that > 25% (200) of the catalogue sources are g a l a c t i c . These g a l a c t i c sources have the f o l l o w i n g p r o p e r t i e s ; 1) f l u x d e n s i t y l e s s than about 60 mJy, 2) s c a l e — h e i g h t above the g a l a c t i c plane l e s s than 180 pc, 3) average d i s t a n c e g r e a t e r than 2 kpc. I t i s concluded that the m a j o r i t y of the n o n — v a r i a b l e , g a l a c t i c sources are small HII regions w i t h i n about 6 kpc of the sun. Twenty—three, newly d i s c o v e r e d v a r i a b l e sources are i n c l u d e d i n the catalogue; 12 short—term v a r i a b l e s and 11 long—term v a r i a b l e s . In a d d i t i o n , 18 sources are c l a s s e d as p o s s i b l y v a r i a b l e . The l o n g i t u d e d i s t r i b u t i o n of the v a r i a b l e s , and p o s s i b l e v a r i a b l e s , suggests that most, i f not a l l , of the long—term v a r i a b l e s are e x t r a g a l a c t i c , and the short—term v a r i a b l e s are p r i m a r i l y g a l a c t i c . The observed f r a c t i o n a l v a r i a b i l i t y of the long—term v a r i a b l e s does not d i f f e r s i g n i f i c a n t l y from that of known e x t r a g a l a c t i c v a r i a b l e sources. Among the short—term v a r i a b l e s , 26% (6 sources) have f r a c t i o n a l amplitude g r e a t e r than the upper l i m i t on known e x t r a g a l a t i c v a r i a b l e s . These sources have been termed h i g h l y v a r i a b l e . While t h i s r e s u l t i s not unusual, i f these sources are g a l a c t i c , the p o s s i b i l i t y that some are e x t r a g a l a c t i c 208 cannot be r u l e d out at t h i s stage. F i v e of the s i x h i g h l y v a r i a b l e sources were detected i n the 20% of the survey region f o r which a l a r g e number of repeated o b s e r v a t i o n s were c a r r i e d out. T h i s f a c t i m p l i e s that the p r o b a b i l i t y of d e t e c t i n g h i g h l y v a r i a b l e emission i n c r e a s e s with the number of repeated o b s e r v a t i o n s of a given region of the sky, which suggests that h i g h l y v a r i a b l e sources are quie s c e n t f o r a s i g n i f i c a n t f r a c t i o n of the time. Two of the short—term, h i g h l y v a r i a b l e sources (GT0236+610 and GT2116+493) are p o s i t i o n a l l y c o — i n c i d e n t , to w i t h i n the e r r o r on the survey c o - o r d i n a t e s , with s t e l l a r o b j e c t s b r i g h t e r than 12 magnitude. One of the a s s o c i a t i o n s (GT0236+610) has s i n c e been confirmed. The r a d i o emission from t h i s o b j e c t i s p e r i o d i c , with a p e r i o d of 26.52 days. With the exception of p u l s a r s , only one other o b j e c t i s known to e x h i b i t p e r i o d i c r a d i o emission ( C i r X—1, P=16.59 days). I t i s noteworthy, that GT0236+610 i s the f i r s t source shown to be p e r i o d i c as a r e s u l t of r a d i o o b s e r v a t i o n s . For the other a s s o c i a t i o n , GT2116+493, the combined p r o p e r t i e s of the r a d i o sources, and the c o — i n c i d e n t s t a r , are c o n s i s t e n t with an RS CVn type b i n a r y system, at a d i s t a n c e of about 300 pc. If the remaining short—term v a r i a b l e s are g a l a c t i c , t h e i r l u m i n o s i t i e s l i e w i t h i n the range 1 0 3 0—1 0 3 5 e r g s / s e c . The upper h a l f of t h i s range i s t y p i c a l of the l u m i n o s i t i e s of the strong X—ray bi n a r y c l a s s of g a l a c t i c , v a r i a b l e r a d i o source. At l e a s t one of the survey v a r i a b l e s (GT0236+610) e x h i b i t s many of the c h a r a c t e r i s t i c s of t h i s c l a s s of r a d i o source, which 209 i n c l u d e s such e x o t i c o b j e c t s as Cyg X—3, C i r X—1, Sco X—1 and SS 433. A n a l y s i s of the complete survey o b s e r v a t i o n s w i l l r e s u l t in a catalogue of about 2000 compact sources, and should r e v e a l a number of a d d i t i o n a l v a r i a b l e sources. These r e s u l t s w i l l provide a l a r g e l y unbiased specimen base f o r more d e t a i l e d s t u d i e s of h i g h l y v a r i a b l e r a d i o sources, and the u n d e r l y i n g p h y s i c a l mechanism(s). In view of the s i m i l a r i t y between some of the "known g a l a c t i c v a r i a b l e s (eg. Sco X—1 and SS 433) and compact e x t r a g a l a c t i c sources, the sample of short—term, g a l a c t i c v a r i a b l e s i s of p a r t i c u l a r i n t e r e s t . 210 BIBLIOGRAPHY Abies, J.G. 1969, Ap. J. Letters, 155, L27. Altenhoff, W.J., Braes, L.L., Olnon, F.M., Wendker, H.J., 1976, Astron. and Astrophys., 46, 11. , ' Altenhoff, W.J., Downes, D., Pauls, T. and Schraml, J. 1978, Astron. and Astrophys. Supp., 35_, 23. 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G R E G O R Y Department of Physics, University of British Columbia Received 1981 July 2i: accepted 1981 'October 6 ABSTRACT We report the discovery of periodic radio emission from the highly variable radio star LS I + 61°303. Based on an analysis of 144 flux density measurements, from 1977 August to 1981 March, we derive a period of 26.52 ± 0.04 days. Comparison of the radio light curves at 5.0 and 10.5 GHz rules out occultation as explaining the periodic variation. The implications of the radio emission are discussed in the context of a binary model, which also accounts for the X-ray and possible y-ray emission associated with the source. Subject headings: stars: individual — stars: radio radiation — X-rays: binaries I. I N T R O D U C T I O N Over the past 3 years, the star LS I + 61°303 has been the object of considerable observational effort because of its very unusual properties. In 1977 the highly variable radio source GT 0236+610 was discovered during a survey of the galactic plane for variable radio emission (Gregory and Taylor 1978) and suggested as the radio counterpart of the COS B gamma-ray source CG 135+01. Based on an accurate radio position, GT 0236 + 610 was identified with LS I +61°303 (Gregory et al. 1979), a B0 star at a distance of 2.3 kpc with unusually broad, double-peaked, and variable Ha and H/J emission lines. Originally thought to be a supergiant (Gregory et al), the star has been classified recently as a main-sequence B0-B0.5 (L = 10 3 8 ergss" \ Te„ = 2.6 x 104 K) emission-line star with a high rotational velocity, under-going mass loss through an equatorial disk (Hutchings and Crampton 1981). An HEAO 1 X-ray source at the position of the star was reported by Share et al. (1978). Bignami et al. (1980) have confirmed the identification of the X-ray emission with LS I + 61°303 using the IPC and HRI detectors of the Einstein Observatory. Low-energy gamma-ray emission from the direction of the star (posi-tional uncertainty ~ If 5 x 6°) was observed by Perottiet al. (1980). The radio emission from LS I + 61°303 is characterized by nonthermal outbursts with rise times of a few days and a typical duration of about 10 days. We have previously reported, in an IAU Circular, the detection of a 26.5 day period in the radio emission (Taylor and Gregory 1980). It is noteworthy that, with the exception of pulsars, LS I + 61°303 is one of only two known periodic radio sources (Circinus X-l, P = 16?59), and the first to be discovered solely through radio measurements. In this paper, we present the evidence for the periodicity, based on an analysis of all available flux density measurements of the source from 1977 August to 1981 March. I I . T H E D A T A Radio flux densities of LS I + 61°303 have been obtained primarily with two telescopes, at frequencies of 5.0 and 10.5 GHz. The majority of the 5.0 GHz flux densities are obtained from daily observations that have been carried out since 1977, for approximately 3 weeks in August of each year, as part of our survey for variable radio sources with the National Radio Astronomy Observatory (NRAO) 91 m transit telescope. A detailed description of the instrumentation and observing technique is given elsewhere (Gregory and Taylor 1981). An additional six flux densities have been obtained with the NRAO Very Large Array. All observations at 10.5 GHz have been made with the 46 m telescope of the Algonquin Radio Observatory (ARO) using the wagging technique described by Gregory et al. (1979). The resulting data set consists of 72 flux densities at 5.0 GHz and 72 at 10.5 GHz, spanning the time interval of 1314 days from 1977 August 12 to 1981 March 16. The complete data set, including the date and frequency of each observation, is listed in Table 1. Approximately two-thirds of the data are derived from seven observing sessions, four at 5.0 GHz and three at 10.5 GHz, during which the source was observed systematically for a number of consecutive days. Observing sessions at 5.0 GHz have a sample interval of 1 day. At 10.5 GHz, the sample interval varies from about 10 minutes to many hours, but, for the purposes of this analysis, high time resolution observations have been averaged over a mini-mum of about 0.5 days. Of the remaining data, about half T A B L E l LS I +61°303 R A D I O F L U X DENSITIES Julian Date Frequency Flux Density U T D a t e (2,440,000 + ) (GHz) (mJy) 1977 Aug 12 3367.98 5.0 53 ± 7 1977 Aug 14 3369.97 5.0 36 ± 6 1977 Aug 15 3370.97 • 5.0 36 ± 6 1977 Aug 16 3371.97 5.0 23 ± 5 1977 Aug 18 3373.96 5.0 44 ± 7 1977 Aug 23 3378.95 5.0 16 ± 5 1977 Aug 24 3379.95 5.0 74 ± 8 1977 Aug 25 3380.94 5.0 72 ± 8 1977 Aug 26 3381.94 5.0 243 ± 19 1977 Aug 27 3382.94 5.0 284 ± 2 1 1977 Aug 29 3384.93 5.0 195 ± 16 (Continued) 215 T A B L E 1—continued U T Date Julian Date (2,440,000+) Frequency (GHz) Flux Density (mJy) U T Date Julian Date (2,440,000+) Frequency (GHz) Flux Density (mJy) 1977 Aug 30. . 1978 Feb 12 .. 1978 Feb 13 .. 1978 Feb 18 .. 1978 Feb 19 .. 1978 Feb 20 .. 1978 Feb 21 .. 1978 Feb 22 .. 1978 Feb 23 .. 1978 Feb 24 . . 1978 Feb 25 .. 1978 Feb 26 . . 1978 Feb 27 .. 1978 Feb 28 .. 1978 M a r l . . . 1978 Mar 28 . 1978 Apr 1 . . . 1978 Apr 22 .. 1978 Jun30 .. 1978 Jul 15 . . . 1978 Aug9 . . . 1978 Aug 10.. 1978 Aug 11 .. 1978 Aug 13.. 1978 Aug 14.. 1978 Aug 15.. 1978 Aug 16.. 1978 Aug 17.. 1978 Aug 17.. 1978 Aug 18.. 1978 Aug 19.. 1978 Aug 20. . 1978 Aug 21 . . 1978 Aug 21 . . 1978 Aug 22. . 1978 Aug 22. . 1978 Aug 23. . 1978 Aug 24. . 1978 A u g 2 8 . . 1978 Aug 29.. 1978 Aug 30.. 1978 Sep 1.... 1978 Sep2 . . . . 1978 Dec 28 .. 1978 Dec 29 .. 1978 Dec 30. . 1978 Dec 31 .. 1979 Mar 29 . 1979 Mar 31 . 1979 May 30 . 1979 Jun 1.... 1979 Jul 23 .. . 1979 Aug 1 .. . 1979 Aug 2 . . . 1979 Aug 3 ... 1979 Aug 4 . . . 1979 Aug 5 . . . 1979 Aug 6 . . . 1979 Aug 8 .. . 1979 Aug 9 . . . 1979 Aug 10.. 1979 Aug 11.. 1979 Aug 12.. 1979 Aug 13.. 1979 Aug 14.. 1979 Aug 15. 1979 Aug 16.. 3385.93 3552.00 3553.00 3558.33 3559.50 3560.53 3561.29 3561.92 3562.96 3564.00 3564.92 3565.92 3567.08 3567.96 3568.92 3596.00 3599.00 3622.13 3690.38 3705.00 3729.99 3730.98 3731.98 3733.98 3734.97 3735.93 3736.97 3737.93 3737.97 3738.93 3739.96 3740.13 3741.17 3741.95 3742.13 3742.95 3743.17 3744.95 3748.93 3749.93 3750.93 3752.92 3753.92 3870.70 3871.75 3872.72 3873.72 3962.42 3963.55 4023.82 4025.61 4077.81 4086.56 4088.01 4089.00 4090.00 4091.00 4092.00 4093.99 4094.99 4095.98 4096.98 4097.98 4098.98 4099.97 4100.97 4101.97 5.0 5.0 5.0 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 5.0 5.0 10.5 10.5 5.0 5.0 5.0 5.0 5.0 5.0 10.5 5.0 10.5 5.0 10.5 5.0 10.5 10.5 5.0 10.5 5.0 10.5 5.0 5.0 5.0 5.0 5.0 5.0 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 169 + 14 60 ± 10 45 ± 5 0 ± 13 10 ± 13 7 + 13 0 + 1 3 0 ± 7 6 ± 7 19 ± 8 23 ± 6 3 0 + 8 68+ 7 82 ± 8 138 ± 8 160 + 20 150 ± 20 220 ± 8 15 ± 10 97 ± 5 176 ± 15 119+ 11 9 1 + 9 4 0 ± 6 27 ± 6 3 ± 13 1 5 + 5 0 ± 13 15 ± 5 0 ± 13 6 ± 4 15 ± 7 1 2 + 8 9 + 5 1 3 + 8 11 + 10 ± 12 ± 12 + 11 + 10 ± 8 ± 29 + 55 ± 13 86 ± 13 82 + 13 41 ± 13 51 ± 13 149 + 13 63 ± 13 55 ± 13 84+ 13 22 + 13 9 ± 5 12 ± 15 ± 13 + 12 ± 6 + 18 ± 48 ± 60+ 8 6 1 + 8 70 ± 8 83 ± 9 100 ± 10 68 ± 8 1979 A u g 2 0 . . 1979 Aug 21 .. 1979 A u g 2 6 . . 1979 Nov 21 . 1979 Nov 30 . 1979 Dec 7 . . . 1980 Jun 13 .. 1980 Jun 14 .. 1980 Jun 18 .. 1980 Jun 20 .. 1980 Jun 21 .. 1980 Jun 22 .. 1980 Jun 24 .. 1980 Jun 25 .. 1980 Jun 30 .. 1980 Jul 29 . . . 1980 Aug 19.. 1980 Aug 20. . 1980 Aug 21 . . 1980 Aug 22. . 1980 Aug 23 .. 1980 Aug 24 .. 1980 Aug 25. . 1980 Aug 27. . 1980 Aug 28. . 1980 A u g 2 9 . . 1980 Aug 30.. 1980 Sep 1.... 1980 Sep2 . . . . 1980 Sep 3 . . . . 1980 Sep4 . . . . 1980 Sep 5 . . . . 1980 Sep 6. . . . 1980 Sep7 . . . . 1980 Sep 8.. . . 1980 Sep 9 . . . . 1980 Sep 10 .. 1980 Sep 11 .. 1980 Sep 15 .. 1980 Sep 17 .. 1980 Sep 28 .. 1980 Oct 16 .. 1980 Oct 18 .. 1980 Oct 23 .. 1980 Oct 27 .. 1980 Oct 31 .. 1980 Nov 1... 1980 Nov 3 .. 1980 Nov 14 1980 Nov 17 1980 Dec 5 .. 1980 Dec 17 . 1980 Dec 18 . 1980 Dec 22 . 1980 Dec 23 . 1981 Jan 2 . . . 1981 Jan 5 . . . 1981 Jan 12 . 1981 Jan 17 . 1981 Jan 18 . 1981 Jan 19 . 1981 Jan 22 . 1981 Jan 22 . 1981 Jan 29 . 1981 Mar 7 . . 1981 Mar 16 4105.96 4106.95 4112.02 4198.57 4208.03 4214.90 4404.25 4405.28 4409.81 4411.78 4412.91 4413.88 4415.16 4416.54 4421.08 4449.82 4470.96 4471.96 4472.95 4473.95 4474.95 4475.95 4476.94 4478.94 4479.93 4480.93 4481.92 4483.92 4484.92 4485.92 4486.92 4487.91 4488.91 4489.91 4490.90 4491.90 4492.90 4493.90 4497.86 4499.97 4510.94 4528.96 4530.95 4535.99 4540.02 4544.02 4545.06 4547.06 4557.96 4560.96 4578.76 4580.76 4581.69 4585.78 4586.79 4606.66 4609.63 4616.75 4621.75 4622.74 4623.72 4626.73 4727.42 4633.64 4672.67 4682.47 5.0 5.0 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 10.5 5.0 10.5 10.5 10.5 4 5 + 7 91 ± 9 6 ± 13 35 ± 13 58 ± 13 17 + 13 26+ 13 19+ 13 1 4 + 9 17 + 24-22 ± 27 + 38 ± 20 ± 13 17 + 13 54 ± 7 27 ± 58 ± 23 • 30 ± 32 ± 27 + 25 ± 66 + 38 + 24 ± 17 ± 18 ± 12 + 10 ± 12 ± 5 ± 7 ± 10 ± 18 + 18 + 35 + 112 -48 + 9 ± 45 ± 36 ± 19 ± 9 ± 63 ± 9 4 + 8 57 + 13 24+ 17 0 ± 9 131 ± 9 80 ± 8 81 + 12 1 0 + 9 12 + 12 47 + 10 1 7 + 9 1 3 + 9 72 ± 8 146+ 8 146+ 8 78 ± 8 1 4 4 + 4 36 ± 8 22 ± 22 76 ± 9 6 7 5 6 6 6 6 8 6 5 5 5 5 5 5 4 4 5 5 5 6 10 9 8 9 9 9 9 9 212 come from a 10.5 Ghz monitoring program at ARO which began in 1980 October and has a sample interval ranging from 1 to 20 days. The rest of the data set consists of single observations carried out sporadically over the past 3 years. III. A N A L Y S I S A search of the radio data for periodicity was mo-tivated by the observation that, during six of the seven observing sessions, the source exhibited a similar radio light curve. The characteristic amplitude of the outburst is quite variable from session to session. However, the temporal evolution of the radio emission was observed to be relatively constant; a low state prior to or followed by an outburst with a duration of about 10 days. These observations provided a tentative indication of periodi-city on a time scale of about a month. The period search was carried out using a simple type of folding time analysis. Each flux density was assigned a phase based on an adopted trial period and binned into one of ten phase bins. The variation of the flux density in each bin is a measure of the scatter of the data about the mean "light curve." True periodicity will result in a minimum in the scatter at constant phase as the trial period approaches the true period. The intervals of continuous time coverage place a lower limit on the possible period of 24 days. The analysis was carried out for trial periods ranging from this lower limit to 100 days. The data at 5.0 and 10.5 GHz were analyzed indepen-dently to accommodate any systematic differences be-tween the light curves at the two frequencies. A 4 a minimum at 10.5 GHz and a 5 tr minimum at 5.0 GHz occur in the rms scatter of the flux densities averaged over all phase bins at a trial period of about 26.5 days. With the exception of the higher harmonics of 26.5, no other significant minima appear in the results. While this result provides strong evidence for periodi-city, this simple method of analysis is sensitive to the intrinsic variability in the magnitude of the outbursts, and the resulting noise reduces the accuracy to which the period can be determined. To refine our estimate of the period, we carried out a further analysis aimed at empha-sizing the repeatability of the shape, rather than the amplitude of the radio light curve. A mean radio light curve at each frequency was calculated, as in the previous analysis, by binning and averaging all of the data. This mean light curve was cross-correlated, in phase space, with the results from the six observing sessions which provide semicomplete coverage of a single outburst. The phase of the peak in the cross-correlated curve is a measure of the phase difference between the individual and mean radio light curves. For true periodicity, this phase difference is zero and constant. The rms variation in the phase of the cross-correlated peak for the six outbursts is shown in Figure 1. A 6.9 a minimum occurs at a trial period of 26.52 ± 0.04 days, which we take to be the best estimate of the radio period. The six outbursts are shown stacked and plotted in phase for this period in Figure 2. Phase zero has been arbitrarily set at Julian Date 2,443,366.775. I. 255 TRIAL PERIOD (DAYS) F I G . 1.—The rms phase scatter in the peak of the cross-correlation of the mean radio light curves with the individual outbursts. — 100 . 50 30 20 10 , 1 , , . , 1 . , 1 1 1 1 Aug. 1977 • 5 GHz -• • Feb. 1978 10 GHz Aug. 1978 -5 GHz • . .. • . . . . • • . - Aug. 1979 • . 5 GHz _ • • • • • • June 1980 • 10 GHz " *• Aug. 1980 5 GHz • 1 , , ,• • • ' "i I i i i i I i F I G . 2.—Radio outbursts covering a 3 year time interval plotted in phase for a period of 26.52 days. Julian Date of phase zero = 2,443,366.775. 216 TAYLOR AND GREGORY V 217 No. 1, 1982 RADIO EMISSION FROM LS I +61°303 213 IV. A L G O N Q U I N RADIO OBSERVATORY MONITORING P R O G R A M In 1980 October, we initiated a program at ARO to monitor systematically the 10.5 GHz flux density of LS I + 61°303 over a number of consecutive 26.5 day cycles in order to confirm the periodicity. The time interval be-tween observations is quite variable; however, during the five cycles from 1980 September to 1981 January, an observation was obtained on the average of once a week. In this time period, five distinct outbursts from the source were observed. Within the limited time resolution of the observations, the outbursts appeared regularly spaced, with a separation between outbursts consistent with a 26.5 day period. The complete results of the monitoring program to 1981 March are shown plotted in phase in Figure 3. Although the high variability of the source during its active phase is clearly evident, a definite cyclical radio light curve results. The light curve is particularly well defined from phase of turn-off at about 0.8 through its quiescent period extending to about phase 0.3. On the basis of these results, we confirm the periodicity of the radio emission from LS I +61°303. V. DISCUSSION Mean radio light curves at 5.0 and 10.5 GHz, and the two-frequency spectral index a, (S, oc v"), are shown in Figure 4. Due to the statistical nature of the flux densities and the known variability of the source, the detailed structure of the curves cannot be interpreted reliably. However, a flat spectrum measured at phase 0.6 during 1978 February (Gregory et al. 1979) agrees well with the mean results, and, in lieu of actual simultaneous two-frequency observations, it is useful to point out possibly significant trends in the available data. There is an indication of an earlier turn on at 10.5 GHz, and the associated spectral index is suggestive of absorption effects. Following this, at about phase 0.5, the source appears to become optically thin, and thereafter the spectral index is consistent with nonthermal synchrotron 150 ~ ii 1 1 M " I " 1 1 T i • • H 100 i i • • DENS i i i i i i,,T7 " " ' 1 iii i . : 1 | f i 1 ' 11 X 3 50 LL 1, i ' i - i i -i i, • 1 'M 7 1 1 1 l l 1 r > i i i i 1 r 1 0.2 0.4 0.6 0.8 0.0 0.2 0.4 0.6 0.8 F I G . 4.—Mean radio light curves at 5 G H z (solid (ine)and 10.5 G H z (dashed line). Also shown (bottom) is the two-frequency spectral index derived from the mean curves. F I G . 3 . — A R O 10.5 G H z flux densities from 1980 September to 1981 March plotted in phase. emission. The peak flux density of about 120 mJy yields a mean outburst luminosity of ~ 1032 ergs s"1. We interpret the periodicity of the radio emission as evidence of a binary system. Recently, Hutchings and Crampton (1981) have analyzed three years of radial velocity data to search for this period and find evidence for a period of 26.4 + 0.1 days, within error of the radio result. For a primary mass in the range from 5 to 10 Af ©, their orbital solutions yield a 1.1-1.5 M© secondary. A Keplerian orbit for this mass range and a 26.52 day period has a semimajor axis of0.32-0.39 AU, about 7-8 times the radius of the primary for R„ ~ 10 RQ. Before considering further the implication of the radio emission, it is worthwhile to review our present knowl-edge of LS I +61°303. Optical spectra obtained in 1978 by Hutchings and Crampton (Gregory et al. 1979) sug-gested that the star is a BI lb supergiant, although the weakness of the O n, Si m, and other lines, as well as the distance of 2.3 kpc based on association with IC 1805 indicated a lower luminosity. Observations made using the International Ultraviolet Explorer (WE) in the 1200-1950 A range (Hutchings 1979) showed a line spectrum of early-type B and P Cygni profiles indicating mass loss, which supported the case for a supergiant. However, the spectrum was peculiar in many respects, and, again, for the adopted distance, the luminosity was low for a supergiant. The results of further UV (1900-3200 A) and 218 TAYLOR AND GREGORY Vol. 255 214 optical spectroscopy were reported by Hutchings and Crampton (1981). The best model atmosphere fits to the UV continuum consistent with an early B spectral type yielded an effective temperature of 2.6 x 104 K and a bolometric luminosity of ~ 1 x 10 3 8 ergs s"1, values typical of a B0-B0.5 main-sequence star. Furthermore, the high signal-to-noise ratio optical spectra showed strong shell absorption lines and a high rotational velo-city, confirming that LS I +61°303 is a main-sequence object. Additional WE observations were carried out by Maraschi, Tanzi, and Treves (1981). The 2700-3100 A continuum flux was observed to vary by ~ 25 % over a period of 2 days. Their model-atmosphere fits to both the UV continuum and the t/BKcolors of Drilling (1975)and Roessiger (1978) yield, for a main-sequence star, a Teff of 1.5 x 104 K, indicating a spectral type near B5. This result is significantly different from that obtained by Hutchings and Crampton (1981) based on fits to the UV continuum alone. The difficulty in fitting the combined U V and optical continuum with a spectral type consistent with the line spectra, and the variability of the UV continuum, lead us to suggest the possibility that the spectrum is composite; a portion of the flux perhaps arising from a hot accretion disk around the companion. Hutchings and Crampton (1981) pointed out that, in a restricted latitude range (50°-80°), mass loss from Be stars may be similar to supergiant stellar winds, produc-ing the observed UV P Cygni lines. The majority of the circumstellar matter, however, resides in the equatorial plane, giving rise to the shell absorption lines. The presence of both P Cygni profiles and strong shell absorption lines in the spectra of LS I + 61°303 suggests that the star is viewed at an angle of 10°-20° from the equatorial plane. For a distance of 2.3 kpc, the X-ray flux of Share et al. (1978) and that of Bignami et al. (1980) correspond to a luminosity of ~ 1033 ergs s - 1. From an analysis of the COS B data, Pollock et al. (1981) conclude that LS I + 6T303 is the most probable counterpart of the gamma-ray source CG 135 + 01. The COS Bflux corresponds to a luminosity L (> 100 MeV) ~ 1035 ergs s~l, and the low-energy gamma-ray detection of Perotti et al. (1981) yields L (0.1-1 MeV) « 10 3 7 ergs s"l. The energy required to produce these high luminosities suggests that the com-panion is a degenerate star which, for a mass of ~ 1 M Q , could be either a white dwarf or a neutron star. Due to the rapid rotation of the primary, matter from the equatorial flow accreting onto the compact companion is likely to form an accretion disk. In this case, in the presence of a magnetic field (implied by the radio synchrotron emis-sion) relativistic electrons may be produced in a mag-netized accretion disk via a process similar to that described by Shields and Wheeler (1976). Alternately, Maraschi and Treves (1981) have proposed a model for LS I +61°303, in which the companion is a moderately young pulsar losing energy through a relativistic wind at a rate of 103 7 ergs s ~1. The relativistic wind is randomized in a shock region at the interaction boundary of the pulsar and stellar winds. From a consideration of pulsar models, they derive a magnetic field of 6 gauss in the boundary region, giving rise to synchrotron radiation from the relativistic electrons. The energy dissipated by the neutron star in this model precludes the formation of an accretion disk. However, in either case (accretion disk or young pulsar), the observed X-ray and gamma-ray emission can be accounted for by Cpmpton scattering of stellar photons by the relativistic electrons. We now consider what information can be obtained about the physical conditions of the source from its radio properties, with a view to placing further constraints on possible models of the system. Models of the stellar wind type of Be star envelopes are well reviewed by Marlborough (1976) and Poeckert (1981). Typical mass loss rates are ~ 10~8 M© yr" 1 with expansion velocities in the equatorial plane, at a distance of a few stellar radii, of about 50 km s"i. The uniform radial mass flow model of Wright and Barlow (1975), restricted to a solid angle Q, yields a gas number density n = A/r2, where A M If we approximate the geometry of the equatorial mass loss by a symmetric radial flow with an angular extent <j> perpendicular to the equatorial plane, then Q = 2n (1-cos 4>). Taking 0 = 40°, M=10~ 8 M Q yr" 1, = 50 km s _ 1, and n = 1.26, the number density of electrons for a fully ionized plasma is n = 4 x 1034r""2. For a gas temperature of about 104 K, the optical depth in the equatorial plane along a radial line of sight to radius r at 10.5 GHz is given by t(r)=7.5 x 10" 2 8 j"°°«2dr. An optical depth of 1 corresponds to r ~ 5 AU. Since the vertical extent of the equatorial disk at radii comparable to the separation of the binary components is only a fraction of an AU, synchrotron emission from an expand-ing cloud of relativistic electrons originating at, or inter-ior to, the secondary would come mainly from the polar regions of the system. As the electrons emerge from the high-density equatorial region, radiation would be seen first at higher frequencies, consistent with the earlier turn on at 10.5 GHz suggested by the radio light curves. Some information about the radio emission region can be inferred from the observed decay time of about 6 days for the 10.5 GHz radiation. From synchrotron theory, electrons radiating at 10.5 GHz have an energy E = 4.1 x 10~ 5B~1,2 ergs and a lifetime due to synchro-tron losses of ts = 10 7B" 3 / 2 s. If the decay is attributed to synchrotron radiation losses, a magnetic field of ~ 7 gauss is required. For comparison, the radio luminosity of 10 3 2 ergs s~1 and the 3 AU upper limit on the size of the emission region (Gregory et al. 1979) yields an equiparti-tion magnetic field strength Btq > 2 gauss. For a field of a few gauss, the luminosity of 10 3 2 ergs s _ 1 requires a total energy in relativistic electrons of ~ 10 3 8 ergs. 219 No. 1, 1982 The mean radio curves also clearly show a more rapid decay of the radiation at higher frequency. Since the frequency dependence of the opacity of a thermal plasma is Kv oc v - 2, this observation rules out interpretation of the periodic radio variation in terms of an occultation of a continuous radio source, which would produce the oppo-site effect. The radio curves, therefore, support the sug-gestion that the periodic emission is due to the periodic production and subsequent energy decay of relativistic electrons. High time resolution radio observations at 10.5 GHz during the rising portion of the 1978 February outburst (Gregory et al. 1979) show that the particle production is episodic, on a time scale of about a day and continuing for about 8 days, up to the time of maximum flux density. If the acceleration mechanism is coupled to an accretion process, the phase of particle production may coincide with periastron passage of an eccentric orbit. Requiring a minimum orbital separation, rmin = _ greater than the radii of the primary places an upper limit on e of ~ 0.9. If we assume that the ~ 10 3 8 ergs in relativistic elec-trons required to explain the radio emission also powers the gamma-ray emission by Compton scattering the stellar photons, a maximum radius can be established for the location of particle production. For a primary with an effective temperature of ~ 2 x 104 K, the peak in the photon energy distribution occurs at about 10 eV. The generation of 1-100 MeV gamma-rays from these pho-tons by Compton scattering requires electron energies of 10~4-10~3 ergs. Gamma-ray luminosities as high as 10 3 7 ergs s~1 imply Compton lifetimes (fc) for these electrons of the order of tens of seconds, or photon energy densities of the order of 103 ergs cm "3. For a primary luminosity of 1038 ergs s~photon energy densities of this magnitude occur only near the surface of the star. The energetic electrons must therefore be created within ~ 1012 cm of the stellar surface, the distance traveled at v = c in a few tens of seconds. We note that an orbit with r m i n = 10 1 2 cm has an eccentricity of ~ 0.8. Since the gas density in the equatorial plane at r = 1012 cm is only about 4 x 10 1 0 cm - 3 the material is transparent to both 10 eV photons and hard X-rays and gamma-rays. However, because of the short lifetimes of the scattering electrons, the gamma-ray emission region may be small enough that the effects of occultation by the primary become important. As a further consequence of the short electron lifetimes, gamma-rays should appear only during periods of par-ticle production. Compton scattering of stellar photons into soft X-rays (~ 1 keV) requires electron energies of ~ 10"6 ergs, which at r= 1012 cm have a lifetime tc~ 10s s. The resulting luminosity of ~ 1033 ergs s~1 agrees well with the observations. If an accretion disk is present, a portion of this flux may arise from thermal X-rays produced in the hot inner regions of the disk. In this case, LS I +6T303 should be a continuous soft X-ray source. The total column density along a radial line of sight in the equator-ial plane to r = 1012 cm is 4 x 1022 cm - 2. This value is similar to the interstellar column density to LS I + 61°303 but, since the circumstellar material is highly ionized, 215 photoelectric absorption in the equatorial disk will be negligible compared to the interstellar effect. If the relativistic electrons are produced at r ~ 1012 cm, the short Compton lifetimes in this region must be reconciled with the postoutburst decay time of 6 days at radio wavelengths. For a field of a few gauss, electrons radiating at 10.5 GHz have an energy of about 10"5 ergs. Setting tc = 6 days leads to a lower limit on the outer radius of the synchrotron emitting region of 1013 cm, about twice the.semimajor axis of the orbit. The synchro-tron emitting electrons must therefore have propagated outward. If these electrons travel outward with velocity vr and have initial energy E0 at radius r 0, then at radius r the energy remaining after Compton losses is given by where tc(r0) is the Compton lifetime at radius r0. For r > r0, the electrons will retain a significant fraction of their energy if For r 0 = 10 1 2 cm and an initial energy £ 0 = 10"5 ergs, tc(r0) = 104 s. The synchrotron radiating electrons must therefore have a drift velocity with a radial component vrZ 108 cm s"1. The interpretations and arguments presented here combine to form a somewhat general scenario for LS I + 61°303, with little attention given to the details of the processes involved, particularly regarding the particle acceleration mechanism. The young pulsar model of Maraschi and Treves (1981) readily provides the highly energetic electrons required to produce the observed gamma-rays via Compton scattering. However, the par-ticle production in this case is continuous, which, since occultation is ruled out by the radio spectrum, is difficult to reconcile with the periodic radio variation. If, however, the particle acceleration is linked to an accretion process, the periodic variation may arise from a periodic trigger-ing of particle production due to an increase in the accretion rate at periastron passage of a highly eccentric orbit. It would be worthwhile to search for evidence of an accretion disk. One method might be to look for a softening of the X-ray spectrum outside of the phase of particle acceleration (</> ~ 0.8-0.3). Gamma-rays, on the other hand, should appear only in the phase range from 0.3 to 0.8. An analysis of the COS B data to test this prediction would be valuable. If, as indicated, the radio emission arises mainly from the polar regions of the system, the radio source should be elongated in the polar direction with a dimension > 1013 cm. At 2.3 kpc, this corresponds to an angular extent > 0.3 milli-arcsec, which should be resolvable by intercontinental VLBI. We would like to thank Dr. John M. MacLeod and the staff of ARO, in particular Walter M. Turner, for their assistance in carrying out the 10.5 GHz monitoring RADIO EMISSION FROM LS I +61°303 220 216 TAYLOR A observations. We would also like to acknowledge useful discussion with Dr. John Hutchings. The ARO is part of the Herzberg Institute of Astrophysics operated by the National Research Council of Canada. The NRAO is GREGORY operated by Associated Universities, Inc., under contract with the National Science Foundation. This research was supported by a grant from the Natural Science and Engineering Research Council of Canada. R E F E R E N C E S Bignami, G . F„ Caraveo, P. A., Lamb, R. C , and Markert, T. H . 1980, IAU Circ, No. 3518. Drilling, J. S. 1975, Ap. J., 80, 129. Gregory, P. C , and Taylor, A . R. 1978, Nature, 272, 704. Gregory, P. C , and Taylor, A . R. 1981, Ap. J., 248, 596. Gregory, P. C , et at. 1979, AJ., 84, 1030. Hutchings, J. B. 1979, Pub. A.S.P., 91, 657. Hutchings, J. B., and Crampton, D. 1981, Pub. A.S.P., 93, 486. Maraschi, L., Tanzi, E. G., and Treves. A. 1981, Ap. J., 248, 1010. Maraschi, L., and Treves, A. 1981, M.N.R.A.S., 194, IP. Marlborough, J. M . 1976, in IAU Symposium 70, Be and Shell Stars, ed. A. Slettebak (Dordrecht: Reidelj, p. 335. Perotti, F., Delia Ventura, A., Villa, G., Di Cocco, G., Butler, R. C , Dean, A. J , and Hayles, R. I. 1980, Ap. J. (Letters), 239, L49. Poeckert, R. 1981, in IAU Symposium 98, Be Stars, ed. M . Jaschek and H . G . Groth (Dordrecht: Reidel), in press. Pollock, A . M . T , Bignami, G . F., Hermsen, W„ Kanbach, G., Lichti, G . G., Masnou, J. L. , Swanenburg, B. N . , and Wills, R. D. 1981, Astr. Ap., 94, 116. Roessiger, S. 1978, IAU Circ, No. 3210. Share, G . H., et al. in X-Ray Astronomy, Proc. of the 21st Plenary Meeting of the Committee on Space Research, ed. W. A. Baity and L. E. Peterson (New York: Pergamon), p. 535. Shields, G . A., and Wheeler, J. C. 1976, Ap. Letters, 17, 69. Taylor, A. R., and Gregory, P. C. 1980, IAU Circ, No. 3464. Wright, A. E., and Barlow, M . J. 1975, M.N.R.A.S., 170, 41. A. R. TAYLOR and P. C. GREGORY: Department of Physics, University of British Columbia, Vancouver, British Columbia Canada, V6T 2A6 PUBLICATIONS: Gregory, P.C. and Taylor, A.R. "New Highly Variable Radio Source, Possible Counterpart of 2-ray Source CG135+1", Nature 272, 704-706, (1978) Feldman, P.A., Taylor, A.R., Gregory, P.C, Seaquist, E.R., Balonek, T.J., and Cohen, N.L. "Discovery of Strong Radio Flaring from HR1099", Astron. J. 83, 1471-1484 (1978). Seaquist, E.R., Garrison, R.F., Gregory, P.C, Taylor, A.R., and Crane, P.C. "Radio and Optical Observations of SS 433", Astron. J. 84, 1037-1041, (1979), Gregory, P.C, Taylor, A.R., Crampton, D., Hutchings, J.B., Hjellming, R.M., Hogg, D., Hvatum, H., Gottlieb, E.W., Feldman, P.A., and Kwok, S. " The Radio, Optical, X-ray(?), j-ray (?) Star LSI+61°303", Astron. J., 84, 1030-1036, (1979). Gregory, P.C. and Taylor, A.R. "Radio Patrol of the Northern Milky Way: A Survey for Variable Sources", Astrophys. J. 248, 596-605, (1981). Taylor, A.R. and Gregory, P.C "Periodic Radio Emission from LS I +61°303", Astrophys. J. 255, 210-216, (1982). 

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