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Observations of planetary nebulae with multi-element image sensors Condal, Alfonso Ramon 1979

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• 9 « OESEEVATIONS OF PL ANETAEY NEBULAE WITH MULTI-ELEMENT IMAGE SENSOES by ALFONSO BAMON CONDAL Diploma, U n i v e r s i t y of C h i l e , 1965 W.Sc«, U n i v e r s i t y of Alaska, 1971 THESIS SUBMITTED IN PAETIAL FULFILLMENT OF THE EEQUIEEMENTS FOE THE DEGBEE OF DOCTOE OF PHILOSOPHY in THE FACULTY OF GEADUATES STUDIES (Department of Geophysics and Astronomy) We accept t h i s t h e s i s as conforming t o the r e q u i r e d standard The U n i v e r s i t y of B r i t i s h Columbia September, 1979 0 A l f o n s o Eamcn Condal, 1979 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date >6 B P 75-5 1 1 E A b s t r a c t Two s i l i c o n diode arrays have been used to o b t a i n s p e c t r a of the p l a n e t a r y nebula NGC 7027,. . R e l a t i v e l i n e i n t e n s i t i e s (I(Hc()=100) are determined i n the s p e c t r a l r e g i o n 5000-9900A. The r e s o l u t i o n , good quantum e f f i c i e n c y , and the wide dynamic range a v a i l a b l e with these d e t e c t o r s permit: i ) the r e s o l u t i o n of c l o s e p a i r s f o r which only the blend i n t e n s i t y i s p r e s e n t l y a v a i l a b l e , e,.g. Paschen P8 9546 frcm the £S I I IJ 9532, and H e l l 6683 from Hel 6678. i i ) A much c l o s e r value o f the t h e o r e t i c a l r a t i o f o r the £ S I I I ] 9069, 9532 l i n e s t o be obtained. i i i ) A b e t t e r agreement with model p r e d i c t i o n s f o r the i n t e n s i t i e s of the [Nil]] doublet at 6548, 6584. T h i s p l a n e t a r y was a l s o observed with a 50x50 a r r a y through i n t e r f e r e n c e f i l t e r s centered at £0111J 5007 , H o ( 6563, and i SII i] 6731. Regions of low and high e x c i t a t i o n are determined by i n s p e c t i o n of the r a t i o s I S I I i J / H o c and £ SII ] / £ O I I I J . . V a r i a b l e e x t i n c t i o n a c r o s s the f e c e o f the nebula i s shown t o e x i s t by c o n s t r u c t i n g a two-dimensional map of the c o l o r excess E (Ho<-£ OI I I J) A JPL CCD camera was used t o o b t a i n iccnccromatic images of the p l a n e t a r y nebulae NGCJ 2440, NGC 3132, and NGC 3242 i i i through i n t e r f e r e n c e f i l t e r s centered a t Hp 4861, H* 6563, [ N i l ] 6584, and [ S I I I J 9532 . . Two-dimensional data i s presented i n the form of f a l s e - c o l o r photographs obtained with a Comtal Imaging System. , T h i s system has the c a p a b i l i t y of producing images with a b r i g h t n e s s r e s o l u t i o n of 8 b i t s per p i x e l i n shades of gray, f a l s e or f u l l c c l o r . Computer programmes have been w r i t t e n t o handle the t r a n s f e r of data frames from the main computer at UBC t o the Comtal Imaging System. . k two envelope s t r u c t u r e , s t r a t i f i c a t i o n of t h e . r a d i a t i o n and l o c a l d e n s i t y f l u c t u a t i o n s are obvious f e a t u r e s of the images of NGC 2440, NGC 3132, and NGC 3242. A l l of them are c o n s i s t e n t with an e j e c t i o n o f matter from a c e n t r a l s t a r with non-zerc angular momentum. Eegions of low and high e x c i t a t i o n are determined from the r a t i o s £NIIiJ/Ho(, . i SIII ft/H^, and [ S I I I J/[NII J . C o l o r excess maps show thf.t v a r i a b l e e x t i n c t i o n i s a l s o present i n these objects.„ Since the c o l o r excess i n c r e a s e s outward f o r a l l of these o b j e c t s , the i n d i c a t i o n i s t h a t the dust r e s p o n s i b l e f o r t h i s e x t i n c t i o n i s concentrated more i n the outer envelope than i n the i n n e r envelope. i v Table of Contents I. I n t r o d u c t i o n ........................................ 1 1.1 H i s t o r i c a l Background ............................. 1 1.2 Gaseous Nebulae ................................... 5 1.3 The O p t i c a l Spectra Of Emission Nebulae ............ 9 1.4 E x t i n c t i o n To Planetary Nebulae ......................15 1.5 The Programme ..................................... 24 IX. Observations And Data Reductions ...................31 2.1 S o l i d S t a t e Imaging Devices ....................... 31 2.2 S p e c t r o s c o p i c Observations .........................41 2.3 Data Reduction ....................................51 2.4 P r e c i s i o n Of The Measurements ..................... 60 2.5 Monochromatic Two-dimensional Observations ........ 80 2.6 Data Reductions ................................... 87 2.7 The Comtal V i s i o n One Imaging System .................. 9 3 I I I . . NGC 7027 ,..,,.98 3.1" Basic Data ............................................. .98 3.2 Emission S t r u c t u r e ..................................106 3.3 L i n e R a t i o s ...... .............111 3.3 Comparison Of S p e c t r o s c o p i c Observations With Theory 123 IV, .. NGC 2440, NGC 3132, And NGC 3242 ....................... 135 4.1 NGC 2440 ,..,.,...,..135 4.2 NGC 3132, ................ It ......................... . 148 4.3 NGC 3242 ......,.....,, 155 Summary And Con c l u s i o n s v i l i s t o f T a b l e s Table I The DBC Diode Array Systems ..................... 33 Table I I Performance Parameters For The Detector Systems . . , 40 Table I I I S p e c t r o s c o p i c Observations ................... 42 Table IV Nebulae Observed ............................... 43 Table V R e l a t i v e L i n e - r a t i o s ............................ 43 Table VI R e l a t i v e L i n e - r a t i o s : NGC 7027 .........55 T aisle V II E r r o r Estimates ............................... 64 Table VIII S c a l i n g F a c t o r s : C 67 Table IX T h e o r e t i c a l And Observed Line Ratios ...........19 Table X I n t e r f e r e n c e F i l t e r s .„,, .......................... 8 1 Table XI Gaseous Nebulae Observed ....................... 81 Table XII NGC 7027: Dimensions And I n t e n s i t i e s ..........109 Table X I I I NGC 7027: E x t i n c t i o n ' Values .....................116 Table XIV NGC 7027: l o b s Vs I t h e o . . . . . . . . . . . . . . . . ..129 Tab l e XV NGC 7027: Te And Ne Values ....................... 131 Table XVI NGC 2440: E x t i n c t i o n Values ...................,1.45 Table XVII NGC 3132: Dimensions And I n t e n s i t i e s ....15 2 Table XVIII NGC 3132: E x t i n c t i o n Values -.154 Table XIX NGC 3242: Dimensions And I n t e n s i t i e s ..........,160 Table XX NGC 3242: E x t i n c t i o n Values 16 2 v i i L i s t of F i g u r e s F i g u r e 1 L i n e a r Approximation To E x t i n c t i o n Curve ....... .21 F i g u r e 2 CCD Expected S p e c t r a l Response ................. 38 F i g u r e 3 1024 Reticon Vs K a l e r Et A l . (1976) ............ 63 F i g u r e 4 O b s e r v a t i o n a l E r r o r Vs Wavelength ............... 69 Fig u r e 5 Schmidt Camera Vs Kaler Et A l . . (1976) ......... 70 Fig u r e 6 Wynne Camera Vs K a l e r Et A1. . (1976) ........... 71 F i g u r e 7 Wynne Camera Vs Kaler Et A l . : (1976) ............ 72 Figure 8 Schmidt Camera:EAO Vs MKO, KPNO , 7 3 F i g u r e 9 NGC 7027: Paschen Decrement.................... 74 F i g u r e 10 NGC 7027 : H e l l Pfund Decrement 75 F i g u r e 11 NGC 3132: 9532A:No F.F. C a l i b r a t i o n ........... 91 F i g u r e 12 F u n c t i o n Maps ................................. 96 F i g u r e 13 Saturn: CTIO Jan 1 9 7 8 - i i , . . . . . . . . . . . . . . . . . . . . . . 97 Figure 14 NGC 7027: DAO Sept 1976 .......................... 10 8 F i g u r e 15 NGC 7027: [ O I I I ] Image 110 F i g u r e 16 NGC 7027: Line R a t i o s ,120 Fig u r e 17 NGC 7027: l o b s Vs Itheo ....................... 128 F i g u r e 18 NGC 2440: .............. 137 F i g u r e 19 NGC 2440:CTIO January 1978 140 Figure 20 NGC 2440:CTIO January 1S78 ................141 F i g u r e 21 NGC 2440: Schematic S t r u c t u r e ,.,...146 Fi g u r e 22 NGC 3132: CTIO January 1978 150 F i g u r e 23 NGC 3132: L i n e R a t i o s ......................... 151 F i g u r e 24 NGC 3242: CTIO January 1978 ................... 157 v i i i f i g u r e 25 NGC 3242: L i n e E a t i o s .......................... 159 F i g u r e 26 NGC 3242: Schematic S t r u c t u r e ................. 164 F i g u r e 27 U.B.C. Data System .........181 Acknowledgments I would l i k e t o express my a p p r e c i a t i o n to my s u p e r v i s o r , Er. G.A.H. Walker, f o r h i s continued. a i d , encouragement and o v e r a l l guidance without which t h i s t h e s i s would have teen i m p o s s i b l e . , The other members of my Adv i s o r y Committee read the t e x t i n d e t a i l , and o f f e r e d many sugg e s t i o n s f o r i t s improvement. My thanks also to : Drs. G. , Falhman and J . Glaspey f o r p r o v i d i n g the computer programs needed f o r the r e d u c t i o n of the s p e c t r o p h o t c m e t r i c data and many i n v a l u a b l e d i s c u s s i o n s ; Dr. C. P r i t c h e t helped i n the r e d u c t i o n of the CCD data and a s s i s t e d with the o b s e r v a t i o n s ; Dr. , S. Mochnacki shared seme tel e s c o p e time and a s s i s t e d with the o b s e r v a t i o n s ; Dr.. R. Woodham and Mr., S., Deering provided a s s i s t a n c e with the Comtal System; Mr. V. Buchholz provided i n v a l u a b l e help with the i n s t r u m e n t a t i o n . I am very g r a t e f u l t o the D i r e c t o r s and s t a f f o f the Dominion A s t r o p h y s i c a l Observatory and Cerr o T c l o l o I nteramerican Observatory f o r g r a t i n g observing time and a s s i s t i n g with the o b s e r v a t i o n s , , L a s t , but not l e a s t , I thank my wife N i k i f o r her X p a t i e n c e a s s i s t i n g me t o prepare the o r i g i n a l manuscript. .. 1 I. INTRODUCTION 1. 1 HISTORICAL BACKGROUND Nebulae have been known t o astronomers f o r a long time. The O r i o n Nebula was di s c o v e r e d i n 1610, and the b r i g h t e r p l a n e t a r i e s by William and John H e r s c h e l . Eut, u n t i l 30 years ago, the term nebulae was used r a t h e r l o c s e l y t o denote what we now c a l l g a l a c t i c (or d i f f u s e ) nebulae, p l a n e t a r y nebulae, g a l a x i e s , and s t a r c l u s t e r s . . Good examples cf t h i s s i t u a t i o n are The Messier (1787) and New General (1888) c a t a l o g u e s . . By 1864 Huggins had d i s c o v e r e d t h a t p l a n e t a r i e s and the Orion Nebula showed a b r i g h t l i n e emission s p e c t r a and t h e r e f o r e c o n s i s t e d of incandescent gas. The composition of t h i s gas was a matter of con t r o v e r s y f o r a long time and the i d e a t h a t the s t r o n g e s t l i n e s i n the s p e c t r a cf nebulae were due to a new element (nebulium) p r e v a i l e d u n t i l 1927 when Bowen i d e n t i f i e d these l i n e s as being produced by i o n i z e d oxygen, but under p h y s i c a l c o n d i t i o n s t o t a l l y d i f f e r e n t from 2 these i n l a b o r a t o r i e s . The f i r s t photographs of nebulae were obtained by C u r t i s at the beginning of t h i s century, while the f i r s t systematic o b s e r v a t i o n s of t h e i r s p e c t r a were made by Wright (1917).. S l i p h e r (1913) pointed out the d i f f e r e n c e between emission and r e f l e c t i o n nebula when observing the spectrum of the nebula a s s o c i a t e d with the P l e i a d e s C l u s t e r , and Hubble (1922) e s t a b l i s h e d t h a t emission nebulae were a s s o c i a t e d with s t a r s of s p e c t r a l type 0 to B1, while r e f l e c t i o n nebulae were a s s o c i a t e d with s t a r s of s p e c t r a l type l a t e r than B1. Subsequently, both the o b s e r v a t i o n a l and the t h e o r e t i c a l i n v e s t i g a t i o n of these o b j e c t s developed very r a p i d l y and the t h i r t i e s marked the beginning of our understanding o f the ph y s i c s of these o b j e c t s , a f t e r quantum mechanics made i t p o s s i b l e to i n t e r p r e t e t h e i r s p e c t r a q u a n t i t a t i v e l y . Zanstra and Bowen (1927) e x p l a i n e d the emission of l i g h t from nebulae by f l o u r e s c e n c e , Ambarzumian (1933) developed the theory of r a d i a t i v e e q u i l i b r i u m i n p l a n e t a r i e s , and Menzel (1935) i n i t i a t e d h i s long s e r i e s of papers i n the A s t r o p h y s i c a l J o u r n a l on P h y s i c a l Processes i n Gaseous Nebulae. The d i s c o v e r y by Struve of almost c i r c u l a r r e g i o n s 3 of f a i n t Hot emission l e d the way to the i n t r o d u c t i o n of the concept of HI and HII Regions by Stromgren i n 1939,. In the f o r t i e s , Minkowski d i s c o v e r e d s e v e r a l new p l a n e t a r i e s , s t u d i e d t h e i r space d i s t r i b u t i o n and d i s t a n c e s , and was one of the f i r s t to o b t a i n h i g h - r e s o l u t i o n monochromatic photographs of these o b j e c t s . In the mid-1S50's S h k l c v s k i i proposed t h a t p l a n e t a r i e s o r i g i n a t e d from red giant s t a r s of moderate mass. , Subsequent r e s e a r c h concentrated on o b t a i n i n g more accurate o b s e r v a t i o n s ( A l l e r , Osterbrock and co-wcrkers) and the c a l c u l a t i o n of r e a c t i o n r a t e s i'for the atomic processes i n v o l v e d i n the p h y s i c s of these o b j e c t s (Seaton and co-workers). Radio data became a v a i l a b l e i n 1960, d e t e c t i o n of molecular emission i n 1963, and i n f r a r e d o b s e r v a t i o n s i n 1S65. In t h e s e v e n t i e s , B r o c k l e h u r s t (1970, 1971) presented c a l c u l a t i o n s on the l e v e l p o p u l a t i o n s of hydrogen up to n=300 and i o n i z e d helium up to n=40 f o r a wide range of e l e c t r o n d e n s i t i e s and temperatures. , Flower (1969) c o n s t r u c t e d models cf p l a n e t a r y nebulae t h a t i n c l u d e d H, He, C, N, 0 and Ne i n t h e i r composition.. Kovach (1971) presented models of "dusty" p l a n e t a r y nebulae, c a l c u l a t i n g 1 the emission emitted i n the i n f r a r e d by the dust. F i n a l l y , j u s t i n the l a s t few y e a r s , 4 s a t e l l i t e o b s e r v a t i o n s have begun to provide i n f o r m a t i o n i n the u l t r a - v i o l e t p a r t o f the spectrum (Grewing et a L . 1978). 5 li.2 GftSEOUS NEBOL&E The e x i s t e n c e of an i n t e r s t e l l a r medium was demostrated by Hartmann i n 1 9 1 1 , but the r e l a t i o n s h i p between nebulae and clouds of gas and dust was not recognized immediately.. The present idea suggests t h a t nebulae are p a r t of the i n t e r s t e l l a r medium, clouds of gas and dust which are c l a s s i f i e d i n t o two l a r g e groups: dark and luminous.. The luminous are, i n t u r n , d i v i d e d i n t o r e f l e c t i o n and e m i s s i o n nebulae. R e f l e c t i o n nebulae are mainly c l o u d s of dust t h a t shine by s c a t t e r i n g l i g h t from s t a r s embedded i n them. The best example of t h i s type of nebula i s the one.arcund the P l e i a d e s . Emission nebulae are, i n t u r n , mainly c l o u d s of gas near hot s t a r s t h a t shine by a f l u o r e s c e n c e process which depends on i o n i z a t i o n of hydrogen and helium by r a d i a t i o n beyond the Lyman s e r i e s l i m i t . , T h i s type of nebula i s s u b d i v i d e d i n t o t h r e e d i f f e r e n t groups: i) H.II Regions; r e g i o n s of i o n i z e d gas, dust, and s t a r formation, found i n g a l a c t i c s p i r a l arms. 6 i i ) P l a n e t a r y nebulae; s h e l l s mainly of gas that i a v e been e x p e l l e d by a s t a r at some stage of i t s e v o l u t i o n . i i i ) Supernova remnants T h i s l a s t group o f emission nebulae, supernova remnants, d i f f e r s g r e a t l y from both HII Regions and p l a n e t a r i e s and, consequently, are u s u a l l y s t u d i e d s e p a r a t e l y . They are o b j e c t s where c o l l i s i o n a l i o n i z a t i o n plus non-thermal r a d i a t i o n , r a t h e r than p h o t o i o n i z a t i o n , are the e x c i t a t i o n mechanisms and show a r a t h e r f i l a m e n t a r y s t r u c t u r e . The best known of these o b j e c t s i s the Crab Nebula, remnant of the 1024 A,. D. supernova. Supernova remnants and r e f l e c t i o n nebulae w i l l not be considered i n t h i s t h e s i s , and t h e i r e x i s t a n c e i s j u s t mentioned f o r completeness. So f a r as atomic processes are concerned, HII Regions and pl a n e t a r y nebulae are q u i t e s i m i l a r , but the o r i g i n , ' mass, e v o l u t i o n and age of t y p i c a l members of these two groups are q u i t e d i f f e r e n t . T y p i c a l p h y s i c a l parameters f o r HII Regions a r e : (Osterbrock 1974) Age 5 x 106 yea rs Mass ( i o n i z e d p a r t of the nebula) 103M Density ( i o n i z e d p a r t of the nebula) 102 Cm -3 7 I n t e r n a l motions (turbulent) lOkmsec - 1 Logarithmic abundances by number a r e : H=12.00, He = 11.00, C=8.52, N=7. 76, 0=8.15, Ne=7.90, S=7. 41, Cl=5. 15, ftr=6.7 Throughout the nebula, hydrogen i s i o n i z e d , helium i s s i n g l y i o n i z e d , and the other elements are s i n g l y or doubly i o n i z e d . The e f f e c t i v e temperatures of the s t a r s a s s o c i a t e d with the n e b u l a are of the order of 3 to 5 x 10* K. T y p i c a l parameters f o r p l a n e t a r y nebulae are: (Osterbrock 1974) Age 1.2 x 10* years Mass 0. 2 to 1. OM Density 10*cm~ 3 Expansion v e l o c i t y ( p o s i t i v e outward) 25kmsec _ 1 l o g a r i t h m i c abundances ty number a r e : H=12.00, He=11.04, C=9.5, N=8.33, 0=6.87, Ne=8,28. The He/H, 0/H, and Ne/H abundance r a t i o s are s i m i l a r to those of the O r i o n N s l u l a while C/H and N/H abundance r a t i o s are l a r g e r by f a c t o r s of nine and f o u r r e s p e c t i v e l y . Only t h r e e g a l a c t i c p l a n e t a r y nebulae are known t o have abundances of 0 and Ne r e l a t i v e t o H tha t are d i f f e r e n t from those i n the Sun o r HII Begions (cne of them i n the g l o b u l a r c l u s t e r M15). 8 T y p i c a l e f f e c t i v e temperatures and absolute magnitudes f o r the c e n t r a l s t a r s are TCJ| ^  10s K and Mv -3 +5. As a r e s u l t , p l a n e t a r y nebulae show a higher degree of i o n i z a t i o n than HII Regions, u s u a l l y i n c l u d i n g He++ i n t h e i r c o m p o s i t i o n . C u r t i s (1918) n o t i c e d that p l a n e t a r y nebulae f e l l i n t o two g a l a c t i c l a t i t u d e groups.. L a t e r s t u d i e s by G r e i g (1971) and Cudworth (1974) showed that the C u r t i s * c l a s s i f i c a t i o n i c o r r e l a t e d with observed p h y s i c a l parameters and there were d e f i n i t e d i f f e r e n t morphological, k i n e m a t i c a l and p h y s i c a l p r o p e r t i e s between these two c l a s s e s of p l a n e t a r i e s . Greig c a l l e d these two c l a s s e s B and C., B type nebulae pres e n t s a f i l a m e n t a r y s t r u c t u r e and have s t r o n g f o r b i d d e n l i n e s of £ 0 1 1 ] , [ O i l ] , and £ N i l ] r e l a t i v e to H*. , C type nebulae presents a c e n t r a l i n c r e a s e i n b r i g h t n e s s and t h e i r f o r b i d d e n l i n e s are weak r e l a t i v e t o Ho(. 9 1.3 THE OPTICAL SPECTRA OJ EMISSION NEBOLAE The s p e c t r a of emission nebulae c o n s i s t of emission l i n e s superimposed on a f a i n t continuum. The continuum i s due to r a d i a t i v e recombination, f r e e - f r e e t r a n s i t i o n s and two-photon emission. Nebulae a l s o show a r e f l e c t i o n continuum due to s t a r l i g h t s c a t t e r e d by dust. The primary e x c i t a t i o n mechanism f o r the emission nebulae i s p h o t o i o n i z a t i o n of ground s t a t e atoms and i o n s by d i l u t e s t e l l a r u l t r a - v i o l e t r a d i a t i o n , , Obviously, the m a j o r i t y o f the f r e e e l e c t r o n s are produced by i o n i z a t i o n cf hydrogen H(is) + A J - >H + +e ( 1) These f r e e e l e c t r o n s c o l l i d e with each o t h e r , s e t t i n g up a Maxwellian v e l o c i t y d i s t r i b u t i o n , and a l s o with heavy elements, causing the e x c i t a t i o n of these elements to metastable l e v e l s from which t h e , c o l l i s i o n a l l y e x c i t e d l i n e s > t are produced. The net r e s u l t i s t h a t f r e e , e l e c t r o n s l o s e energy and can be recaptured e a s i l y by protons. T h e r e f o r e , recombination and c o l l i s i o n a l e x c i t a t i o n frcm the ground s t a t e 10 are the processes r e s p o n s i b l e f o r the e m i s s i o n - l i n e s p e c t r a i n nebulae. The observed spectrum i s thus produced by cascade t r a n s i t i o n s -*• H , + JU . <21 and by c o l l i s i o n s For the case of a w e l l observed b r i g h t p l a n e t a r y nebula, f o r t y or more l i n e s may be observed i n the recombination l i n e s p e c t r a of H°, Heo, and He+, while most observed c o l l i s i o n a l l y e x c i t e d l i n e s are due to t r a n s i t i o n s i n c o n f i g u r a t i o n s p 2 , p 3 , and p*. The f a c t t h a t these e x c i t e d l e v e l s have the same (n,L) c o n f i g u r a t i o n as that o f the ground s t a t e , makes these t r a n s i t i o n s f o r b i d d e n f o r e l e c t r i c .dipole and guadrupole r a d i a t i o n . . T h e r e f o r e , a l l of the c c l l i s i o n a l l y e x c i t e d l i n e s observed i n the o p t i c a l r e g ion are f o r b i d d e n l i n e s , w h i le the recombination l i n e s are permitted, , As a r e s u l t , i t i s customary i n ' nebular work to a s s i g n the same meaning to permitted or recombination l i n e s on one hand and f o r b i d d e n or c c l l i s i o n a l l y e x c i t e d l i n e s on the other.„ Now, the energy emitted i n a l i n e i s given by 11 m w U T f m mem m«v, ( 4) where Nn i s the number d e n s i t y i n the upper l e v e l of the t r a n s i t i o n i n v o l v e d , and Anm, i s the r a d i a t i v e t r a n s i t i o n p r o b a b i l i t y . Thus, we expect t o observe an i n t e n s i t y g i v e n by Eq. (4) i n t e g r a t e d over the l i n e o f s i g h t : = f e j 4 ( 5) provided t h a t the nebula i s o p t i c a l l y t h i n i n the observed l i n e , and no i n t e r s t e l l a r e x t i n c t i o n i s present. Since h and Anm are p h y s i c a l c o n s t a n t s , , the i n t e n s i t y o f a l i n e i s determined when the number d e n s i t y of the upper l e v e l i s known. The s t e a d y - s t a t e c o n d i t i o n i s used t o o b t a i n Nn. „ For example, the Balmer decrement i s given by -^mj, ^ m z hlm = ; ( D) I t i s a l s o p o s s i b l e t o c a l c u l a t e decrements f c r other s e r i e s or r e l a t i v e i n t e n s i t i e s o f l i n e s belonging to d i f f e r e n t s e r i e s . For example, B r o c k l e h u r s t ( 1 9 7 0 , 1 9 7 1 ) c a l c u l a t e d 12 decrements f o r hydrogen and helium t a k i n g i n t o account up t o 300 (hydrogen) and 40 (helium) l e v e l s . His r e s u l t s showed t h a t the dependence of the decrements on temperature i s s m a l l and made p o s s i b l e a comparison of observed and t h e o r e t i c a l decrements. In g e n e r a l , the observed Balmer Decrement i n most nebulae agrees q u i t e well with the t h e o r e t i c a l one ( M i l l e r 1972),, However, d e v i a t i o n s e x i s t , e.q, the observed r a t i o I(Hc()/I(Hp) i s g r e a t e r than the t h e o r e t i c a l one, and such d e v i a t i o n s are e x p l a i n e d by t a k i n g i n t o account i n t e r s t e l l a r e x t i n c t i o n . For the case of c o l l i s i c n a l l y e x c i t e d l i n e s , we a l s o have a s i m i l a r s i t u a t i o n to the one j u s t d i s c u s s e d : i t i s necessary t o determine f i r s t the p o p u l a t i o n of the e x c i t e d l e v e l s . Again, s t e a d y - s t a t e c o n d i t i o n i s used f o r determining the p o p u l a t i o n of the upper l e v e l j The g e n e r a l s i t u a t i o n i s represented by a t w o - l e v e l atom,, In t h i s case ( 7) % i =^ e K / l 3.2. ; — ( 8 ) where Anm i s the r a d i a t i v e t r a n s i t i o n p r o b a b i l i t y , and q i s the c o l l i s i o n t r a n s i t i o n p r o b a b i l i t y ^ 13 Formula (7) can be c o n s i d e r e d i n two l i m i t s : i ) For q„ Ne >> Anm = * r f ( - £ * . / K e ) ( 9) J . = ^ H 2 1 J (10) ITT s i n c e c o l l i s i o n s are dominant; w-j- i s the s t a t i s t i c a l weight of the l e v e l j . i i ) For q Ne << Anm hi, Az i - M u - ^ k - « 12) The g e n e r a l case i n gaseous nebulae i s somewhere between these two l i m i t i n g cases. For example, the i n t e n s i t y r a t i o of a u r o r a l to nebular forbidden t r a n s i t i o n s of a given ion ( I 3 2 . / I 2 i ) i s going to be a f u n c t i o n of both e l e c t r o n d e n s i t y and temperature, s i n c e one t r a n s i t i o n may be i n s i t u a t i o n i ) and the other i n s i t u a t i o n i i ) . . I f both t r a n s i t i o n s are i n case i i ) the I / I Z ( r a t i o i s very s e n s i t i v e to Te, but independent of Ne. I f one t r a n s i t i o n i s i n case i ) and the 1 4 other i n case i i ) and the two t r a n s i t i o n s have the same e x c i t a t i o n p o t e n t i a l , then the r e l a t i v e i n t e n s i t i e s w i l l not depend upon Te, but only Ne. iConseguently, f o r each observed a u r o r a l to nebular r a t i o a d e n s i t y versus temperature curve may be c o n s t r u c t e d . S e v e r a l of these r a t i o s f o r the.same o b j e c t should give c u r v e s with a common i n t e r s e c t i o n corresponding t o the l o c a l value of Ne and Te. . In appl y i n g t h i s method a c o n s t a n t e l e c t r o n d e n s i t y and temperature througout the nebula i s assumed. In p r a c t i c e , a unique s o l u t i o n i s not found and since the o b s e r v a t i o n a l e r r o r s produce d i f f e r e n c e s s m a l l e r than the ones present i n the [Te^Nei] s o l u t i o n s , i t f e l l o w s t h a t the hypothesis of c o n s t a n t Te and Ne i s not c o r r e c t and temperature and d e n s i t y inhomogeneities have to be taken i n t o account when s t u d y i n g the p h y s i c a l c o n d i t i o n s i n these o b j e c t s . 1 5 1 , 4 EXTINCTION TO PLftNET&RY NEBULAE I n t e r s t e l l a r extinction i s a process that follows a law of the form: where I0(>) i s the i n t e n s i t y that would be observed at the earth sight, l(>)is the i n t e n s i t y observed, and x>> i s the o p t i c a l depth at the wavelength observed.. Extensive s t e l l a r photometric work dene over the years has shown that, to a good approximation, the form of the wavelength dependence of the i n t e r s t e l l a r extinction i s the same throughout the galaxy, and only the amount of extinction varies from place to place. Therefore, the opti c a l depth, T A , can be expressed as ( 7) i n the absence of i n t e r s t e l l a r extinction along the l i n e of ( 8) where k i s a constant factor depending on the object observed and the function f (^ ) i s the same for a l l objects. 16 The n o r m a l i z a t i o n of the f u n c t i o n f (>0 i s a r b i t r a r y . . The no r m a l i z a t i o n adopted i n nebular work t a b u l a t e s f (>>) T f (Hp) , so i t i s easy t o c o r r e c t a l l e m i s s i o n - l i n e r a t i o s i n v o l v i n g Hp, the usual nebular standard l i n e . T h e r e f o r e , • • I f Hp) £ o (Hp) < 9 ) = *« ( ^ <W[-c[J(>,-](Hp)}] . i o (Hp) where the constant c, c = . 4 3 4 k , i s the t o t a l e x t i n c t i o n at Hp and f ( > i ) - f ( H p ' ) i s the standard i n t e r s t e l l a r e x t i n c t i o n curve, expressed r e l a t i v e to the e x t i n c t i o n a t Hp, and normalized so th a t f(<*>) = - 1 , and f (Hp) = 0 , The e x t i n c t i o n at Hp i n magnitudes i s then, AHp = 2 £c (10) Three methods have been used t o estimate the e x t i n c t i o n toward p l a n e t a r y nebulae: i ) Comparison of the measured r a d i o emission t o the Hp f l u x (Higgs 1971 ) 17 i i ) Use of the i n t e r s t e l l a r e x t i n c t i o n "bump" at 2200 A (Pottash et a l . . 1976) i i i ) Comparison of observed and t h e o r e t i c a l o p t i c a l l i n e r a t i o s In the o p t i c a l r e g i o n , the e x t i n c t i o n c o n s t a n t , c, can be found i f there i s a l i n e i n t e n s i t y r a t i o which can be t h e o r e t i c a l l y p r e d i c t e d . The best l i n e s would be a p a i r with the same upper l e v e l , because i n t h i s case the i n t e n s i t y r a t i o would depend only on the r a t i o of the r e s p e c t i v e t r a n s i t i o n p r o b a b i l i t i e s . A good example i s the f o u r i n f r a r e d £SII] l i n e s at >^  10330A. These l i n e s have the same upper l e v e l as the blue 4068, 4076 [ S I I ] l i n e s , t h e r e f o r e t h i s method has nc dependence on the p h y s i c a l c o n d i t i o n s i n the nebula. U n f o r t u n a t e l y the l i n e s i n v o l v e d are weak ones, the i SII jj i n f r a r e d l i n e s s u f f e r from airglow contamination, and there are no d e t e c t o r s with a good response over such a wide s p e c t r a l r e g i o n . An e a s i e r o b s e r v a t i o n a l method has been the use cf Baimer l i n e s and, when p o s s i b l e , Paschen/Balmer r a t i o s . For example, r a t i o s Ho</Hp, H p / H ^ , and Paschen l i n e s from l e v e l s 6, 7, up to 19 have been e x t e n s i v e l y used f o r t h i s purpose. T h e o r e t i c a l 18 l i n e r a t i o s are taken from B r o c k l e h u r s t , Case B (1971).. Ob v i o u s l y , the Balmer l i n e s are the ones used most f r e q u e n t l y , because these l i n e s are strong and i n a p a r t of the spectrum where most d e t e c t o r s show a good response. For b r i g h t o b j e c t s with a r i c h spectrum t h e r e i s a l s o the p o s s i b i l i t y of d e t e r n i n i n g the e x t i n c t i o n c o n s t a n t , c, from other, more "unusual", l i n e r a t i o s . For i n s t a n c e , f o r the p l a n e t a r y nebulae NGC 7027, K a l e r et a l . (1976a) have d e r i v e d the e x t i n c t i o n constant, c, from the l i n e r a t i o s J.SII| 10330/ 4070, £ S I I I J 6312/ 3721, Ha/Hp, Hy/Hp , H5/Hp , P 6/H^, P.,/Hp, Hel 5876/ 4471, H e l l P f / P i 8235/ 4541, and the radio/Hp (Te ~ 11500K ),. . I t i s important to r e a l i z e t h a t the use cf the e x t i n c t i o n c o n s t a n t , c, f o r determining the e x t i n c t i o n i m p l i e s knowledge of the shape of the f u n c t i o n f ( M . I f we d e f i n e a c c l o r excess as ri(m-Up) = W W ^ l (11) then the e x t i n c t i o n towards the nebula may also be d i s c u s s e d 19 as a f u n c t i o n of t h i s parameter. M i l l e r e t a l . (1972) were among the f i r s t to p o i n t out t h a t t h i s c o l o r excess, E (H<* -Hp) , and the e x t i n c t i o n constant, c, are independent parameters and t h a t E(H<* - Hp) , c, and R are r e l a t e d by the assumed " u n i v e r s a l " e x t i n c t i o n by the r e l a t i o n 0. «fc3 Hot - Hp) This can be shown t c be t r u e by the f o l l o w i n g r e a s o n i n g : the p r e s e n t l y used e x t i n c t i o n curve has two segments n e a r l y l i n e a r i n i n v e r s e wavelength, with the break p o i n t at about 4400A,. T h e r e f o r e , t h i s law i s u s u a l l y expressed i n terms of > - i with the n o r m a l i z a t i o n , f (>-») = E (A - V)/E(B - V), where E ( i \ . - > z) = " A>j denotes the c o l o r excess a t wavelengths )ii and \ . . A l s o , f(0) = -Av/E(B -e f f e c t i v e f i l t e r wavelengths 1. 8 3 ^ - i , Then, assuming a l i n e a r curve f o r wavelengths longward - V), can be approximated from V) = -R = -2.97, based on the = 2.29^ - i and > v-» = approximation t o the e x t i n c t i o n of 4400A, the c o l o r e x c e s s , E(B any one Balmer c o l o r excess. 20 For example, see F i g u r e 1 , E (B - V) = 0 .863E(H<K - H^ ) and &v = A H ( 3 - 0 . 4 2 5 E ( H o ( - H(3) , _ 2 1 F i g u r e 1 L i n e a r Approximation to E x t i n c t i o n Curve 22 F i n a l l y , l e t us ask o u r s e l v e s how accurate a l l these d i f f e r e n t methods a r e . . Pottasch et a l . (1976) have presented values of E(B - V) f o r p l a n e t a r i e s , d e r i v e d from the "bump" a t 2200A, which are u n c e r t a i n at the most by about 0.04mag.t He has compared h i s data with the observed r a t i o Badic (6cm)/F (Hp) showing t h a t there i s a good c o r r e l a t i o n between these two parameters, when t a k i n g i n t o account the o b s e r v a t i o n a l u n c e r t a i n t i e s and even the dependence o f the r a t i o Badio/H^ on e l e c t r o n temperature, Te, and helium abundance. The agreement between the radio/Hp and "bump" a t 2200A methods with the Balmer l i n e - r a t i o i s not so good . I t i s important to emphasize t h a t t h i s d iscrepancy may be r e a l because the t h e o r e t i c a l c o n s i s t e n c y of these methods i s net i n guest i o n and the three of them only give a weighted average f o r the e x t i n c t i o n over the whole nebula. T h e r e f o r e , i t i s p o s s i b l e t h a t non-uniform, p a r t i a l o p t i c a l o b s c u r a t i o n could e x p l a i n the observed difference,. . In ether words, l a r g e u n c e r t a i n t i e s may appear i n the o b s e r v a t i o n s due t o v a r i a b l e e x t i n c t i o n across the face of the nebula. T h i s i s a known s i t u a t i o n i n HII Eegions and M i l l e r et a l . (1972) have shown t h a t v a r i a b l e e x t i n c t i o n i s observed i n NGC 7027,. In g e n e r a l , v a r i a b l e i n t e r s t e l l a r e x t i n c t i o n across the f a c e of a nebula w i l l l e a d t o a value of E which i s h i g h e r 23 than the one t h a t r e a l l y c h a r a c t e r i z e s the o b s c u r i n g m a t e r i a l . T h i s i s t r u e because the d e r i v e d e x t i n c t i o n i s weighted by the most obscured p a r t of the nebula, while the d e r i v e d c o l o r excess i s weighted by the e m i t t i n g r e g i o n . . T h e r e f o r e , M i l l e r ' s r e s u l t of E = 3-47 f o r NGC 7027 has to be c o n s i d e r e d as an upper l i m i t . 24 1-5 THE PROGRAMME As i t i s i n most areas of s c i e n t i f i c r e s e a r c h , the study of these o b j e c t s has been paced by the i n s t r u m e n t a t i o n a v a i l a b l e at the time of the o b s e r v a t i o n s . A - l a c k of d e t e c t o r s with s u i t a b l e s e n s i t i v i t y i n the red and near-i n f r a r e d r e g i o n s has r e s t r i c t e d most of the study of d i f f u s e nebulae t o the blue- v i s u a l r e g i o n cf the spectrum. Information r e g a r d i n g many important l i n e s i s thus m i s s i n g , e.g. Paschen l i n e s of hydrogen, and t r a n s i t i o n s of J.SIIH], £SII], [ O i l ] , [ 0 1 ] , [ C I V ] , [ N i l ] , and [ Nl ] ( A n d r i l l a t e t al._ 1S75) . . In the past few years, s o l i d - s t a t e image sensors (CCD and CID's) combined with computer c o n t r o l and a proper p i c t u r e -p r o c e s s i n g code has opened up the p o s s i b i l i t y of g a thering a s t r o n o m i c a l i n f o r m a t i o n using systems t h a t o f f e r high-guantum e f f i c i e n c y between 6000 and 10000A, a l a r g e dynamic range, and an almost l i n e a r response.. As they can be used as one-or two-dimensional d e t e c t o r s , they are becoming i n c r e a s i n g l y important f o r the study of extended o b j e c t s . They hold great promise f o r mapping the monochromatic surface b r i g h t n e s s d i s t r i b u t i o n s and f o r spectrophotometric s t u d i e s of p l a n e t a r y nebulae and HII r e g i o n s . These .observations are important 25 s i n c e p r e v i o u s photographic and e l e c t r o n o g r a p h i c s t u d i e s have shown that even the most uniform of these o b j e c t s shows a complicated e x c i t a t i o n s t r u c t u r e ( A l l e r e t a l , 1970). Khromov (1976) made an a n a l y s i s of the p r e c i s i o n of the spectrophotometrie data a v a i l a b l e f o r p l a n e t a r y nebulae. He concluded t h a t when d e a l i n g with an average s p e c t r o p h o t o m e t r y r e s u l t , the p r e c i s i o n of the a v a i l a b l e data i s low, He f i n d s t h a t i n the wavelength range 3700-10830A, the mean e r r o r (%) of a s i n g l e p u b l i s h e d i n t e n s i t y of a s p e c t r a l l i n e i s no b e t t e r than 32 per c e n t f o r the s t r o n g e s t l i n e s i n the b r i g h t e s t o b j e c t s . L i n e blends are a l s o a s e r i o u s problem. For example, there a r e q u i t e a number of o b s e r v a t i o n s i n which the [ N i l ] 6548,6584A l i n e s are blended with 6563A (Kaler e t a l ^ 1976b), This doublet i s temperature s e n s i t i v e , thus i s important t h a t l i n e r a t i o s o f t h i s i o n (or £ SIII J 9065,9532A) be observed, as they a r i s e from d i f f e r e n t r e g i o n s of the nebula than the £OIIIJ 4959, 5007A d o u b l e t , which i s the most observed doublet of t h i s type. . ' The [ N l l f ] doublet i s a l s b a good i n d i c a t o r of the e x c i t a t i o n c o n d i t i o n s i n the nebula., Hawley e t a l . (1977) have shown t h a t i n NGC 6720 (the Ring nebula) the {. N i l j are 26 enhanced near the edge of the nebula as r e s u l t of n i t r c g e n being nearly a l l N i l i n these r e g i o n s . . A l s o , these l i n e s show a very e r r a t i c behaviour. They are strong (as compared with the H« 6563 l i n e ) i n IC 418 ( l o w - e x c i t a t i o n planetary) and NGC 6741 ( h i g h ^ e x c i t at i o n planetary) and very weak i n p l a n e t a r i e s l i k e NGC 6826 (l o w - e x c i t a t i o n ) and NGC 3242 ( h i g h - e x c i t a t i o n ) . In NGC 2392, an extremely inhomogeneous p l a n e t a r y , the b r i g h t e r , i n n e r r i n g shows strong J. N i l d while the f a i n t e r , outer r i n g shows str o n g £NIJ emission. Other l i n e s of gr e a t i n t e r e s t i n the n e a r - i n f r a r e d spectrum of emission nebulae are the *Dt (9069,9532A) f o r b i d d e n t r a n s i t i o n s of S I I I . In p a r t i c u l a r , the 9532 A l i n e i s very i n t e r e s t i n g because: i) i t has an o p t i c a l p e n e t r a t i o n through dust twice as f a r as Hc(. i i ) i t i s expected t h a t S I I I i s the acst common stage of i o n i z a t i o n f o r s u l f u r . i i i ) i t i s the t h i r d s t r o n g e s t l i n e i n the s p e c t r a o f emission nebulae ( a f t e r Ho( and the green [ O I I I J l i n e s ) . Only very r e c e n t l y (Barker 1S78c) has spectrophotometry been reported a t t h i s wavelength. However, the s p a t i a l d i s t r i b u t i o n of the J . S I I I J ] emission remains almost unknown. Isophotes f o r only two p l a n e t a r i e s (NGC 40 and NGC 2392) have 27 been published a t t h i s wavelength ( A n d r i l l a t et a l . 1976). The comparison of the observed and t h e o r e t i c a l decrements of hydrogen permits the e v a l u a t i o n of the i n t e r s t e l l a r e x t i n c t i o n toward the nebula.. I f two-dimensional hydrogen l i n e s o b s e r v a t i o n s are a v a i l a b l e , the problem of p a r t i a l o b s c u r a t i o n over the f a c e of the nebula can be s t u d i e d i n d e t a i l . T h i s i s a known s i t u a t i o n f o r HII Regions, but f o r p l a n e t a r y nebulae the s i t u a t i o n i s not so c l e a r . There i s evidence of p a r t i a l o b s c u r a t i o n a c r o s s the face of the nebula f c r only one p l a n e t a r y , NGC 7027 ( M i l l e r e t al.. . 1972).. The comparison of the observed and t h e o r e t i c a l Paschen decrements of Hydrogen, and the Pfund decrements of H e l l gives i n f o r m a t i o n r e g a r d i n g the value of the e l e c t r o n d e n s i t y i n the i n n e r p a r t of the nebula., Kaler e t a l . (1976) have r e p o r t e d a value of Ne ~< 10 7cm - 3 f o r NGC 7027 from o b s e r v a t i o n s of these two decrements.. C o n s i d e r i n g that t h i s r e s u l t does not agree with e l e c t r o n d e n s i t y measurements made i n t h e . r a d i o r e g i o n (Chaisson e t a l . 1976) and a l s o does not agree with t h e o r e t i c a l p r e d i c t i o n s (Pequignot et a l . 1978), i t i s f e l t t h a t t h i s o b s e r v a t i o n s h c u l d be repeated, e s p e c i a l l y i f new o b s e r v a t i o n s can be obtained at a much higher r e s o l u t i o n than any work done i n the past. 28 T h e r e f o r e , i t was proposed to undertake the f o l l o w i n g program: i ) Spectrophotometry of compact nebulae i n the s p e c t r a l r e g i o n 6000-10000A at a d i s p e r s i o n cf 70-120 Amm-1, I t was hoped t h a t such measurements would produce i n f o r m a t i o n r e l a t e d to the p h y s i c a l c o n d i t i o n s of the gas, amount of i n t e r s t e l l a r e x t i n c t i o n , and a l s o would f i l l an obvious gap i n present measurements of r e l a t i v e l i n e i n t e n s i t i e s (Kaler et a l . 1976b),. Data obtained f o r t h i s purpose i s presented i n Chapter I I , but i t should be p o i n t e d out t h a t t h i s part of the program was never completed due t o poor weather c o n d i t i o n s , i n s t r u m e n t a l f a i l u r e s , and/or candid a t e ' s mistakes. T h i s goal was achieved f o r only one o b j e c t , NGC 7027, and the a n a l y s i s of i t s data i s presented i n Chapter I I I . . i i ) D i r e c t photography of p l a n e t a r y nebulae through narrow-band i n t e r f e r e n c e f i l t e r s , e. g. . 4861, 6563, £NIIj} 6584, and {_SIIIiJ 9532 y i e l d i n g i n f o r m a t i o n r e g a r d i n g the d i s t r i b u t i o n of the i n d i v i d u a l ions and e x t i n c t i o n by dust i n the nebula. T h i s p a r t of the program was f u l l y accomplished and four p l a n e t a r y nebula, NGC 2440, NGC 3132, NGC 3242, and NGC 7027 were s e l e c t e d f o r a d e t a i l e d study. A l l of them have s e v e r a l f e a t u r e s of i n t e r e s t . . For example, NGC 2440 and NGC 7027 both have an i r r e g u l a r o p t i c a l appearance, no c e n t r a l 29 s t a r i s v i s i b l e , and both have a very r i c h spectrum. NGC 3242 shows very weak [NIK] emission (the opposite from NGC 2440) , NGC 3132 has a b i n a r y system as c e n t r a l s t a r (Kohoutek e t a l . 1977) and because of i t s f a r south d e c l i n a t i o n has not teen observed as much as other p l a n e t a r i e s . . The f c u r of them are b r i g h t o b j e c t s , with a l a r g e range i n i n t e n s i t y i n t h e i r spectrum, a l l o w i n g us to take f u l l advantage of the l a r g e dynamic range of the type of d e t e c t o r s used f o r these o b s e r v a t i o n s . The a n a l y s i s of the two-dimensional data f o r NGC 70 27 i s presented i n Chapter I I I . Chapter IV p r e s e n t s a s i m i l a r a n a l y s i s f o r the r e s t of the p l a n e t a r i e s . . Chapter V summarizes the r e s u l t s and d i s c u s s e s the work t o f o l l o w t h i s r e s e a r c h . The present a v a i l a b i l i t y o f multi-element image sensors, e.g. The UBC Diode Array System and the JPL 400x400 CCD camara makes a program of t h i s type a f e a s i b l e one. . Because of the volume and complexity of the output generated by t h i s type o f d e t e c t o r , the a n a l y s i s of t h i s type cf a s t r o n o m i c a l data i s done through a computer-coupled p i c t u r e p r o c e s s i n g . T h e r e f o r e , i t f o l l o w s t h a t the development of proper and e f f i c i e n t r e d u c t i o n techniques i s as important as the development of the d e t e c t o r s themselves. . Appendix I p r e s e n t s 30 a summary of the software package developed f c r the r e d u c t i o n and a n a l y s i s of t h i s type o f data. ., 31 I I . . OBSERVATIONS AND DATA REDUCTIONS 2. 1 SOLID STATE IMAGING DEVICES The i n t r o d u c t i o n i n 1967 of the concept of charge-coupled devices ty Weckler i n i t i a t e d a p e r i o d of r a p i d development f o r s o l i d - s t a t e image sensor technology. . Since then, photosensor a r r a y s have developed to the p o i n t where they have a p p l i c a t i o n s t o a wide v a r i e t y of e l e c t r o - o p t i c a l systems. At t h i s w r i t i n g , there are only two kinds c f these a r r a y s commmercially a v a i l a b l e : the i n t e g r a t e d , d i o d e - a r r a y (IDA) and the charge- coupled or c h a r g e - i n j e c t i o n device (CCD or CID),. The way t h a t the photo-charge i s read-out d i s t i n g u i s h e s one device frcm the other.. Diode a r r a y s are read-out s e r i a l l y v i a MCS switches onto one or more video l i n e s while CCD's are read-out v i a analogue s h i f t r e g i s t e r s . , Up to 1978, only one-and-two dimensional i n t e g r a t e d diode arrays produced by E e t i c c n C o r p o r a t i o n , Sunnyvale, C a l i f o r n i a have had a s t r o n o m i c a l a p p l i c a t i o n s , , The f i r s t ones by T u l l 32 and Nather (1973) i n a s t r o n o m i c a l spectroscopy and Smith(1975) and L i v i n g s t o n (1975) i n s o l a r r e s e a r c h . , L i v i n g s t o n (1976) presented a review of the use of i n t e g r a t e d diode a r r a y s i n astronomy. CCD's, on the other hand, have been a v a i l a b l e only i n s p e c i a l circumstances t o the a s t r o n o m i c a l community. T h i s t h e s i s i s based on data obtained with both types of d e v i c e s : i n t e g r a t e d diode a r r a y s , the OBC Diode Array System, and a charge couple d e v i c e , a Texas Instrument 400x400 p i x e l format developed by the J e t P r o p u l s i o n L a b o r a t o r y , Pasadena, C a l i f o r n i a . 1 i ) T h e DBC Diode Array System At the U n i v e r s i t y of B r i t i s h Columbia, diode array systems have come as second g e n e r a t i o n d e t e c t o r s based cn the experience obtained from the p r e v i o u s l o w - l i g h t - l e v e l t e l e v i s i o n cameras.. By the t i m e . t h a t the o b s e r v a t i o n s were taken (May 1974 to November 1976) t h e r e were f o u r systems based on r e f r i g e r a t e d E e t i c c n a r r a y s , three f o r spectroscopy and one f o r area photometry. . 33 Table I The DBC Diode Array Systems Mode of o p e r a t i o n Low-medium r e s o l u t i o n Spectroscopy (~120Amm-i) |. Medium r e s o l u t i o n S pectroscopy ("70Amm- i) h  Low r e s o l u t i o n Spectroscopy (^160Amm-i) High r e s o l u t i o n S pectroscopy 5Amm_l) Area photometry Coolant D r y - i c e D r y - i c e D r y - i c e L i q u i d Nitrogen D r y - i c e Detector Foe us EL 256 A/17 Schmidt camera EL 256 A/17 Schmidt camera BL 256 A/17 Wynne camera — + EL 1024 C/17 EA 50x50 — + Cas Coude Cas Cas + ~ t Coude Cas 34 A l l of these d e v i c e s operate as p-n j u n c t i o n photodetectors i n a photcn f l u x i n t e g r a t i n g mcde as d e s c r i b e d by Weckler (1967). In b r i e f , at the beginning of the exposure, the diodes are back biased t o a preset l e v e l 5 V o l t s ) . Absorption of incoming photons and thermal e f f e c t s produce e l e c t r o n - h o l e p a i r s . . The depth at which the p a i r i s formed depends on the energy of the incoming photon. The more e n e r g e t i c i t i s , the l e s s does i t penetrate. ,, These p a i r s d i f f u s e through the s i l i c o n and the min o r i t y c a r r i e r s on r e a c h i n g the d e p l e t i o n l a y e r d i s c harge the diode (2x10 7 c a r r i e r s w i l l completely d i s c h a r g e the d i o d e ) . At the end of the exposure, a s i n g l e s t a r t pulse i n i t i a t e s t h e . r ead-out sequence. Diodes are r e r b i a s e d i n sequence and the magnitude of the charge r e p l a c e d i s the measure of the exposure. The re c h a r g i n g c u r r e n t pulse i s converted to a v o l t a g e pulse, i n t e g r a t e d , d i g i t i z e d , and stor e d on magnetic tape. Complete d e s c r i p t i o n s of these array systems are found i n Buchholtz et a l . ( 1976), Walker et a l . (1976), and Mochnacki (1977) . 35 i i ) The CTIO-JPL CCD System The Texas Instruments CCD a r r a y used f o r our o b s e r v a t i o n s at CTIO was a part of a system made a v a i l a b l e to s e v e r a l American o b s e r v a t o r i e s by the J e t P r o p u l s i o n L a b o r a t o r y , Pasadena, C a l i f o r n i a - Our observing run a t CTIO was only the second time t h a t t h i s d e t e c t o r had been used (the f i r s t one being a t L i c k Observatory at the end o f 1977) . This p a r t i c u l a r c h i p was a back-side i l l u m i n a t e d CCD sensor. CCD a r r a y s are backside i l l u m i n a t e d t o e l i m i n a t e dead zones due to the p a t t e r n o f e l e c t r o d e s t h a t d e f i n e the photoelements, t o improve the blue s p e c t r a l response and t o all o w electron-bombarded or X-ray o p e r a t i o n . T h i s means t h a t the backside o f the c h i p has t o be thinned to b r i n g t h i s s u r f a c e near the CCD wells and minimize l a t e r a l d i f f u s i o n . T h i n n i n g , however, d i m i n i s h e s the response f o r wavelenths g r e a t e r than about 8000A.„ In our case, the extreme t h i n n e s s of the array (Ktyv) i s r e s p o n s i b l e f o r the severe f r i n g i n g superimposed on the s i g n a l f o r monochromatic o b s e r v a t i o n s with > >6000A. The CCD e l e c t r o d e s are biased so p h o t o e l e c t r o n s are c o l l e c t e d by the n e a r e s t photoelement. When the exposure i s over ( c o n t r o l e d by a shutter) a charge p r o p o r t i o n a l t o the 36 o p t i c a l image i s h e l d by the e l e c t r o d e s . . Ey s w i t c h i n g the vo l t a g e s a p p l i e d t o these e l e c t r o d e s , the charge i s t r a n s f e r e d element by element to an on-chip a m p l i f i e r where i t i s converted i n t o an output s i g n a l v o l t a g e . I t i s t h i s on-chip a m p l i f i e r which permits the very low read-out n o i s e of the CCD a r r ays. As we have already presented a f u l l d i s c u s s i o n of the o p t o e l e c t r o n i c c h a r a c t e r i s t i c s o f t h i s system (Fahlman et a l . 1978), only the most important performance parameters are presented below: i) The a r r a y had a number of d e f e c t s , i . e>. dead columns and p i x e l s . . The f i r s t twenty columns and ten bottom rows were u s e l e s s . We mainly use a f i x e d 200x200 p i x e l area which was c o s m e t i c a l l y the best area of the a r r a y . , i i ) The device was - used only f o r d i r e c t photography with exposures up to 10 minutes or l e s s through narrow and wide-pass f i l t e r s . i i i ) Wavelength response: we obtained data from about 4400 (B f i l t e r ) t o the Hel 10830 A l i n e . Response at B was about 30 per cent of peak response and a t 10830 A the response was about 1 per c e n t of peak; T h i s agrees r e a s o n a b l e l y w e l l with the expected s p e c t r a l response (Figure 2 Jr-L p r i v a t e communication). iv) F l a t f i e l d c a l i b r a t i o n and F r i n g i n g : These 37 two important c h a r a c t e r i s t i c s of the a r r a y are c o n s i d e r e d i n d e t a i l i n the next s e c t i o n , together with the r e d u c t i o n of the data . 38 3 9 F i n a l l y , Table I I presents a summary of the most s i g n i f i c a n t performance parameters of a l l the systems used i n t h i s r e s e a r c h program. They a l l have i n cemmcn the f e a t u r e s of high quantum e f f i c i e n c y and broad s p e c t r a l range t y p i c a l o f s i l i c o n d e v i c e s , they are very compact and have complete s p a t i a l s t a b i l i t y . . At low l i g h t l e v e l s , n o i s e i s dominated by read-out n o i s e while at high l e v e l s shot noise predominates. CCD"s show an extremely low read-out n o i s e , B e t i c o n ' s s u f f e r from a high read-out n o i s e . . A l l of them must be cooled t o l i m i t dark c u r r e n t . 40 Tabl e I I Performance Parameters For The D e t e c t o r Systems P ar am et er 1 256 , | 1024 | 50x50 |400x400 I Array I Array I Array | Array Array S i z e (mm) 1 6 | 25.6 I 5x5 | 9x9 Thickness (JJJ ) | 300 |300 I 300 | 10 Format | 256 | 1024 | 5 0x50 |400x400 P i x e l S i z e ( yj) 1 25.4 I 25.4 | 102 | 23 Dead Space | none | none | 50% I none S a t u r a t i o n 1 I 1 Charge ( c a r p i x - 1 ) | 1.2x107 |2.0x107 | 5,0x10*1 3.0x105 Head-out . j I 1 Noise (car r m s p i x - 1 ) J 20 00 ! | 360 0 | 4000 | 27 Operating 1 I 1 Temperature ( C) I -65 | -100 | -76 | -100 Dark C u r r e n t | 500 I n i l J 50 I n i l ( c a r s e c - 1 p i x - 1 ) ! I |' •! S p e c t r a l Range (nm) 1 I I (Q.E. >1%) 1 0.4-1-1 I0.4-1.1 | 0.4-1. 1|0.4-1.1 feak Q, E. . | 70% 1 70% 1 70% | 7 0% (at 0. 7nm) 1 1 I Maximum S/N | 1500 | 2500 | 250 | 5000 ( h a l f - s a t u r a t i o n ) j | { 4 1 2,2 SPECTROSCOPIC OBSERVATIONS i ) Line r a t i o s The s p e c t r o s c o p i c o b s e r v a t i o n s on which t h i s t h e s i s i s based were obtained using the UBC Diode Array System through the period May 1 9 7 4 to September 1 9 7 7 . , Table I I I g i v e s a few d e t a i l s of the i n d i v i d u a l o b s e r v a t i o n s while Table IV gives the nebulae f o r which data were obt a i n e d . A l l measurements :were made with the b r i g h t e s t spot of the nebula centered on the d e t e c t o r . The d e t e c t o r was not n e c e s s a r i l y centered on the s l i t . I t s exact p o s i t i o n was determined from scans o f a b r i g h t s t a r along the s l i t . No attempts were made to determine i n t e g r a t e d i n t e n s i t i e s of the nebular images.. A l l columns of Table I I I are s e l f - e x p l a n a t o r y with the e x c e p t i o n of Cclumn 3 which r e p r e s e n t s the d i f f e r e n t a r r a y systems by A, B, C, and D. These systems are d e f i n e d a t the bottom of Table I I I . 42 Table I I I Sp e c t r o s c o p i c o b s e r v a t i o n s r T 1 1 r 'T x 1 | Datei Obs. S p e c t r a l | D i s p e r s i c n | Pro j Comp. i i i i r e g i o n (A) | Adiode-i | s l i t s t a r r i |May74| DAO 1 1. 2m Coude — A 6300 - 9 0 0 0 J _ _ ^ _ _ _ 1.7 I 3.4 I * i y r |Jun74j DAO 1. 2m Coude A| 4800 - 8 5 0 t 1 | 1 - 7 l 3-4 I <>{ l y r |Aug74j MKO 2. 2m Cas A 6300 - 6 8 0 0 I 2.7 | 1,-4 I « l y r |Aug74| HKO 2. 2m Cas A| 9000-9500| 2-7 | 1. 4 | X Cas |0ct74| DAO 1. 2m Coude Aj 6000-8500| 1 ,-7 I 3-4 \Y Cas |Aug75| DAO 1. 8m Cas B | 6000 - 7 0 0 0 I 3-9 i 3.4 << l y r 1Sep75| BAO 1 . 8m Cas E 6 0 0 0 - 7 0 b 0 | 3,- 9 | 3.4 I << l y r |Nov75| DAO 1. 8m Cas B| 6000 - 7 0 0 0 I 3.9 | 3.4 I << l y r |Jan76| DAO 1. 8m Cas B| 6000-7000| 3-9 | 3.4 o( Lyr |Aug76| KPNO 2. 2m Cas C| 5700-70001 1.4 | 3.0 9Sgr |Nov76| DAO j 1. 8m Cas B| 57OO - 8 O 0 Q I 6.0 | 3.2 I )< Cas 1Sep77| DAO 1. 8m Cas D| 4800-109001 21.0 | 3,2 ^ C € t 1 ' I A = Schmidt camera + 256 dicde a r r a y B - Wynne camera + 256 diode a r r a y C = Schmidt camera + 1024 diode array D = Wynne camera * 1024 diode a r r a y Table I V Nebulae observed Planetary Nebulae | Object | Date | Tape | F i l e | Exp. | H. A. | Wavelength| L . i I-- L _ _ _ _ i sec j i * | ———-1 r e g i o n (A) j r ' | NGC I 40 | Nov75 | EA0499| r — — - * i 59 | — j — 2000| 2: r 47w| 6000-7000 | | NGC 40 | Nov75 | BA0499j 80 | 3000| 2: 43w| 6000-7000 | |IC 2003 | Nov75 | EA0499| 83 j 2000| 1: 0 5w| 6000-7000 | l i e 2149 | Nov75 | RA0499J 68 | 20001 2: 1 0w| 6000-7000 | l i e 2149 | Nov75 | EA0499I 89 | 30p6| 2: 06w| 6 000-7000 | I NGC 2392| Jan76 | EA0499I S8 | 1000| 2: 32w| 6000-7000 | | NGC 6543| Sep75 | BA0499I 175 j 500| 3: 30w| 6000-7000 | |NGC 6543| Sep75 | EA0499I 177 | 10001 4: 00w| 6000-7000 | | NGC 6572 | Aug75 | BA0499I 27 j 200 | 2: 00w| 6000-7000 | | NGC 7662| Sep75 | RA0499I 184 | 2000| 3: 05w| 6000-7000 | | NGC 7662| Sep75 | EG1075| 125 | 200 | 1: 23e| 5700-6800 | | NGC 7662| Sep75 | RG1075I 126 | 200 | 1: 23e| 5700-6800 | | NGC 7662| Oct76 | BG1075I 210 | 3000| 1: 02e| 6000-7000 | L  , J * = Hour Angle a t the beginning of the exposure Table IV(cont.) NGC 7027 h Date i r Tape — 1 - f 1 | Jun74 | BA0493I 27 | Jun74 | EA0493| 34 | Aug74 | EA0496I 50 | Aug74 | EA0496| 50 | Aug74 | BA0496| 178 | Oct74 | EA0493| 54 | Oct74 | EA0493| 150 1 Oct74 | EA0493| 154 | Oct74 | EA0493| 158 | Sep75 | BA0499I 178 | Aug76 | BG1075| 122 | Oct76 | BA0499J 202 | Oct76 | BA0499J 205 | Nov 76 | BA0499J 26 0 | Sep77 | BA0919] 539 | Sep77 | BA0919| 540 F i l e Exp, sec - + 500 500 150 1000 1000 500 400 1000 1500 1500 200 500 1000 2000 215 215 H. A • . * i ** ** ** 1:27w 1:38w 1:18w 1:04w 3:46w 4:42w 2:25w 1:31w 1:04w 2:03w 2:53w 1:07e 1:0 1e Wavelength region (A) H 6000-7000 7000-8000 6000-7000 9200-9850 8750-9350 4800-5200 6000-7000 9000-9300 9300-9550 5700-6800 57 00-6800 57 00-6800 5700-6800 7300-8800 4800-10900 4800-10900 ** Hour Angle at the beginning of the exposure Hour Angle and OT time of o b s e r v a t i o n net known Table I V (cont.) H I I Regions Object h~ I |NGC 1976 1 |NGC 1976 I |NGC 6523 I |NGC 6523 I |K3-50 I | K3-50 I IK3-50 I i | Date | Tape | F i l e j , Exp, | H.A. .| Wavelength | j . i _ _ _ _ _ X . sec| i * 1 r e g i o n (A) | i r j Nov75 | , . , 1 RA0499| J.. 63 | r 1000| l_. 0:03w| 6000-7000 | | Nov75 | RA0499| 64 | 2000| 1:00w| 6000-7000 | | Aug74 | RA0496J 41 | 2001 ** | 6000-7000 | | Aug76 | RG1075I 109 | . 200| 0:26wj 6000-7000 | | Aug74 | RA0496| 130 j 2500| 2:42wJ 6000-7000 | | Aug74 | RA0496| 17 2 | 2500| 1:23w| 9200-9800 | | Aug74 | RA0496I 183 | 2500| 3:36w| 8800-9300 | j L L j. • i ' j . j * = Hour Angle at the beginning of the exposure ** = Hour Angle and DT time of the o b s e r v a t i o n not known 46 The s l i t was kept f i x e d (e.g. east-west d i r e c t i o n f o r the Wynne camera a t DAO) and g u i d i n g was done on the b r i g h t e s t i spot of the nebula or on o f f - s e t s t a r s (when p o s s i b l e ) . A short and a long exposure i n each s p e c t r a l r e gion f o r each nebula was to be obtained, although i n some cases weather and/or i n s t r u m e n t a l problems d i d not allow t h i s g o a l to be accomplished i n a s a t i s f a c t o r y manner. The s t r o n g e s t l i n e , Hc(, was over-exposed (saturated) f o r the b r i g h t e s t o b j e c t s ( e. g. NGC 7027 and NGC 1S76) i n the long exposures, so the r a t i o s had to be determined with r e s p e c t to any f a i n t e r l i n e s ( e. g. £NIIJ 6584) and u l t i m a t e l y s c a l e d down to using the s h o r t e r exposure data. Although a d e t a i l e d e x p l a n a t i o n of the r e d u c t i o n procedure i s given i n the next s e c t i o n , l e t us point out t h a t : i) Observations are presented as r a t i o s between areas under th e l i n e p r o f i l e s because of changes of the s p e c t r a l r e s o l u t i o n across the f a c e of the d e t e c t o r . i i ) A p o s i t i v e . i d e n t i f i c a t i o n as an emission l i n e was given to a l l f e a t u r e s i n the s p e c t r a t h a t rose 2-3 standard d e v i a t i o n s above the n o i s e b a s e - l i n e . Airglow, c i t y l i g h t s , second-order blue contaminations and spurious B e t i c o n emissions were not i n c l u d e d i n the f i n a l l i s t of l i n e s . i i i ) L i n e - r a t i o i n t e n s i t i e s are presented 47 r e l a t i v e t o I ( H o ( ) = 100. . But, K3-50 data f o r >>8000A i s given cn a r a t h e r a r b i t r a r y s c a l e (I ( 9069) = 1. 00) because of a l a c k of data t h a t would allow a proper s c a l i n g to I ( H ) . . iv) E s p e c i a l l y i n the case of the lowest r e s o l u t i o n data (DAO: Wynne camera) the problem of blends a r i s e s . Blends have been i n d i c a t e d by b r a c k e t s . v) I = 0 means t h a t t h e l i n e was detected ( i , e. K 3 r ) , but no measurement of i t s s t r e n g t h was made. I =& means t h a t the l i n e has been observed.for the f i r s t time.. T h i s statement i s based on "A C a t a l o g of R e l a t i v e Emission L i n e I n t e n s i t i e s Observed i n P l a n e t a r y and D i f f u s e Nebulae" by James B. K a l e r (Ap.J.. Suppl.. 3J . , 517, 1976).. Table V presents the l i n e r a t i o s and b a s e - l i n e n o i s e , <r ., As the s c a l i n g procedure i s d i s c u s s e d i n the next s e c t i o n , the l i n e - r a t i o s f o r NGC 7027 are presented i n t h i s s e c t i o n . 48 Table V R e l a t i v e l i n e - r a t i o s P l a n e t a r y Nebulae 1 T IC 2003 2.9 I Object NGC I 40 1 <r rms I 1 .8 I | L i n e (A) 15755 I N i l 3 | 0.53 15876 Hel 1.39 | 6300 3. OU] 0 16312 t SIIIn] 0 | £435 t ArV,] | 6 548 i N i i g ' 25.65 16563 H<* 1 00.00 16564 t N i l 89.52 16678 Hel S 1.66 | 6717 L si J: 3 2.83 16731 t s i i ] 3.63 L  4.94 7.61 100.00 18.54 IC f NGC 2149 | 2392 1.8 | 2.8 0. 17 | 3.47j I 1. 14 i i i 5.06J 12.24 i 100.00J 100.00 I 14.69| 34.02 2. 18 j 0.81 II 0. 8 1 j i 2  33 3. 31 NGC | NGC | NGC 6543 i 6572 7662* 1.5 | 2,9 | 2.7 S 0.33 3. 18 100.00 9, 14 1.29 0.36 0.73 f ^ 7. 4 3 100.00 21.99 1.74 0,6 3 8. 16 0.68 0 10 0. 00 C fl.65 * = E r i g h t Ring, North of C e n t r a l Star Table V(cont.) HII Regions | Object | NGC | NGC | K3-50 | 1976*| 6523* 1 <T : cms 1 1-9 | 3.0 | 6.8 | Line (A) I 15755 XNII J I 0.16 7. 57 15876 Hel 1 2.43| 16300 [OIJ 1 0. 18 16212 £SIIIJ | 0-32 |6548 I N i l ] 1 6.05| 12. 43 l& 7,74 (6563 Ho( | 100.00 j 100.00 | 100.00 |6584 [ N i l j I 17. 85 j 29. 46 I 29> 12 |6678 Hel | 0.54| 16717 [ S I I J 1 1- 25 3.24 |& 4.86 16731 [ S I I J | 2.0 4 7.03 |S 6. 08 —A — L J * = B r i g h t spot Table V (cont.) K3-50 |8750 P12 8 0. 13 J8863 P11 S 0,07 19015 P10 S Oi 0 5 J9C69 J. SIII3 1.00 | 9229 P09 S 0!i 10 J9345 H e l l S 0.04 | 9 532 j; SIII,] 3. 17 | 9546 P08 S 0, 13 L \: 5 1 2.3 DAT REEuCTION The o v e r a l l procedure c o n s i s t s of the determination of the e m i s s i o n - l i n e s t r e n g t h s f o r each spectrum and (NGC 7027 only) a f i n a l s c a l i n g of those i n t e n s i t i e s t o I {Hoc) = 100. Each spectrum observed was smoothed with a 0.5 Nyguist f i l t e r (when necessary) and the r e l a t i v e l i n e s t r e n g t h s were obtained by i n t e g r a t i n g the s i g n a l over the i n t e r v a l of the l i n e and s u b t r a c t i n g a low order polynomial f i t t e d to the l o c a l continuum.. I t was not necessary t c perform a l e a s t -square f i t to the l i n e p r o f i l e because t h e r e i s no "dead-space" between the diodes; t h e r e f o r e a d i r e c t summation of the diodes' h e i g h t s g i v e s the l i n e strength,„ The i n s t r u m e n t a l response f u n c t i o n and the e f f e c t s of d i f f e r e n t i a l atmospheric e x t i n c t i o n were determined frcm the spectra of the comparison s t a r s observed as n e a r l y as p o s s i b l e at the same air-mass as the nebula and compared with the p u b l i s h e d f l u x e s of photometric standard s t a r s by Hayes (1970) and Hayes (1975) . . Allen(1973) atmospheric e x t i n c t i o n model was employed. Table I I I g i v e s the l i s t of comparison s t a r s used f o r each of the observing n i g h t s . 52 The wavelength s c a l e was determined frcm the o b s e r v a t i o n of s u i t a b l e comparison arc lamps through the night,. Formula (13) summarizes the ge n e r a l procedure f o r the i n s t r u m e n t a l response and atmospheric e x t i n c t i o n c o r r e c t i o n , where ( Urt) units) I ( * ) = observed i n t e n s i t y at wavelength 7> (ADC observed i n t e n s i t y at He< (ADC u n i t s ) I0(;\) = t r u e i n t e n s i t y at wavelength ^ (ADC units) I0(>) = true i n t e n s i t y at (ABC u n i t s ) T h e r e f o r e , mo(<) . =, + 2.5 T > iL e sec €> y, men men ° T h e r e f o r e , W o ( ' ^ - ft«»o(>| = « - f ^ R + 1 . 0 8 6 ^ ( s e c d f t t t - Sec. 5 3 or ! w 0 ( ^ . = w ( ) i ) + } r n i o ( > ) , - \+ 1 .096 T^(secQ - s e e © , ) (13) 1*8,9 n,ei> ' " L A° S+OR T h i s formula provides the b a s i c framework with which the s p e c t r o s c o p i c o b s e r v a t i o n s were reduced. As j u s t mentioned above, the r e d u c t i o n procedure f o r NGC 7027 c o n s i s t s of one f u r t h e r s t e p . ; A composite spectrum, from 5000 to 10000A, of t h i s p l a n e t a r y was obtained. Spectra were taken i n d i f f e r e n t , but o v e r l a p p i n g , s p e c t r a l r e g i o n s using d i f f e r e n t d i s p e r s i o n s . , Obviously, the higher r e s o l u t i o n d e v i ce (Schmidt camera) was used to d e r i v e mcst of the l i n e -r a t i o s , while the l o w - r e s o l u t i o n device (Wynne camera) provided .the necessary b r i d g e between s p e c t r a of high e r d i s p e r s i o n . . The Wynne camera was used a t three d i f f e r e n t d i s p e r s i o n s (3.9, 6.0, 21.0 A d i o d e - 1 ) and the lowest d i s p e r s i o n data (DAO September 1977) was used f o r t h i s purpose. Data from each scan w i l l d i f f e r from the others by an a r b i t r a r y s c a l e f a c t o r . T h i s s c a l e f a c t o r was determined from l i n e s present i n both s p e c t r a . In the s i t u a t i o n s when there were more than one l i n e present i n both s p e c t r a the s c a l e f a c t o r was determined from l i n e s f r e e of s a t u r a t i o n , underexposure or blend problems. Table V I I I shews the l i n e s 54 and s c a l e f a c t o r s used f o r each s e t of data. The f i n a l r e s u l t s f o r NGC 7027 are presented i n t a b l e VI... The wavelengths are from Kaler et a l . t (1976) and checked ; i l a g a i n s t the Revised M u l t i p l e Table (Mocre, 1945).. <I> rep r e s e n t s the f i n a l r e l a t i v e i n t e n s i t y cf t h e . l i n e . E r r o r means our best estimate f o r the f i n a l o b s e r v a t i o n a l e r r o r , and N gi v e s the number of i n d i v i d u a l o b s e r v a t i o n s from which <I> was d e r i v e d , 55 Table VI B e l a t i v e l i n e - r a t i o s : NGC 7027 r , Element | Kaler(1976) I <I> I E r r o r | 1 N | Notes| 9650 I c i 3 I 3.7E-1 | h 8.5E-2 | 1 I 9 623 i c i 3 j 1 i l. . - r l | 6. -2 | 1 | 1 I 9545 P08 j ; 1 3. 1 0 | 6.8 -1 I 2 I 9532 i S H I f l I 1-1.39E 2 | 6;46 1 | 2.6 0 | 2 I 9345 Hel I 1 2.3 0 I 6.4 -1 I 1 | 2 | 9229 P09 I 3.0 0 1 2 . 7 0 | 2 .4 -1 I 3 I 9069 i s m e | 2.46 1 I 2.48 1 | 1.9 0 I 2 I 9015 P10 | 1.80 0 | 1.48 0 | 3.4 -1 I 2 i 8863 P11 | 1.10 0 I 1-07 0 | 2. 3 -1 I 3 1 8751 P12 | 1 . 1 0 I 7.9-1 | 2. 1 -1 I 2 1 8727 IC I i ] I | 6.4 1 | 4.9 -2 | 1 | 8665 P13 I 5.0 -1 I 2l9 -1 | I f 1 9.6 - 2 | 1 | 8598 PI 4 | 3.8 -1 I 4.6 -1 | 1.3 ~ 2 | 2 I 8580 £ CLIIIj] I I o! i I I 8546 p i s I 4.2 -1 1 if 4 -1 i 6.8 -2 | 2 I 8503 P16 I 3.2 -1 I 3-48 -1 | 3.8 -2 | 1 I 8467 P17 | 2-2 -1 I i t 5.-1 | 2.4 -2 | 1 I 1 | 8446 i OH] | 1.3 -1 I r t iU -1 | 4. 6 — 2 | 1 I 8438 P18 I 1 - 9 -1 ! 1 ; I J 8413 P19 | 1-3 -1 I nj.6 -1 i 2.7 ~ 2 | 1 I 56 Table VI(cont.) _ 1 ~ 8392 P20 | 1.1 -1 I 1.1-1 I 2. 1 -2 | 1 1 3 8346 P23 j 5.9 -2 I j 1.2 -1 | 2, 5 -2 | 1 1 3 8334 P24 | 4.5 -2 ! 1 1 J | 8237 H e l l | 7-8 -1 1 8,0-1 | 1. 7 - 1 | 2 1 4 8196 LCLIIIi] | 2.7 -1 | 2.65 -1 | 9,6 -2 | 2 1 8088 I 5.2 -2 I 1.7 -1 | 1. 3 -1 | 1 i 1 8046 i c i i v g i 7.4 -1 I 710 -1 | 6,3 -2 | 3 1 7751 [ABIIIi] | 2.9 0 | 2.89 0 | 1. 3 -1 i 3 1 7726 I CIV.] | 1-4 -1 i 2.02 -1 | 1, 1 -1 | 1 1 7593 H e l l | 4. 1 -1 I 5.8 -1 1 1. 3 - 1 | 1 1 7531 i CLIV 3 | 2.6 -1 1 2.8 -1 | 3. 8 — 2 | 2 J 7380 I | 1,9-1 | ji 7.0 - 2 | 1 i 7330 I. o n jj | 6. 1 0 | 6,27 0 | 3. 1 -1 | 1 1 7320 I o n 3 | 7. 1 0 I 7i.58 0 | 3. 5 -1 | 1 i 7281 H e l l | 2 . 9 -1 I 2[L 9 -1 | i 1,0 -1 I 1 i 7263 [AEIVi] I 1.8 -1 1 14 9 -1 I 7- 4 - 2 | 1 i 7237 lABivg | 3.2 -1 I 1.9 -1 | 7. 2 -2 | 1 i 7178 H e l l | 5.4 -1 I 0 | I i 7136 J.ABIII3 | 9 . 9 0 I 9.83 0 | 4.8 -1 | 2 ! 7065 Hel | 3.0 0 I 2-95 0 | • ij , 1.4 -1 | 2 5 7 Table VI(cont.) "J" 7 0 0 6 [AKVJ | • 1 . 5 0 | 1 . 5 4 0 1 2 . 4 - 1 I 2 I 6 8 9 1 H e l l | 2 . 6 - 1 | 2 . 7 - 1 ' I 5 . 4 - 2 | 1 I 6 7 3 1 [ S I I ] J 1 . 4 0 | i ., ' i - 2 1 0 I 6 , 9 - 2 I I 6 7 1 7 I S I I J 1 6 . 0 - 1 | 5 | 5 - 1 I 5 . 8 - 2 | 3 1 5 6 6 8 3 H e l l 1 { J 2 l 4 6 - 1 i 3 . 8 - 2 | 2 1 6 6 7 8 Hel | M . 2 - 1 | 9 i 6 - 1 i 1 . 1 -1 I 3 | 6 5 8 4 I N i l ] 1 3 . 5 6 +1 | 2 . 9 9 + 1 i 6 . 2 - 1 I 4 1 6 5 6 3 Ho{ 1 1 0 0 . 0 0 | 1 0 0 . 0 o I 2 , 2 0 I 5 1 6 5 4 8 [ N i l ] | 1 . 1 2 +1 | 1 . 0 3 + i i 3 . 2 - 1 I 5 1 6 5 2 7 1 I 1 . 7 - 1 I 2 . 8 - 2 | 2 1 6 6 5 1 8 £MnVl] | I 1 . 4 - 1 i 4 . 7 - 2 | 1 | 6 6 4 6 2 1 3 . 2 - 2 | 0'' ! I I 6 4 3 5 [ ABV ] | 6 . 1 - 1 | 6 . 1 - 1 i 9 . 4 . - 2 | 3 I 5 6 4 0 6 H e l l | 8 , 9 - 2 | 1 . 3 - 1 i 4 , 3 - 2 | 2 I 6 3 9 3 £MnVJ | I 2 . 4 -I 1 i 7 . 4 - 2 I 1 I 6 3 7 1 s i n | 3 . 8 - 2 | 9 i 4 - 2 I 3 . 7 - 2 | 2 I 6 3 6 4 £ o i J 1 1 . 2 0 0 | 1 . 1 0 I 6 . 5 - 2 | 3 I 6 3 4 8 S i l l | 5 . 1 - 2 | 0 I I I 6 3 1 2 [ S i l l ] | 1 . 4 2 0 | i . 3 0 | 1 . 3 - 1 I 3 I 6 3 0 0 £ o i ] I 3 . 6 4 0 | 3 . 8 6 0 I 1 . 4 - 1 I 2 I 7 j ' 1 l__ !_ J T a b l e VI(cont.) l - T _ — - 1— l 6234 H e l l | 5.6 -2 I 6.5 -2 1 4,4 -2 | 1 6219 iMnvg j 3.8 -3 | 0 \ | 6171 H e l l | 3. 1 -2 I 7. -2 1 3.5 -2 J 1 6118 H e l l | 3.6 -2 I 5. -2 1 3.7 -2 | 1 6102 J. KIV,] I 1.3 -1 i »l I 6G74 H e l l I 3.2 -2 | 4. -2 1 3. 0 -2 | 1 6037 H e l l I 2.3 -2 j 5. -2 1 3.7 -2 | 1 6005 H e l l | 2.0 -2 | 0 1 j 5977 H e l l I 2.2 -2 | 0 1 I 5S53 H e l l | 1.7 -2 | 0 | J 5876 H e l l | 2.86 0 I 2.88 0 i 2. 5 -1 I 2 5£47 H e l l | 5.1 -3 | 0 1 j 5800 CIV | 9.6 -2 | 0 1 5776 i. MnVIi I I 0 J I 5755 i Nil,] I 1.23 0 I 1,51 0 1 2. 3 -1 I 2 5411 H e l l | 9.18 -1 I 6,57 -1 I 9.0 -2 | 1 5016 Hel I 1.4 -1 I Mi I 5007 J.OIII,] J 1.96 + 2 | <^  2. 555 2 1 ! 4S59 J. OIII] I 6.53 + 1 I i 59 Notes: Table VI 1 Barely d e t e c t a b l e 2 Large discrepancy among o b s e r v a t i o n s . . Value adopted i s based upon a b e t t e r f i t to t h e o r e t i c a l Ffund Decrement. Discrepancy must be due to the f a c t t h a t t h i s l i n e l i e s w i t h i n a t e l l u r i c a b s o r p t i o n band. 3 Very d i f f i c u l t t o determine the z e r o - p c i n t l e v e l . 4 Large di s c r e p a n c y among o b s e r v a t i o n s . 5 <I> obtained from weighted mean of the three h i g h e s t r e s o l u t i o n o b s e r v a t i o n s c n l y , 6 Line l i e s on the wing of 6548. 7 <I> obtained frcm the weighted mean of the Schmidt camera only. 60 2. 4 FSECISION OF THE MEASUREMENTS The main source of e r r o r i n the l i n e . i n t e n s i t i e s i s the o v e r - a l l read-out n o i s e . . Even f o r n i g h t s with o b v i o u s l y unstable observing c o n d i t i o n s the f a c t o r id , -Qy ) i n m e t S-TCR' equation (13) was u s u a l l y s m a l l enough t o assure t h a t the atmospheric e x t i n c t i o n c o r r e c t i o n was almost n e g l i g i b l e . For example, f o r the DAO o b s e r v a t i o n s of NGC 7027 i n September 1S75, an atmospheric c o r r e c t i o n o f the order of 0.003 i n the l o g a r i t h m was d e r i v e d at 5755A with the r e f e r e n c e l i n e being J.0III] 6364 s i t u a t e d near the center of the array. The e r r o r i n t r o d u c e d by the f a c t o r (m0(*)-m(>)' ) became important c n l y f o r l i n e s with a f r a c t i o n a l e r r o r <6 percent. The o b s e r v a t i o n a l e r r o r i n the i n t e n s i t i e s was d e r i v e d f o r each i n d i v i d u a l scan and the o v e r a l l probable e r r o r was estimated from the s c a t t e r of the i n t e n s i t i e s measured i n each scan around the mean value (when p o s s i b l e ) . . In g e n e r a l , the weaker l i n e s show a l a r g e r e r r o r because of a lower s i g n a l - t o - n o i s e r a t i o (the determination of the l o c a l continuum i s much more d i f f i c u l t ) . As the data from the DAO September 1S77 observing run r e p r e s e n t s a complete s e t ( i t covers the wavelength r e g i o n 6 1 between H p and 1 0 8 3 0 A . ) and was the b a s i s f o r the s c a l i n g of the other scans, i t w i l l be d i s c u s s e d f i r s t . For t h i s d a t a , we f i n d t h a t f o r l i n e s with I > 2 (in the s c a l e I ( H c ( ) = 1 0 0 ) the o b s e r v a t i o n a l e r r o r i s s m a l l e r than 1 1 percent. For l i n e s with 2 > I > 0 , 5 , the o b s e r v a t i o n a l e r r o r i s i n the range 1 1 - 2 5 percent, while l i n e s with K 0 . 5 have o b s e r v a t i o n a l e r r o r s of the order of 3 0 - 4 0 percent. Table V I I shows these r e s u l t s with more d e t a i l and F i g u r e 3 shows a comparison of our r e s u l t s with the ones presented ty K a l e r ( 1 9 7 6 ) . The agreement between h i s data and ours i s , i n ge n e r a l , good. The worst departure i s f o r the data p o i n t s numbered from 1 to 6 , which correspond t o the f o l l o w i n g wavelengths: 6 2 No. 1 £751 Paschen 12 2 8665 Paschen 13 3 8598 Paschen 14 4 8546 Paschen 15 5 £334 Paschen 24 6 5411 H e l l K aler et al.. (1976) have s t a t e d t h a t i n h i s data the •. i i n t e n s i t y of any Paschen l i n e f o r which ?>>8300A i s probably under estimated because i t i s almost im p o s s i b l e f o r him to l o c a t e the und e r l y i n g continuum. 6 3 64 gable VII E r r o r estimates < 1 1 $ | 11-252 30-5055 I Line I | Line I I Line I 19545 | I 8663 1.06 0| 6665 2.34 -19532 3 67. 701 8751 8,21 - 1 1 8598 5.34 -19229 2. 66| 8237 7.66 -11 8546 2.96 -19069 | 23.90| 8046 7.40 -11 19015 J I 6087 4.24 -11 17751 2. 89 | 5755 1-59 I1 J7330 13.50| j |7320 1 | j 1 17136 9.96| J J7065 2. 98| 1 |7006 1.67| 1 I6563 100.00| j 16312 | ! 1 |6300 ^  5.81| 1 15812 2.90| } 65 As the s e n s i t i v i t y of our system drops o f f r a p i d l y f o r wavelengths g r e a t e r than and l e s s than 5500A, we expect lower accuracy i n these s p e c t r a l r e g i o n s due to the l a r g e i n s t r u m e n t a l response c o r r e c t i o n i n v o l v e d . A l s o , the i n c r e a s e i n the t e l l u r i c H e0 a b s o r p t i o n i n the i n f r a r e d and the low d i s p e r s i o n used, make our measurements.in these.two s p e c t r a l r e g i o n s u n r e l i a b l e . T herefore, we w i l l c o ncentrate our e f f o r t s on the a n a l y s i s of the l i n e - r a t i c s f o r wavelengths with 5500-O<10000A. ' F i n a l l y , the comparison of our r e s u l t s and K a l e r * s f o r the [ S I I I J 9532,9069 l i n e s was not p l o t t e d because K a l e r ' s value f o r the r a t i o l ( 9532) / I (9069) =5. 0 i s o b v i o u s l y wrong, as t h e o r e t i c a l values c f 2.56 (Garstang 1968) and 2.43 (Foukal 1974) are found i n the l i t e r a t u r e . T h e r e f o r e , at t h i s p o i n t we have a s e t cf low d i s p e r s i o n data which covers the s t r o n g e s t l i n e s , and which a l s o o v e r l a p with the data s e t s obtained at higher d i s p e r s i o n . . In order to s c a l e together a l l t h i s data, we t r y to use the l i n e s with the s m a l l e s t o b s e r v a t i o n a l e r r o r (<11 percent, Table V I I ) . Almost always one or two of these l i n e s were present, p e r m i t t i n g the dete r m i n a t i o n of the r e l a t i v e s e n s i t i v i t y of the two s e t s of data., In a couple of cases t h i s goal was net p o s s i b l e and l i n e s with wavelengths at 8862, 8232, and 8046A were used 66 f o r t h i s purpose. Table VIII shows the l i n e s and s c a l i n g f a c t o r s used f o r each s e t of data.. 67 Table VIII Sc al i n c j f a c t o r s : c 1 — — T~ |Wavelength| c | S c a l i n g | Observatory I r e g i o n | i i _ I l i n e s | 1 1— 19850-9229 \ 1.56 .j j 9545,95321 MKO:Schmidt 19229-8751 j 3.59 18863 | MKC:Schmiat | 9850-9345 I 1. 54 |9545,9532| DAO:Schmidt 19229-9015 | 4.45 |9069,9015| DAO:Schmidt |8237-8046 | 118.76 |8237,8046| DAO:Schmidt I8727-7325 | 34.44 |7751 | DAO:Wynne 17751-7531 | 34. 60 |7751 | DAO:Schmidt I7381-7G65 | 10.31 17325,7136 j DAO:Schmidt |7C65-6678 | 85,71 |6731,6717| DAO:Schmidt 16731-5755 | 76.55 15876 | DAO:Wynne { | C o n s i d e r i n g t h a t the s c a l i n g f a c t o r s were only c a l c u l a t e d from one or two l i n e s , i t was net p o s s i b l e to d e r i v e a mean e r r o r due to the s c a l i n g process while f i t t i n g one s e t of ob s e r v a t i o n s t o another. But, t h i s e r r o r i s not going t o be l a r g e r than t h e , e r r o r i n the i n d i v i d u a l l i n e s ; K a l e r (1976a) has shown t h a t mean f i t t i n g e r r o r s between weak p h o t o g r a p h i c a l l y observed l i n e s and str o n g p h c t o e l e c t r i c a l l y observed l i n e s i s about 5 percent i f no sys t e m a t i c e r r o r s are 68 present. T h e r e f o r e , t h i s type of e r r o r must become an important f a c t o r o n l y when s c a l i n g the f a i n t e s t l i n e s , and the o b s e r v a t i o n a l e r r o r r e l a t e d t o the l i n e ( s ) being used f o r determining the s c a l e f a c t o r was def i n e d as i n d i c a t i v e o i the u n c e r t a i n t y i n t r o d u c e d by the s c a l i n g process. The f i n a l r e l a t i v e i n t e n s i t i e s (column <I>, Table VI) and i t s u n c e r t a i n t i e s were c a l c u l a t e d as a weighted mean; the weighting f a c t o r s being the u n c e r t a i n t i e s i n the b a s i c l i n e -r a t i o s . The e v a l u a t i o n of systematic e r r o r s as a f u n c t i o n of wavelength, i n t e n s i t y , and instrument used was done by: i) p l o t t i n g the f i n a l e r r o r (column E r r o r , Table VI) as a f u n c t i o n of wavelength (Figure H ) , i i ) comparing our r e s u l t s with K a l e r ' s o b s e r v a t i o n s ( F i g u r e s 5, 6, 7, and 8) and, i i i ) comparing our r e s u l t s with t h e o r e t i c a l c o n s i d e r a t i o n s (Figures 9 and 10). 69 F i g u r e 4 O b s e r v a t i o n a l e r r o r vs wavelength • • • • o o ° ° oo a ° o o o 0 o • • 0 o ° o <© a ° ° • o 0 • "io XIAIXIO3 ° : L i n e s with more than one measurement n : L i n e s with only one measurement Ik : K a l e r Iw : Wynne Camera Ik : K a l e r Iw : Wynne Camera ° : MKNO A : KPNO 74 Fig u r e 9 NGC 7027: Paschen Decrement O I I I I I I I I I I I I I I I I I I I I 6 8 10 12. U 16 16 20 : Observed I n t e n s i t y : Quantum number o f the r e s p e c t i v e t r a n s i t i o n . : Theo. Te 10«K, Ne 10»cm-3 : Theo. Te 10*K, Ne 10*cm-3 : T h i s work, • : Ka l e r e t a l . (1976) 75 l i ^ u r e JO NGC 7027 ; H e l l Pfund Decrement o J I I I I I I I I I I I I I I I I I 6 8 10 12 U 16 18 20 h Observed I n t e n s i t y Quantum number of the r e s p e c t i v e . t r a n s i t i o n . Theo., Te 10*K, Ne 10 6cm~3 Theo. Te 10*K, Ne 10*cm~3 T h i s work, A : K a l e r et a l . (1976) 76 The r e s u l t s presented i n F i g u r e 4 agree q u i t e well with the c o n c l u s i o n s reached while a n a l y s i n g the DAO September 1977 data only (Table VII and F i g u r e 3). The important p o i n t to emphasize i s t h a t there i s no i n d i c a t i o n of obvious c o r r e l a t i o n between e r r o r s i n the data and wavelength. Frcm F i g u r e s 5, 6, 7, and 8 we i n f e r t h a t : i ) There i s no s y s t e m a t i c wavelength e f f e c t over the range i n 3 x 10 _ 2<I<1 g r e a t e r than about 10 percent.. i i ) For I<3 x 1 0 ~ 2 I ( H c < ) the s c a t t e r of p o i n t s i n c r e a s e s as we c o n s i d e r f a i n t e r , l i n e s , but there i s no s i g n of s y s t e m a t i c e f f e c t with the e x c e p t i o n cf F i g u r e 7, which shews our r e s u l t s s y s t e m a t i c a l l y l a r g e r than K a l e r ' s . , But, because o f the l a r g e u n c e r t a i n t i e s of these measurements, we are not i n a p o s i t i o n t o decide i f t h i s s y s t e m a t i c e f f e c t i s r e a l or not (see F i g u r e 9 and 10) . i i i ) In the range of i n t e n s i t i e s from 3.0 x 1 0 - 3 to 2.0 x 1 0 - 2 the Schmidt camera r e s u l t s from MKO and e s p e c i a l l y KFNO seem to be underestimated by a f a c t o r of about 15 percent.. F i g u r e 9 presents a comparison of the t h e o r e t i c a l Paschen decrement with K a l e r ' s and ours,. The agreement between our data and theory i s q u i t e good, c o n f i r m i n g the l a c k of any obvious systematic e r r o r . However, f o r n>16 ( 8503A) the 77 spectrum s t a r t s g e t t i n g very crowded and the l i n e s i n c r e a s i n g l y f a i n t with the r e s u l t t h a t r o t h o b s e r v a t i o n a l decrements are underestimated. F i g u r e 10 presents an e g u i v a l e n t comparison, but f o r the H e l l Pfund decrement.. The H e l l l i n e s a r e , i n g e n e r a l , f a i n t l i n e s and t h i s f a c t i s shown by the l a r g e r s c a t t e r c f p o i n t s , but a s i m i l a r c o n c l u s i o n to the one i n the p r evious f i g u r e can be reached: i n t i e range o f wavelength between 5700 and 10000A our data presents no obvious i n d i c a t i o n s of systematic e r r o r n e i t h e r as a f u n c t i o n of wavelength nor i n t e n s i t y , except f o r the higher n v a l u e s . . T h i s p o i n t w i l l be d i s c u s s e d i n more d e t a i l i n Chapter I I I , when the p h y s i c a l c o n d i t i o n s i n the nebula w i l l be d e r i v e d . The l a s t t e s t a p p l i e d to our data was based on the f a c t t h a t the s p e c t r a of nebulae c o n t a i n s e v e r a l p a i r s of l i n e s t h a t represent t r a n s i t i o n s from a common upper l e v e l . , These l i n e r a t i o s can be p r e d i c t e d from the t r a n s i t i o n p r o b a b i l i t i e s and do not depend on p h y s i c a l c o n d i t i o n s . . Table IX g i v e s the t h e o r e t i c a l r a t i o , E , f o r a l l o f those doublets present i n our data. L i n e - r a t i o s have been c o r r e c t e d f o r i n t e r s t e l l a r e x t i n c t i o n p r i o r to t h i s t e s t . F i n a l l y , i t should be pointed out t h a t t h i s t e s t depends on the i n t e n s i t i e s of the l i n e s . . . G e n e r a l l y speaking, these p a i r s are b r i g h t l i n e s with only an i n t e n s i t y range of about a 78 f a c t o r of t h r e e f o r cne r a t i o and, t h e r e f o r e , cannot be considered as an i n d i c a t o r of the e r r o r s attached to r a t i o s between very f a i n t and strong l i n e s . Table IX shows t h a t the departure from the expected value i s l e s s than 11 percent f o r a l l of these r a t i o s with the exception cf the r a t i o i.01j] 6300, 6363, But t h i s r a t i o i s the l e a s t r e l i a b l e of a l l of them because of a i r g l o w contamination. Therefore, cur previous statement of no syst e m a t i c e r r o r s as a f u n c t i o n of wavelength and an o v e r a l l o b s e r v a t i o n a l e r r o r l e s s than 11 percent f o r the s t r o n g e s t l i n e s i s again confirmed. 79 Tabl e IX T h e o r e t i c a l and observed l i n e r a t i o s I T T 1 T 1 I I I I I i |Element jWavelength j Btheo j Robs | IRtheo-Rohsl/Rtieo| I I I I I I I L S I I i g J9532-9069 | 2.43 | 2.37 | 2.49E -2 I I I I I I I I UCLIVj] 18045-7530 | 2.34 j 2.07 | 1. 13E -1 I I I i l l I I t O l I g 17319-7330 | 1.24 | 1.21 | 2.28 -2 | I I I I I I ItARIIIi] |7135-7751 | 4.19 j 4.25 | 1.45-2 | I I I I I I | J . ARVjj 17005-6435 | 2.13 \ 1.94 | 8,63 -2 J I I I I I I l i M I i g I6584-6548 | 2.95 | 2.89 | 1.92-2 | I I I I I I Ii 01(3 16300-6364 | 3.14 | 3.65 | 1.62 -1 | I I I I I I L r J 1 , L ; L 1 80 2.5 MONOCHROMATIC TWO-DIMENSIONAL OBSERVATIONS D i r e c t photographs of s e v e r a l p l a n e t a r y nebulae and HII Regions were taken i n the l i g h t of s e v e r a l emission l i n e s u s i ng both the UBC area photometer (50 x 50 diode . array) and the JPL-CCD camera (400 x 400 p i x e l a r r a y ) . The former was used d u r i n g two n i g h t s i n September 1975 mounted at the Casse g r a i n focus (f/18) of the 1,8m t e l e s c o p e a t the.DAO, while the l a t t e r was used f o r f o u r n i g h t s i n January 1978 mounted at the Cassegrain focus (f/7.5) of the 1,5m t e l e s c o p e at CTIO. The o r i e n t a t i o n and angular s c a l e of the systems were determined by using a s u i t a b l e v i s u a l double s t a r (DAO) and from the o b s e r v a t i o n s of Ori o n A (Trapezium) and the p l a n e t Saturn a t CTIO. T h i s l e d to " s c a l e s i z e s " of .62 a r c s e c d i o d e - 1 at DAO and .41 a r c s e c p i x e l - 1 a t CTIO, which correspond to a square f i e l d of about 30 a r c s e c (DAC) and 2.8 arcmin (CTIO) area on the sky. . Guiding was done on the b r i g h t e s t spot of the nebula (DAO) and on o f f - s e t s t a r s a t CTIO. The i n t e r f e r e n c e f i l t e r s used are summarized i n Table X. We should p o i n t out t h a t because of the r a t h e r wide band-pass 81 of the f i l t e r s used with the B e t i c o n a r r a y , the E AO o b s e r v a t i o n s are not e x a c t l y monochromatic. S p e c i f i c a l l y , the Hc( f i l t e r has £NII] 6584, 6548A contamination and the LSXIQ f i l t e r has Hel 6678A and H e l l 6683A contamination. Objects were centered by a s h o r t exposure taken immediately before the main exposure. The data obtained and p e r t i n e n t i n f o r m a t i o n i s presented i n Table XI. . Table X I n t e r f e r e n c e f i l t e r s E AO CTIO r T — ~ 1 1 HI 4862 | 12.5| HI 6564 | 5- 11 £ N i l J 6584 | 5.1| I S I I I J 9532 | 20.0| Hel 10830 | 20.0| Table XI Gaseous nebulae observed P l a n e t a r y Nebulae | Object | Obs | F i l t e r F |NGC 1535 • i CTIO -+ I He* I |IC 418 | CTIO I Hp |IC 418 CTIO I Ho( |IC 418 CTIO I [ N i l ] |IC 418 CTIO I [ S I I I ] |IC 418 CTIO I | Hel I | NGC 2440, CTIO I Hp |NGC 2440 CTIO I . H« |NGC 2440, CTIO I I N i l ] - l |NGC 2440| CTIO I [ s i i i o I JNGC 3132 CTIO I Hp |NGC 3132 CTIO I H< |NGC 3132 CTIO I [ N i l ] |NGC 3132 CTIO I [ S I I I ] Exposure (sec) 8 4 4 6 0- 30 20- 10 240-150 180- 90 240 360-180 120- 60 360-180 600-180 360 180-180 600-600 300-300 Hour Angle * 0:40w 0: 0 Q: 0: 0; 1 0 1; 1; 20e-0: 35e-0: 10e-0j 00e-0: 19w 24w 21w 29w 36w 06w-0. 46w-0 28w-0 47w-1: 50w 43w 59w 03w — - + 1: 1: 1: 2: 14e-0: 36e-1: 53w-2: 06w-2: 50w 35w 14w 26w Frame 4 -i I 200x200| I 1 200x200| 200x200| 200x200| 200x200| 200x200| j I 200x200 I 200x200j I 200x2001 I 200x200 I i 200x200| 200x200j 200x200| 200x2001 T a b l e XI(cont.) i ; — ' . — ~ i — • I I |NGC 3242|CTI0 I I |NGC 3242|CTIO I I |NGC 3242|CTIO I 1 |NGC 3242|CTIO I I i I |NGC 7027|DAO 1 1 |NGC 7027JDAO I I |NGC 7027|DAO I I \- 1-I 7662|DAO I 7662|DAO I I NGC I |NGC I i Kfi 1 15 0-240 I o :05e- 1 :01e| 200x200 Ho< 1 150- 120 I 1 : 11e| 200x200 t N i l 3 | 600- 240 i o :20w-0 :49e | 200x200 I s i n 3 | 300- 240 i o :26w-0 :44e| 200x200 — 4 — I — - + — — + [ O I I I j [ S I I J {.oin 3 1800 1800 1800 1800 1800 1: 12w 0:30w 6: 27w 3:07w 3:54w 50x50 50x50 50x50 1 50x50 50x50 * = Hour Angle at the beginning of the exposure (CTIO) * = Hour Angle at the end of the exposure (DAO) T a b l e XI(cont.) HII Eegions Object Obs F i l t e r r + 4 | (.. — 1-I NGC 1976 | C T I O | | 120-60 | 0:55w-2: 05w| I NGC 1976|C T I O | H * | 6 0- 30 | 0:44w-2: 01 w| | NGC 1976 | C T I O | [ N I I J | 900- 60 | 1:23w-2: 09w| | NGC 1976|CTIO | [ S I I I J | 120-60 | 1:30w-2: 11 w | | NGC 1976|CTIO | Hel | 600-300 j 1:56w-2: 19w| | NGC I |_ 3372|CTIO | H p | - _ - . — — — [600 (.-0:11e |NGC 3372|CTIO | H*! | 240 ! 0:38e | NGC 3372|CTIO | [ N i l j] 900 ! 0 :06w | NGC 3372|CTIO | tSI I I i ] 1600 I 0:42w I |NGC 3372JCTIO | H p ' 36 0-300 | 0:53e- 1: 16e| |NGC 3372|CTIO | Hc< I 6 0-120 | 1:08e- 1: 2Se| | NGC 3372JCTIO | t N i l >] 480- 300 | 0:35e- 1: 02e| | NGC 3372|CTIO | i SII I f] | 300 I 0:22e i L i . J L. Exposure (sec) Hour Angle * Frame 400x400| 400x4001 400x400| 400x400| 400x400| j 400x400, 400x400| 400x400| 400x4001 400x4001 400x400 400x400j 400x400 * = Hour Angle at the beginning of the exposure 86 an o b s e r v a t i o n i n each f i l t e r c o n s i s t e d c f : i ) an o b j e c t frame, i i ) a dark frame of the same exposure as the o b j e c t frame ( s u b t r a c t i o n of dark c u r r e n t ) , and i i i ) a frame of a unif o r m l y i l l u m i n a t e d f l a t f i e l d (dawn sky) t o c a l i b r a t e v a r i a t i o n s i n s e n s i t i v i t y a c r o s s the f a c e of the d e t e c t o r . . At DAO, a f t e r each of these steps s e v e r a l short dark exposures (il minute) were taken with the purpose of s u b t r a c t i n g r e s i d u a l f i x e d p a t t e r n s . . (Mochnacki, 1977) 87 2. 6 EAT A REDUCTIONS The r e d u c t i o n of the data f o l l o w e d standard procedures of area photometry t h a t have been d e s c r i b e d i n d e t a i l by Crane (1S75). B r i e f l y , the o b j e c t frame was reduced by s u b t r a c t i n g the dark frame and d i v i d i n g the r e s u l t by the f l a t f i e l d exposure. For the R e t i c o n a r r a y data, where r e s i d u a l f i x e d p a t t e r n e f e c t s were observed, the 1 minute dark exposures were s u b t r a c t e d from the o b j e c t , sky, and f l a t f i e l d exposures before the above r e d u c t i o n was done. . The sky c o n t r i b u t i o n was determined from r e g i o n s o f the p i c t u r e uncontaminated by the objeer (or s t a r s ) . A c o n s t a n t sky b r i g h t n e s s of t h i s l e v e l was s u b t r a c t e d from each image. In the case of the H^, H*, and j . N i l 3 f i l t e r s t h i s c o n t r i b u t i o n was n e g l i g i b l e , due to the narrow band pass o f these f i l t e r s . , T h e r e f o r e , the g e n e r a l p r o c e d u r e f o r the r e d u c t i o n of the two-dimensional data i s as f o l l o w s : f o r the i j - t h element, 88 where i s the reduced i n t e n s i t y , E -l2 i s the raw measurement, D l 3 i s the dark c u r r e n t measurement f o r the same i n t e g r a t i o n time, F l 3 i s the f l a t f i e l d measurement, and <s> i s the sky background. The f l a t f i e l d c o n t r i b u t i o n has been p r e v i o u s l y normalized, < 3 a ^ ( 1 5 ) where IL i s the observed i n t e n s i t y with the proper dark c u r r e n t s u b t r a c t e d , . For the E e t i c o n d a t a , Formula 1 4 should take the form: -f. - ^ L 3 -1>13 - 1 ^ 3 (16) where r e p r e s e n t s the r e s i d u a l f i x e d - p a t t e r n t h a t was present i n t h i s data. The f l a t f i e l d c o r r e c t i o n r e q u i r e s f u r t h e r e x p l a n a t i o n . S o l i d - s t a t e d e t e c t o r s , when used f o r monochromatic o b s e r v a t i o n s , show strong i n t e r f e r e n c e p a t t e r n s due to the 89 t h i c k n e s s f l u c t u a t i o n s i n the a r r a y , coupled with the in c r e a s e d transparency of s i l i c o n i n the n e a r - i n f r a r e d . In our o b s e r v a t i o n s , the s i t u a t i o n i s as f o l l o w s : i) The two-dimensional E e t i c c n data does not shew t h i s problem. i i ) In the CCD data, f r i n g i n g i s present f o r wavelengths g r e a t e r than about 6500A, At H«( 6563A, the f r i n g i n g amplitude i s between ten and twenty p e r c e n t , at i S I I I ] 9532A , the amplitude i s g r e a t e r than f i f t y percent,. These f i g u r e s apply t o data without the f l a t f i e l d c o r r e c t i o n . When t h i s c o r r e c t i o n i s a p p l i e d , the f r i n g i n g i s reduced to an amplitude of about ten to twenty percent of the o r i g i n a l cne, The r e f o r e , we were not able t o produce a f l a t f i e l d t h a t would e l i m i n a t e completely t h i s problem. , Dusk or dawn sky, moonlight, the Ori o n Nebula and the i n t e r i o r of the dome il u m i n a t e d by an incandescent lamp (the l a s t t h r e e sources out-of-focus) were used f o r t h i s purpose and a f t e r the f i r s t t r i e s i t was obvious that the most s t a b l e source was the sky. A t y p i c a l n i g h t l y v a r i a t i o n f o r a f l a t f i e l d over the whole array was about three to f o u r percent; but, because we were only u s i n g the "best" part c f the ar r a y , t h i s value should be considered as an upper l i m i t . . 90 We can summarize by saying t h a t at Hot 6563 and £NIIJ 6584 the f r i n g i n g i s a minimum e f f e c t and i t can be t r e a t e d as " n o i s e " because i t i s n o t i c e a b l e only at the image nois e l e v e l . . At «.SIIIi] 9532 and Hel 10830, the f r i n g i n g i s severe and these n e a r - i n f r a r e d exposures show a f r i n g i n g p a t t e r n superimposed on the image. However, i t should be p o i n t e d out t h a t these comments d e s c r i b e the g e n e r a l s i t u a t i o n and e x c e p t i o n s e x i s t . T h i s s i t u a t i o n can be seen by comparing F i g u r e 11, NGC 3132 at [SIIIi] 9532A No F l a t F i e l d C a l i b r a t i o n , with the [ S I I I J image shown i n F i g u r e 22d. I n t h i s case, the f l a t f i e l d c a l i b r a t i o n d i d not reduce the f r i n g i n g amplitude at a l l , while the [ S I I I i ] 9532 images of the p l a n e t a r y nebula NGC 3242 show almost no f r i n g i n g p a t t e r n (Figure 24d)., Thus, the amplitude of these f r i n g e s i s a f u n c t i o n of sky v a r i a t i o n s and t e l e s c o p e p o s i t i o n . A source of uniform i l l u m i n a t i o n i s s t r i c t l y necessary i n the dome i f observers expect t c do s u r f a c e photometry with t h i s type of d e t e c t c r . As we j u s t mentioned, the sky i s not uniform enough, e s p e c i a l l y i n the n e a r - i n f r a r e d where strong airglow emissions are present, and which are a l s o h i g h l y v a r i a b l e through the night. 92 As a f i n a l step i n data r e d u c t i o n , d e f e c t i v e p i x e l s (diodes) were r e p l a c e d with t h e . i n t e r p o l a t e d mean of ad j a c e n t p i x e l s (diodes) and a th r e e by three running mean smoothing r o u t i n e was a p p l i e d to a l l reduced frames. Also, i n order to r a t i o two exposures i t - i s necessary t o r e g i s t e r them by seme means, such as using f i d u c i a l f e a t u r e s ( f i e l d s t a r s ) . In the case o f narrow-band exposures, t h e r e are no f i e l d s t a r s and the s u p e r p o s i t i o n o f c e n t e r s of g r a v i t y and/or the c a l c u l a t i o n of c e n t r o i d s of i s o p h o t a l contours g i v e mean displacements with an accuracy of l o c a t i o n e q u a l or l e s s than cne p o i n t of the a r r a y . . Observations through narrow-band pass f i l t e r s show no sky c o n t r i b u t i o n and t h e r e f o r e the data outside the nebula w i l l c o n s i s t of r a t h e r s m a l l numbers which l e a d t o l a r g e f l u c t u a t i o n s i n the r a t i o . In order t o avoid t h i s type of n o i s e , the r a t i o betwen two images i s s e t to zero whenever the i n t e n s i t y i n e i t h e r image f a l l s below 2-3 standard d e v i a t i o n s above the background l e v e l . , N e v e r t h e l e s s , due to the d i f e r e n c e i n s i z e between the two images, a s p u r i o u s enhancement of the r a t i o s i s observed i n the cute r r e g i o n s of the nebula. T h i s e f f e c t a l s o accounts f o r the sharp edges shown by the r a t i o frames,. 93 2, 7 THE COMTAL VISION ONE IMAGING SYSTEM T h i s imaging system was used f o r p u t t i n g the data i n t o a f i n a l form,. 35 mm s l i d e s o f the images d i s p l a y e d on the screen of t h i s system were obtained and the. photographs presented i n t h i s t h e s i s are r e p r o d u c t i o n s of these s l i d e s . . In g e n e r a l , l i n e f i l e s o f (max) 256 bytes per l i n e and 256 l i n e s are t r a n s f e r r e d t o the Comtal System frcm the main campus computer (the Amdahl 470 V6) v i a a HE21MX minicomputer. As each p i x e l i s represented by numbers between 0 and 255 (8 b i t s ) , the image f i l e s i z e i s 256x256x8 b i t s . . The o r i g i n i s defi n e d to be the l e f t upper corner o f the arr a y . . One f u r t h e r r e s t r i c t i o n i s t h a t no decimal code 13 can be found i n the inp u t data. The d i s p l a y i s i n black and white, f u l l c c l o r , or pseudo-c o l o r . A b u i l t - i n image processor performs a l l hardware p r o c e s s i n g f u n c t i o n s upon r e c e i v i n g orders frcm the keyboard, Areas of i n t e r e s t on the image can be d e f i n e d by a t r a c k - t a l l c u r s o r . D i s p l a y f u n c t i o n s i n c l u d e an i n t e n s i t y s c a l e a t the bottom edge of the array (gray of pseudo-cclcr) and gr a p h i c o v e r l a y s (upper l e f t hand corner o f f i r s t c h a r a c t e r i s p l a c e d at c o o r d i n a t e s p e c i f i e d by t r a c k - b a l l c u r s c r ) , The user , 94 under keyboard commands, i s able to perform simple a r i t h m e t i c o p e r a t i o n s , compute histograms, zccm, m i n i f y , s p i n , or r o l l images.. The a d d i t i o n o f c o l o r to the image r e q u i r e s a change from a s i n g l e memory plane to a three memory plane, C o l o r images are obtained by a s s i g n i n g images 1 , 2, and 3 to the c o l o r s Green, Bed, and Blue.. F u l l - c o l o r d i s p l a y r e q u i r e s three images and as we have 8 b i t s per p i x e l per image, there are 2 2 4 p o s s i b l e c o l o r combinations. ' Pseudo-color r e p r e s e n t a t i o n r e q u i r e s only one image and the system i s set such t h a t t o the 8 b i t s per p i x e l i n the black and white space correspond 2 1 2 b i t s i n c o l o r space. . In other words, the design c h o i c e f o r t h i s mode was 4 b i t s per c o l o r . The exact image-to-color assignment i s obtained by d e f i n i n g s p e c i f i c " f u n c t i o n maps", a r e l a t i o n between b r i g h t n e s s l e v e l s i n the bl a c k and white space and transformed (color) b r i g h t n e s s l e v e l s . . T h i s method i s based on the idea of an a d d i t i v e c o l o r system. When green, red, and blue are combined i n p r o p o r t i o n a t e amounts, they add up t c a c o l o r p erceived as white. The s p e c i f i c p a t t e r n used to rep r e s e n t our data corresponds roughly t o a "heat" map ( b l a c k - r e d -95 orange-white), where black r e p r e s e n t s the minimum value on the data array and white the maximum.. F i g u r e 12 shows these f u n c t i o n s maps with the x-axis r e p r e s e n t i n g the a c t u a l b r i g h t n e s s l e v e l s and the y- a x i s the transformed (color) b r i g h t n e s s l e v e l s . F i g u r e 13 shows the a p p l i c a t i o n of these three f u n c t i o n maps to an image of the p l a n e t Saturn. The l a s t o f the fou r images r e p r e s e n t s the a d d i t i o n of the f i r s t three and shows the type of f a l s e - c o l o u r r e p r e s e n t a t i o n that w i l l be used with our two-dimensional data. The programs t h a t are needed t o t r a n f e r data f i l e s from the Amdahl computer to the HP21Mx are contained i n the software package w r i t t e n f o r the r e d u c t i o n and a n a l y s i s o f the two-dimentional data. T h i s package i s explained i n f u l l d e t a i l i n Appendix I . A complete d i s c u s s i o n of the a p p l i c a t i o n of the Comtal Imaging System to a s t r o n o m i c a l imagery i s fcund i n Concal et a l . (1979). FUNCTION MftP: BLUE Saturn:blue c o l o u r cnly Saturn:green+red+blue 98 I I I . NGC 7027 3.1 EASIC DATA T h i s nebula, of about ten arc sec i n diameter, must be cne of the most f r e q u e n t l y observed p l a n e t a r y nebulae. I t has the highest emission measure among these o b j e c t s , i s a s t r o n g i n f r a - r e d source and a l l observable r a d i a t i o n comes from the nebular l i n e s and continuum with no c o n t r i b u t i o n from the c e n t r a l s t a r , I t i s not a t y p i c a l p l a n e t a r y m o r p h o l o g i c a l l y nor s p e c t r o s c o p i c a l l y , showing an extremely i r r e g u l a r appearence ( T e r z i a n , 1977) and a wide range of i o n i z a t i o n ([OI] to i FeVII]) i n i t s spectrum (Ka l e r , 1976a), O p t i c a l o b s e r v a t i o n s (Kaler et a l . ,1S76a) and r a d i c s y n t h e s i s and recombination l i n e o b s e r v a t i o n s (Mottman,1973) seem to i n d i c a t e a d e n s i t y g r a d i e n t from about 3x10*cm - 3 at the edge of the nebula t c 3x10 5cm - 3 cr g r e a t e r nearer the c e n t e r with a constant e l e c t r o n temperature of about 11500K i n the outer r e g i o n s . However, t h i s p i c t u r e of an inhomogeneous nebula i s not suported by r a d i o continuum o b s e r v a t i o n s ; f o r example, Scott (1973) f i n d s t h a t h i s o b s e r v a t i o n s are c o n s i s t e n t with models of reasonably constant d e n s i t y of the c i d e r of 10*cm - 3 99 and constant temperature of about 13000K. There i s seme evidence of s t r a t i f i c a t i o n i n the nebula: the s e p a r a t i o n of the r a d i a l components of l i n e s decrease with i n c r e a s i n g i o n i z a t i o n p o t e n t i a l (Wilson, 1950). Radio-continuum maps by T e r z i a n (1977) with a r e s o l u t i o n of about 2.5 a r c s e c , have shown t h a t the s t r u c t u r e of t h i s nebula i s much more r e g u l a r and symmetric i n the r a d i o r e g i o n than i n the o p t i c a l one. T h i s i s a l s o t r u e f o r the i n f r a r e d maps ( B e c k l i n , 1973), at a wavelengh of about 10yW, c a l l i n g f o r a uniform mixture of gas and dust. T h e r e f o r e , as suggested by Osterbrock (1974), the apparent o p t i c a l s t r u c t u r e must be due to e x t e r n a l dust. T h i s was shown to be t r u e by H i c k s e t a l . (1976) who showed that the [ O I I I ] 5007A l i n e shows a double peak s t r u c t u r e which corresponds to an expansion v e l o c i t y of about 13.5 kmsec - i and the i n t e n s i t y r a t i o f o r the two components, I ^ e /l-rnoi i s g r e a t e r than one, s u g g e s t i n g an i n t e r n a l e x t i n c t i o n of about 0.34 mag near the o p t i c a l c e n t e r . T h i s nebula i s h e a v i l y reddened (mean t o t a l e x t i n c t i o n of the order of 3.6 mag, Osterbrock, 1974), the e x t i n c t i o n seen towards NGC 70 27 i s thus Cf e x t e r n a l o r i g i n . E x t i n c t i o n cf the order of f i v e to s i x mag has been r e p o r t e d by B o h l i n et j j U (1975) i n the u l t r a v i o l e t p a r t of the spectrum (~ 1500-2400A) . 1 0 0 Molecular hydrogen has been detected by T r e f f e n s e t a l . ( 1 S 7 6 ) . M e r r i l l e t a l . ( 1 9 7 5 ) d e t e c t e d a f e a t u r e at 3 . 3 ^ t h a t has not yet been i d e n t i f i e d . . Dabrowski e t a l . ( 1 9 7 7 ) suggested HeH + as a source f o r t h i s f e a t u r e , but Scrimger et al. . ( 1 9 7 8 ) using a Michelspn i n t e r f e r o m e t e r searched u n s u c c e s s f u l l y f o r another three HeH + l i n e s between 1 . 1 / * and 1.6ju/, i m p l y i n g t h a t the u n i d e n t i f i e d 3, . 3 f e a t u r e i s not due to HeH+. , Bregman ( 1 9 7 8 ) measured the SIV( 10.5y*) and N e l l ( 12-8/*/) at four p o s i t i o n s i n NGC 7 0 2 7 and the AIII ( 9 . 0 ^ , ) l i n e a t one p o s i t i o n . He r e p o r t e d t h a t h i s SIV ob s e r v a t i o n s are c o n s i s t e n t with a gas density of about 5 x 1 0 3 c m - 3 , and with the N e l l emission coming from l o w - i o n i z a t i o n r e g i o n s d i s t r i b u t e d inhomogeneously throughout the nebula. A combination of o p t i c a l and i n f r a r e d data gave abundances r e l a t i v e t o hydrogen f o r S, Ne, and A of 1 . 5 x 1 0 - s , 5,. 3 x 1 0-s, and 7 x 1 0 ~ 6 , r e s p e c t i v e l y . McCarthy e t a l , ( 1 9 7 8 ) presented 1 6 - 3 8 y i v o b s e r v a t i o n s of NGC 7 0 2 7 from the Kuiper Airborne Observatory.. From the absence of a p r e d i c t e d £ CIV J 25.91yw/ l i n e , they deduced an e l e c t r o n d e n s i t y g r e a t e r than 2 . 5 x 1 0*cm - 3 i n the r e g i o n s where t h i s i o n e x i s t s , T h e i r o b s e r v a t i o n s r e q u i r e l a r g e dust ( ~ 2 . 5 x 10-"2Mo) and gas (MM 0) masses, which c o u l d be r e l a t e d with the known molecular cloud 101 surrounding the o p t i c a l nebula. T h e r e f o r e , the c o n s t r u c t i o n c f a t h e o r e t i c a l model able to account even approximately f o r t h i s r i c h and complex spectrum, wide spread c f i o n i z a t i o n s t a g e s , p o s s i b l e d e n s i t y g r a d i e n t s and o p t i c a l appearence , i s very d i f f i c u l t . N e vertheless, s e v e r a l geometries and d e n s i t i e s have been suggested f o r t h i s nebula: e. g. . S c o t t (1973), Hick(1S76), S c h i e l d s (1 978) , and Peguignot (1977 , 1978), S c o t t ' s proposed model i s based on the type proposed by Hrcmcv and Kohoutek (1968) to e x p l a i n the o p t i c a l b r i g h t n e s s d i s t r i b u t i o n s of the majority of the pl a n e t a r y nebulae: a c y l i n d r i c a l s h e l l model with a constant e l e c t r o n temperature and d e n s i t y . Good agreement with the o b s e r v a t i o n s i s obt a i n e d f o r a uniform model with Te = 13000K and Ne = 5.0 x 10-*cm-3 with the a x i s of the c y l i n d r i c a l s h e l l at 3 0 t o the l i n e - o f -s i g b t , where a d i s t a n c e o f 1.8 kpb (O'Dell, 1962) i s assumed. However, Hicks et a l . (1S76) pointed out t h a t S c o t t ' s model was not unigue, and t h a t very few p l a n e t a r i e s have s p e c t r a l l i n e s which would i n d i c a t e a c y l i n d r i c a l c o n f i g u r a t i o n , Hicks et a l . proposed t h a t the nebula i n s t e a d was an o b l a t e spheroid, a form f i r s t suggested f o r p l a n e t a r i e s by C u r t i s (1918) and which would present a b i p o l a r c o n f i g u r a t i o n when viewed from an appropiate angle (agreeing with the ra d i o 102 observations) and would a l s o account f o r the behaviour of the s p e c t r a l l i n e s . , S h i e l d s and Pequignot's models are p h c t o i c n i z a t i o n models, t r y i n g to e x p l a i n the observed e l e c t r o n temperature and the f r a c t i o n a l abundances of most i o n s , „ S h i e l d s presents a model based on a d i s t a n c e of 1.5 kpc and a r a d i u s of 0.05 pc (Cahn, 1971), a d e n s i t y of 6 x 10*cm~3 ( M i l l e r et a l , , 1S72) and a volume f i l l i n g f a c t o r of £ = 0.09 ( A l l e r , 1954). F l u x e s i , frcm the Hummer and M i k a l a s (1970) model atmosphere f o r log g =7.0 are used, adopting a temperature of 166000K f o r the c e n t r a l s t a r . Abundances are based on the s c l a r system values (Cameron, 1 973) . G e n e r a l l y speaking, the model accounts very w e l l f o r the p h y s i c a l c o n d i t i o n s i n most of the nebula, but underestimate the abundances of i o n s i n the H +—*H° t r a n s i t i o n zone ( e s p e c i a l l y 0+). He p o i n t s out t h a t a s i m i l a r problem was found with p h o t o i o n i z a t i o n models of S e y f e r t g a l a x i e s ( S h i e l d s et a l . , 1975), Pequignot t r i e s to improve the i n t e r p r e t a t i o n of the a v a i l a b l e o b s e r v a t i o n s by c o n s t r u c t i n g a twc-component model based on the standard p h o t o i o n i z a t i o n theory p l u s charge t r a n s f e r r e a c t i o n s with hydrogen f o r s e v e r a l i o n s (C+, C + 3 , 103 N + 2 , o + 2 , Ne* 2, S + , and S + 3 ) . T h i s model i n c l u d e s a h i g h e r d e n s i t y c e n t r a l component Ne = 2.5 x 10 scm - 3 and a f i l l i n g f a c t o r of £ = 0.2 which extends from R = 1.9 x 10 l 6cm to E = 2.34 x 10 l 6cm and emits about 55'percent of the H^ f l u x , and a second component of low d e n s i t y with Ne = 6 x 1 0 4 c m - 3 and £ = 1, which ends a t E = 3.2 x 10 l 6cm., The agreement with o b s e r v a t i o n s i s q u i t e good, but with d i s c r e p a n c i e s s t i l l present concerning low i o n i z a t i o n stages of C, N, 0 and S. To summarize what i s p r e s e n t l y known about NGC 7027, l e t us say t h a t : i ) I t i s a w e l l s t u d i e d p l a n e t a r y nebula a t o p t i c a l , i n f r a r e d , and r a d i o r e g i o n s . i i ) M o r p h o l o g i c a l s t u d i e s o f t h i s type of o b j e c t (e.g.. G r e i g , 1971) have c l a s s i f i e d i t as an i r r e g u l a r p l a n e t a r y . . The b e s t o p t i c a l p i c t u r e s are A l l e r et a l . (1968) taken with i the 5m t e l e s c o p e i n + [ N i l ] l i g h t , but no o p t i c a l i s o p h o t e s have been p u b l i s h e d . . The only i s o p h o t e maps found i n the l i t e r a t u r e are those of Coleman (1975) and Hicks e t a l . . (1976) at the wavelengths c f H p and H p , and J.OIII 3 50C7A r e s p e c t i v e l y , with both s e t s o f data obtained using e l e c t r o n o g r a p h i c cameras. i i i ) Badio-continuum maps, at 5 Mhz with a r e s o l u t i o n of 2.5 arcsec , and i n f r a r e d maps at 10f*, with a s i m i l a r r e s o l u t i o n , have shown t h a t the s t r u c t u r e of t h i s nebula i s much mere 104 i r e g u l a r and symmetric i n the r a d i o and i n f r a r e d r e g i o n s than i n the o p t i c a l one.- There appears to be a v a r i a b l e , patchy, e x t i n c t i o n accross the nebula t h a t i s r e s p o n s i b l e f o r i t s apparent o p t i c a l s t r u c t u r e . i v ) The r a d i o c e n t e r as g i v e n by T e r z i a n et a l . (1 974) l i e s a t the edge of a dark l i n e which M i l l e r et a l . (1972) have shown to be due to d u st. I f we assume t h a t the r a d i o c e n t e r l i e s near, or a t , the c e n t r a l s t a r , we c o u l d i n f e r t h a t e x t i n c t i o n by dust e x p l a i n s why we are not able to see t h i s s t a r . A l s o , Harlen et a l . (1979) have found a s t a r - l i k e image very c l o s e to t h i s p o s i t i o n and they concluded that they have detected the c e n t r a l s t a r . There i s good agreement between the p o s i t i o n angles of the major a x i s of the r a d i o source (120 ± 15 ) and the o p t i c a l source (135 C u r t i s , 1918). v) The o p t i c a l spectrum of t h i s nebula has been completely re-examined by K a l e r e t al,. (1976) who gave the most up-to-date s e t of r e l a t i v e l i n e - r a t i o s f o r the s p e c t r a l r e g i o n between 3000A and 8500A. There i s s t i l l a need f o r an e q u i v a l e n t work i n the near i n f r a r e d spectrum (~ 6000 -11C00A). vi) Abundances are not w e l l known because an abundance a n a l y s i s has to take i n t o account d e n s i t y , temperature f l u c t u a t i o n s and the wide range of i o n i z a t i o n present i n t h i s nebula. H i g h - e x c i t a t i o n l i n e s are reasonably w e l l f i t t e d by 105 t h e o r e t i c a l models but l o w - e x c i t a t i o n l i n e s are p r e d i c t e d f a r toe weak.. The presence of dust seems t o enhance these low-e x c i t a t i o n l i n e s ( B a l i c k , 1975) because i t absorbs a s i g n i f i c a n t number of i o n i z i n g photons., The processes t h a t c r e a t e (or destroy) and the composition of t h i s i n t e r n a l dust i s a completely open q u e s t i o n . , v i i ) The d i s t a n c e estimate i s q u i t e u n c e r t a i n . , Cahn et a l . (1S71) have r e p o r t e d a d i s t a n c e o f about 1.5 kpc to 2.0 kpc, assuming an o p t i c a l l y t h i n nebula of low mass. But, Cudworth (1974) has r e p o r t e d a d i s t a n c e of about 0.5 kpc assuming t h a t the nebula i s o p t i c a l l y thick,. T h e r e f o r e , there are s e v e r a l areas where the knowledge of t h i s p e c u l i a r o b j e c t may be improved. I n the f i r s t s e c t i o n of t h i s chapter, we w i l l make use of our monochromatic o b s e r v a t i o n s t o i n v e s t i g a t e i n much more d e t a i l both the d i s t r i b u t i o n of the dust r e s p o n s i b l e f o r the o p t i c a l e x t i n c t i o n and the l o c a t i o n of high and low e x c i t a t i o n r e g i o n s . I n the second p a r t , we w i l l study the p h y s i c a l c o n d i t i o n s (e.g. Te and Ne) and compare our r e l a t i v e l i n e -r a t i o s with the p r e d i c t i o n of the models mentioned above. . 106 3,2 EMISSION STRUCTURE Fi g u r e 14 presents the monochromatic images of NGC 7027 obtained with the 50x50 E e t i c o n a r r a y . The three exposures show a s i m i l a r d i s t r i b u t i o n : a smoothed e l o n g a t i o n toward the south-east p a r t of the nebula (major a x i s ) . The H<< •• [ N i l ] and the [ O I I I ] images appear r a t h e r homogeneous,: with the [ S I I ] r a d i a t i o n showing a more inhomogeneous s t r u c t u r e i n the outer p a r t of the nebula. Otherwise, the general shape of the nebula does not d i f f e r very much from an e l l i p s e , whose major and minor axes are given i n Table XII as a f u n c t i o n of the observed wavelength. T h i s Table a l s o i n c l u d e s the outer contour l e v e l expressed as a percentage of the peak i n t e n s i t y i n the image plus previous dimensions reported i n the l i t e r a t u r e . I t i s important to emphasize the comparison of our [ O I I I ] and Ho< + [ N I I i ] images with the h i g h - g u a l i t y p l a t e i n the Ho< + [ N i l ] l i n e s obtained by Minkowski (1968) with the 5m t e l e s c o p e at Palomar Observatory. F i g u r e 14 shows t h a t the exposure l i n e a r i t y and l a r g e dynamic range.cf our system makes i t p o s s i b l e to o b t a i n the s t r u c t u r e of the f a i n t outer and b r i g h t inner r e g i o n s i n a s i n g l e exposure. In p r a c t i c e , we are a b l e to o b t a i n accurate contour maps over a wider range of i n t e n s i t i e s w i t h i n the image. F i g u r e 15 presents a contour p l o t of the [ O I I I ] image which i l l u s t r a t e s the o r i e n t a t i o n . 107 s c a l e , major, minor a x i s , and the three s l i t p o s i t i o n s : 1 ,2, 3 at which M i l l e r et a l . (1972) observed t h i s nebula. T h e i r A. p o s i t i o n corresponds t o the E-W d i r e c t i o n . 108 F i g u r e J_4 NGC 7 0 2 7 : E AO Sept J 9 7 6 109 Table XII NGC 7027: Dimensions and I n t e n s i t i e s F i l t e r t O I I l p I SII |] Dimensions (arcsec) T h i s work P r e v i o u s 23x20 23x20 17x13 14x8 25x23 Outer Contour l e v e l 0. 03 0.03 0, 12 * = photographic p l a t e ** = E l e c t r o n o g r a p h i c camera Reference Minkow s k i * (1S68) Coleman** (1975) 110 l i g u i e 1_5 NGC 7027 : _ O I I I J Image o Q . O 1 0 . 0 2 0 . 0 3 0 . 0 4 0 . 0 50 .# i r 2 0 . 0 3 0 . 0 X PIXEL NO. 111 3. 3 LINE RATIOS The data obtained f o r t h i s nebula allows us to study the v a r i a t i o n s of the r a t i o s H* /J.OIII§, J.SII,3/H<< , and J.SIIJJ / [ O I I I ] a c r o s s the face of the nebula. In t h i s s e c t i o n we w i l l examine each of these three r a t i o s and determine whatever i n f o r m a t i o n they t e l l us about the nebula,. But, f i r s t of a l l , some comments should be made about the r e d u c t i o n procedure. To determine r a t i o s whose mean values could be compared with the p h o t o e l e c t r i c values already r e p o r t e d i n the l i t e r a t u r e , the [ N i l 3 6584,6548A contamination present i n the Ho< image and the Hel 6678A contamination present i n the [SIIjJ image has to be taken i n t o account. Also, r a t i o s should be c o r r e c t e d f o r v a r i a t i o n s i n the r e l a t i v e response of the System and f o r d i f f e r e n t i a l i atmospheric e x t i n c t i o n , as has a l r e a d y been e x p l a i n e d i n Chapter I I . Our s p e c t r o s c o p i c data (Table VI) shows that i f I(H«) = 1.00, then [ N U ] 1(6584) = 0.299 and 1 (6548) = 0. 103. Therefore, the [ N i l ] contamination i s at most of the order of f o r t y percent i n the part of the nebula s t u d i e d s p e c t r o s c o p i c a l l y (the b r i g h t , c e n t r a l c ondensation). Is t h i s 112 r e l a t i o n s h i p v a l i d f o r the r e s t of the nebula? This i s a d i f f i c u l t question to answer i f we do not have a v a i l a b l e [ KIT jj and Htf images of t h i s o b j e c t . I t was assumed t h a t t h i s r e l a t i o n s h i p was v a l i d f o r the r e s t of the nebula based on the f a c t that we are mainly i n t e r e s t e d i n e x t i n c t i o n v a r i a t i o n s across the nebula and the [ N I I j ] 6584,6548/H«: r a t i o i s p r a c t i c a l l y independent of i n t e r s t e l l a r e x t i n c t i o n . The s i t u a t i o n with the [ S I I ] f i l t e r data i s not so good. The Hel 6678a l i n e i s as strong as'the [ S I I ] 6731A l i n e i n our spectrum. The data presented i n Table XI g i v e s f o r I (H ) = 1.00, [ S I I j ] I ( 6731, 6717) = 6.018 and Hel 6678, H e l l 6684 = 0.012. T h e r e f o r e , the contamination could go as high as s i x t y percent. a l s o , because of the d i f f e r e n c e i n t h e i r e x c i t a t i o n p o t e n t i a l s , the [ S I I i ] and the He l i n e s have c e r t a i n l y been formed i n d i f f e r e n t volumes of the nebula. . The data was not c o r r e c t e d f o r t h i s e f f e c t and the r a t i o s [ S I I i J / H * and [ S I I ] / [ O I I I ] w i l l be d i s c u s s e d ' i n a q u a l i t a t i v e r a t h e r than q u a n t i t a t i v e manner. i ) The Ho< /[OIII § Ratio For d e n s i t y bound planetary nebulae Weedman (1968) showed that the [ O I I I ] and H^ r a d i a t i o n s o r i g i n a t e from the same region of the nebula.. For NGC 7027, t h i s was shown to be t r u e 1 1 3 by Hicks et a l , (1970), who obtained i d e n t i c a l e l e c t r o n o g r a p h s a t these two wavelengths. A l s o , c a l c u l a t i o n s of the i o n i z a t i o n s t r u c t u r e of a high e x c i t a t i o n p l a n e t a r y n e t u l a e (TeJJ ~ 10 SK ) show t h a t the 0+ 2 r e g i o n extends as f a r as the H + and He* r e g i o n s (Osterbrock, 1S74), T h e r e f o r e , there e x i s t good reasons f o r e x p e c t i n g that the [ O I I I ] and HI r a d i a t i o n s of NGC 7027 occupy a common e m i t t i n g r e g i o n . C o n s i d e r i n g t h a t the [ O I I I ] 5007,4959A/ H p 4£61A r a t i o i s p r a c t i c a l l y independent of i n t e r s t e l l a r e x t i n c t i o n , we could c o n s t r u c t a map showing the o b s c u r a t i o n caused by the dust by using i n equation (11) the r a t i o H o(/iOIII | 3 i n s t e a d of the H o c / H p r a t i o . . The importance of an o b s c u r a t i o n map f c r NGC 7027 comes frcm the o b s e r v a t i o n s of M i l l e r et a l . (1 972), who presented o b s e r v a t i o n s of the r e l a t i v e i n t e n s i t i e s of the lower Balmer l i n e s at t h r e e d i f f e r e n t p o s i t i o n s i n t h i s nebula. T h e i r main c o n c l u s i o n was t h a t t h e r e was no s i q n i f i c a n t d e v i a t i o n between the recombination theory and o b s e r v a t i o n s of the r e l a t i v e i n t e n s i t y of the Balmer l i n e s . rBut, as a by-product, they presented evidences f o r v a r i a t i o n s i n e x t i n c t i o n over the face of the nebula. The comparison of r a d i o and i n f r a r e d maps with the o p t i c a l nebula prompted B e c k l i n (1973) to s t a t e ; " t h e r e seems t o be a t h i c k cloud of obscuring dust i n f r o n t of the 114 south-west corner of the nebula and v a r i a b l e , patchy, e x t i n c t i o n i n f r o n t of the r e s t o f the s o u r c e " . T h e r e f o r e , i n view of the e x i s t i n g evidence about the presence of dust a s s o c i a t e d with t h i s nebula and the u n c e r t a i n t y i n i t s l o c a t i o n , a map showing the o b s c u r a t i o n caused by the dust was produced by means of eguation (11). As the [ O I I I ] image r e p l a c e d the H image i n these c a l c u l a t i o n s , a f a c t o r equal to the r a t i o [0111] 5007, 4959/Hp 4861 had t o be used t o s c a l e our c o l o r excess E(H« - [OIII]) to E(Ho< - Hp). . The r e s u l t i n g o b s c u r a t i o n map i s presented i n F i g u r e 16a. The dark c o l o u r r e p r e s e n t s areas with the minimum e x t i n c t i o n , while the white areas are the ones where the e x t i n c t i o n reaches i t s maximum., Table XIII compares our averages v a l u e s and M i l l e r ' s (1972), together with values f o r the e x t i n c t i o n c o n s t a n t , c, the c o l o r excess E(B - V), and t o t a l e x t i n c t i o n s at Hp 4861 and a t the c e n t r a l wavelength of the V f i l t e r , d e r i v e d u s i n g the f o r m u l a t i o n presented i n Chapter I . The agreement between our r e s u l t s and M i l l e r et a l . (1972) i s good, with the e x c e p t i o n of p o s i t i o n 3, which i s a f a i n t e r outer r e g i o n . 115 Although i s i s important t o f i n d t h a t o b s e r v a t i o n s obtained with a new type o f d e t e c t o r ( s i l i c o n diode arrays) give comparable r e s u l t s to the ones obtained using more c o n v e n t i o n a l d e t e c t o r s , i t should be emphasized t h a t the main importance o f our o b s e r v a t i o n s r e s i d e s i n t h e i r two-dimensional c a p a b i l i t y , the p o s s i b i l i t y of determining v a r i a t i o n s across the face o f the nebula f o r a l l of these g u a n t i t i e s . Kaler et a l . _ . (1976) have presented values f o r the e x t i n c t i o n c o n s t a n t , c, t h a t vary from c (H«/Hp) = 1.24±0.02 t o c ( r a d i o / H p , Te = 11500K) = 1.50±0.02 with an unweighted mean f o r the o p t i c a l d e termination of c of 1.37±0,02. The value of c(Hc(/Hp) i s s i g n i f i c a n t l y lower than the . irean of the other o p t i c a l l i n e s , but our <c> does net support t h i s low value f o r c; on the c o n t r a r y , i t agrees q u i t e w e l l with the mean value of 1.37±0.02. Also , the value f o r the " r a d i o " c i s 1,46±0.02 when an e l e c t r o n temperature, Te, of 13500K i s adopted. T h e r e f o r e , i t seems t h a t when adopting a h i g h e r value f o r Te ( t h i s s u b j e c t w i l l be d i s c u s s e d i n the next s e c t i o n ) and v a r i a t i o n s i n e x t i n c t i o n are taken i n t o account, the discrepancy between "the o p t i c a l " and "the r a d i o " e x t i n c t i o n c o e f f i c i e n t s i s reduced s u b s t a n t i a l l y . . 116 Table X I I I NGC 7027: E x t i n c t i o n values P o s i t i o n * ** E (Hrf-Hp.) * ** E(B-V) * A (Hp) * c * I Av I I * 3.23 | 1.29| 2.80 2.75 | 1.10J 2.35 3.50 I 1.40| 3.00 4.54 | 1.82| 3.90 3.51 | 1.40| 3.01 A 1 2 3 < > 7. 86 7. 15 6. 82 6. 81 8.56 7.77 12. 39 6. 60 8. 91 1.08 1.02 0.95 0.96 1.18 1.09 1.52 0.91 1.18 0.93 6. 7 9 1.01 1.31 1.01 * = T h i s work ** = M i l l e r e t al^.. (1972) 117 I t i s very i n t e r e s t i n g to note the good correspondance between f e a t u r e s i n the o p t i c a l image (e.g. A l l e r e t a l . (1968) or F i g u r e 15) and the c o l o r excess E (Hc< OIII jj) shown i n F i g u r e 16a. The e x t i n c t i o n i s a minimum at the b r i g h t e s t o p t i c a l f e a t u r e and we can see the o p t i c a l s t r u c t u r e by f o l l o w i n g l e v e l s of i n c r e a s i n g e x t i n c t i o n towards the c u t e r p a r t of the nebula. The " f u z z y " s t r u c t u r e of the outer p a r t s of the o p t i c a l nebula i s due t o the presence of obscuring m a t e r i a l surrounding i t . We a l s o n o t i c e t h a t our data r e v e a l s a s p h e r i c a l nebula with a r a d i u s of 12 arc sec. . The geometric center cf t h i s sphere i s s i t u a t e d at about 2.5 arc sec e a s t and 1,5 a r c sec south of the o p t i c a l nebula ( b r i g h t north-west l o b e ) . . On the other hand, Cudworth et a l ^ . (1 978) have given c o o r d i n a t e s f o r the r a d i o center of t h i s nebula which are s i t u a t e d at about 1.5 a r c sec east and 1.0 arc sec south of the o p t i c a l nebula. T h i s r a d i o c e n t e r c o i n c i d e s (<1 arcsec) with the p o s i t i o n of the s t e l l a r f e a t u r e r e p o r t e d by Harlen et a l . (1S79) . T h e r e f o r e , three independent i n v e s t i g a t i o n s i n d i c a t e t h a t the p o s i t i o n of the unseen c e n t r a l s t a r i s i n a r e g i o n of the nebula t h a t shows heavy e x t i n c t i o n i n our o b s c u r a t i o n map. Thus , e x t i n c t i o n by dust e x p l a i n s why nc c e n t r a l s t a r has been observed. , 118 The r a t h e r l a r g e i n c r e a s e i n e x t i n c t i o n t h a t we d e t e c t toward the outer p a r t of the nebula i s a very important o b s e r v a t i o n a l r e s u l t , because i t i s f u r t h e r evidence t h a t a p p r e c i a b l e amounts of matter e x i s t o u t s i d e the v i s i b l e nebula, and i t i s i n agreement with the l a r g e volume f o r the carbon monoxide emission r e p o r t e d by Mufson et a l , (1975). McCarthy et a l . (1978) showed t h a t t h e i r i n f r a r e d data i s c o n s i s t e n t with a 1 / x 2 o p a c i t y dependence. As carbon has been shown to be over-abundant i n NGC 7027 ( S h i e l d s , 1S78), MacCarthy et a l . (1978) suggested t h a t g r a p h i t e i s probably the dust m a t e r i a l . The problem i s t h a t s e v e r a l forms of s c l i d carbon, e.g. small s p h e r i c a l g r a i n s (r<0. 2ji) up to l a r g e ones (r~1j^), are able t o show the 1/,\z o p a c i t y dependence. Thus, our o b s e r v a t i o n s support the e x i s t e n c e of the s m a l l - g r a i n component because the e x t i n c t i o n due t o l a r g e p a r t i c l e s would be almost n e u t r a l . Matter around p l a n e t a r y nebulae must reduce the amount of i o n i z i n g r a d i a t i o n t h a t reaches the i n t e r s t e l l a r medium from an o p t i c a l l y t h i n nebulae. Hence, Mufscn e t a l . ( 1975) suggested t h a t p l a n e t a r i e s were net as important as sources of heat f o r the i n t e r s t e l l a r medium as f i r s t suggested by T e r z i a n (1S74). However, we should p o i n t out t h a t apart from NGC 7027 only two more p l a n e t a r i e s (NGC 6543 and IC 418) present 119 evidence of molecular c l o u d s a s s o c i a t e d with them. Since these t h r e e p l a n e t a r i e s are o p t i c a l l y t h i c k o b j e c t s (Cudwcrth, 1974), i t might be p o s s i b l e t h a t t h i s expanding s h e l l of molecules, gas, and dust, being a remnant o f the f i r s t e j e c t i o n of matter frcm the c e n t r a l s t a r , i s e a s i l y d etected i n the i n i t i a l o p t i c a l l y t h i c k stage of the l i f e of the nebula (Seaton, 1966). Thus, o p t i c a l l y t h i n p l a n e t a r y nebulae may s t i l l be an important source of heat f o r t i e i n t e r s t e l l a r medium. F i g u r e 16 NGC 7027: Line E a t i o s 120 121 i i ) T h e [SII|/Ho( and f S U 3/1 OIII jj R a t i o s F i g u r e 16b,c presents thesejtwo r a t i o s and, as mentioned p r e v i o u s l y , they w i l l he only I discussed q u a l i t a t i v e l y . . The [ S I I 3 /Ho; r a t i o i s p r a c t i c a l l y independent of i n t e r s t e l l a r e x t i n c t i o n , while the r a t i o J. S I I 3 / [ O I I I 3 i s not. . T h i s d i f f e r e n c e accounts f o r the almost complete f l a t n e s s of the f i r s t r a t i o , while the second one shows a g e n e r a l i n c r e a s e outward. Also, the only ccmmcn f e a t u r e i n these two r a t i o s i s t h e i r enhancement i n the d i r e c t i o n of p o s i t i o n angle 230 -260 (West-South d i r e c t i o n ) . T h i s p o s i t i o n c o i n c i d e s with a very sharp edge i n Minkowsky's 5m t e l e s c o p e photograph and a pronounced compression of the contour i s o p h o t e i n our data (Figure 15). The [ S I I J l i n e s are l o w - i c n i z a t i o n t r a n s i t i o n l i n e s . . T h erefore t h e i r comparison with the h i g h - i o n i z a t i o n l i n e s , e.g. [ O I I I ] 5008, 49596,, should y i e l d s t r u c t u r a l d i f f e r e n c e s i n the nebula.. [ S l i p emission r e p r e s e n t i n supernova remnants c o o l r e g i o n s l o c a t e d behind the expanding shock f r o n t . As pla n e t a r y nebulae are a l s o expanding s h e l l s , we co u l d i n f e r the p o s i t i o n of expanding f r o n t s i n the nebula by the p o s i t i o n of maximum value of r a t i o s l i k e the ones discussed i n t h i s s e c t i o n . 1 2 2 T h e r e f o r e , i f t h i s enhancement i n both r a t i o s i s due to [ S I I ] emission ccming frcm the outer part c f the o p t i c a l nebula, then t h i s i s an i n d i c a t i o n t h a t i n t h i s d i r e c t i o n we are able t o detect the t r a n s i t i o n zone between the HII Region and the HI Region surrounding i t . . 1 2 3 3 - 3 COMPARISON OF SPECTROSCOPIC OBSERVATIONS WITH THEORY i ) I n s t e r s t e l l a r e x t i n c t i o n The f i r s t step i n the comparison of s p ectrophotometric data with t h e o r e t i c a l p r e d i c t i o n s i s the c c r r e c t i o n of the former f o r i n t e r s t e l l a r e x t i n c t i o n - . As we have e x p l a i n e d before, the r e a l r e l a t i v e l i n e i n t e n s i t i e s are determined from the r e l a t i o n s h i p : P o 5 i 0 = Pe^l + C J U ( 1 7 ) where I(^) and I o(>0 are the observed and true r e l a t i v e l i n e i n t e n s i t i e s . We have s e l e c t e d K a l e r ' s ( 1 9 7 6 ) f u n c t i o n , f (>i) # and normalized i t such t h a t f (<*>) = - 1 and f ( H o < ) = 0 . The e x t i n c t i o n constant was taken to be c = 1 , 3 7 ± . 0 2 (Kaler's unweighted mean)., T h i s was done based on the f a c t that t h i s value was o b tained as a mean over 11 d i f f e r e n t r a t i o s and t h a t our <c> i s only 3 % o f f . Such a v a r i a t i o n i s i n s u f f i c i e n t t o s u b s t a n t i a l l y change c o n c l u s i o n s r e g a r d i n g the p h y s i c a l c o n d i t i o n s i n the nebula. , We c o r r e c t e d the r e l a t i v e f i n t e n s i t y r a t i o s given i n Table VI f o r i n t e r s t e l l a r e x t i n c t i o n 124 using formula (17). In what f e l l o w s , i t i s assumed t h a t I means our r e l a t i v e l i n e r a t i o s (Table VI) c o r r e c t e d f o r i n t e r s t e l l a r e x t i n c t i o n . i i ) H I Paschen and H e l l Pfund decrements These two decrements were presented i n f i g u r e s 9 and 10, when the accuracy of the s p e c t r o s c o p i c data was disc u s s e d . The agreement between o b s e r v a t i o n s and theory i s good f o r n < 16, with a l a r g e r s c a t t e r f o r the H e l l Pfund decrement. The av€rage u n c e r t a i n t y i n the observed Paschen l i n e decrement i s of the order of 23 per cent while f o r the H e l l Pfund decrement the average i s 22 per cent f o r n < 15 and ever 60 percent f o r n> 16. We see from F i g u r e s 9 and 10 t h a t the lower p o i n t s of both decrements are i n s e n s i t i v e t o d e n s i t y . The Paschen l i n e s seem to i n d i c a t e t h a t the best f i t occurs f o r Ne ~ 10*cm - 3 while the l a r g e u n c e r t a i n t i e s i n the values of the h i g h e r members of the Pfund l i n e s do not allow us to decide i f the ob s e r v a t i o n s f i t a p a r t i c u l a r decrement. Hcwever, the Pfund l i n e s seem to agree with d e n s i t i e s o f the order of 10 6cm - 3 125 c l o s e t o the center of the o p t i c a l nebula. T h i s value agrees with r e s u l t s presented by Saraph et a l . (1S70) and K a l e r et a l . (1976). 126 i i i ) T h e o r e t i c a l Models f o r NGC 7027 S h i e l d s (1977) and Eequignot (1978) have presented the most up-to-date models s p e c i f i c a l l y a p p l i e d to t h i s nebula. Frcm the comparison of our o b s e r v a t i o n s with t h e i r r e s u l t s , F i g u r e 17, we may i n f e r t h a t : i) Models t h a t i n c l u d e charge t r a n s f e r r e a c t i o n s i n determining the i o n i z a t i o n of heavy elements (Pequignot's model) give a b e t t e r f i t t c the o b s e r v a t i o n s , e s p e c i a l l y f o r i o n s whose i o n i z a t i o n p o t e n t i a l s are of the order of 35 ev (Points 1,2 [ N i l , ] , 3 [ O i l , ] , 4,5 [ S I I I i ] ) . . i i ) h s t a t i c , homogeneous model ( S h i e l d s ' model) underestimates the s t r e n g t h of these l i n e s , while g i v i n g a reasonable f i t to l i n e s produced by i o n s of h i g h e r i o n i z a t i o n p o t e n t i a l . i i i ) Comparison of these models with p r e v i o u s o b s e r v a t i o n s have shown that f o r [NIVp, ±NeV|, [ N i l , ] , [CI,], £ N I ] , [ S I ] , and [ S I I ] l i n e s the disagreement i s l a r g e . Our obs e r v a t i o n s are i n the p o s i t i o n of r a t i f y i n g or d i s p r o v i n g the values of the s t r e n g t h of the [ N i l ] , [ C l i ] , [ S I | , and [ S I I ] l i n e s . Table XIV shows a comparison of our observed r e l a t i v e l i n e r a t i o s with previous o b s e r v a t i o n s (Pequignot (1S78), K a l e r (1976)) and the p r e d i c t e d values by the models f o r these i o n s . 127 For the J. N i l j] 6584, 6548 l i n e s , our value agree q u i t e w e l l with Pequignot's p r e d i c t i o n . Thus, e l i m i n a t i n g the n e c e s s i t y of changing the adopted i n i t i a l values f o r the r a t e c o e f f i c i e n t s f o r the r e a c t i o n s N+2 + H° >N* + H+, N+3 + H° *N+2 + H + and n i t r o g e n a b u n d a n c e i n the model. In the case of the £SII3 l i n e s our o b s e r v a t i o n s agree with the o b s e r v a t i o n s by K a l e r (1976) q u i t e ; w e l l ( d i f f e r e n c e cf about 12 p e r c e n t ) , t h e r e f o r e , s u g g e s t i n g a change i n the models to the assumed charge exchange r a t e and/or the temperature, and d e n s i t y d i s t r i b u t i o n s . For the case of the J.CIJ and [ S I i ] l i n e s , the l a r g e u n c e r t a i n t i e s of our measurements do not permit us to decide i f the d i s c r e p a n c i e s between rthe o b s e r v a t i o n s by Danziger (1S73) and K a l e r (1976) and models are due to tirong assumptions i n the models or e r r o r s i n the o b s e r v a t i o n s . A l s o , the u n c e r t a i n t y i n our value f o r the J.CI3 8727 l i n e i s e q u i v a l e n t ( 8 percent) to the u n c e r t a i n t y i n the value given by Danziger e t a l . (1973), but the values d i f f e r by a f a c t o r of almost 3.. O b v i o u s l y , b e t t e r o b s e r v a t i o n s are r e q u i r e d to s e t t l e t h i s p o i n t . 128 Io : l o b s . I t : Itheo. • : Peguignot A : S h i e l d s "Low C" o : S h i e l d s "High C" Table XIV NGC 7027i l o b s vs Itheo Line | l o b s | S h i e l d s i Pe quignot i * 0 i I N i l 3 L _ 6584| 4.02E 1 4. 7E 1| 1.26E 1 1. 47e 1 4-04E 1 6548| i i I N i l 3 5755| 2.4 E 1 2. OE 1|3.60E-1 4. 60e- 1 i 2. 12E 0 LCI3 9849| 1.4 E-1 4. OE-116.0 E-1 9. 50e-2 1 4.80E-1 i c i 3 9823| 3.8 E-2 I i LCI 3 8727| 3.0 E-1 1, IE- 11 i 9.02E-2 i. si§ 7725| 1- 3 E-1 9. 1E-2| i 6.4 E-2 I s n i] 6725| 1.6 E 0 1. 8E 0| 1..76E 0 2. 2 e 0 1 2.48E 0 * = This work * = High C ** = Others ° = Low C 130 The v a l i d i t y of a model i s a l s o measured by the agreement between observed and p r e d i c t e d v a l u e s f o r Ne and Te. Our o b s e r v a t i o n s permit e l e c t r o n temperature, determinations from the l i n e s of the [ N i l j] and ISIII j] .ions and e l e c t r o n d e n s i t y , determinations from the [ S I I ] i o n . . T h e r e f o r e , i t was p o s s i b l e to determine Te and Ne i n the r e g i o n s of the nebula where N + , S+ + , and S* e x i s t . . Both the Ne and Te c a l c u l a t i o n s were made using the formulae given by Osterbrock (1974) and K a l e r e t a l . (1976). The r e s u l t s are l i s t e d i n Table XT/., The discrepancy observed between our r e s u l t s and the ones by K a l e r et a l . (1976) and Barker (1978a,b) i s due to the d i f f e r a n c e s i n the r e l a t i v e i n t e n s i t i e s o f the l i n e s i n v o l v e d i n the c a l c u l a t i o n of Ne and Te., The agreement i s s a t i s f a c t o r y c o n s i d e r i n g t h a t the r e s u l t s have a f r a c t i o n a l standard d e v i a t i o n of the c r d e r of 25 Table XV NGC 7027J. Te and Ne values Ion I Te (K) | Ne (c m - 3) i * i Nlli] i 15600 12600 16000 | J. SIII,] | 11600 11900 1 | t s i i g i • ' |2.5x10** I | 3.7x10*** 1 |2.8x10**** ) * = i . T h i s work ** = Kaler et a l . (1976) *** = Barker (1978a,b) 132 Table XV presents r e s u l t s t h a t agree with a p i c t u r e of a two zone nebula where Te (I) < Te (II) and Ne (I) > N e ( I I ) . . Zone I being surrounded by Zone I I and Zone I I c o n t a i n i n g ions with i o n i z a t i o n p o t e n t i a l s l e s s than 25 ev. T h e r e f o r e , Te(SIII) (or Te (OIII)) i s a good e s t i m a t o r of the e l e c t r o n temperature f o r Zone I and T (Nil) f o r Zone I I . Obviously, a r e a l p l a n e t a r y i s much more complicated than a s i u p l e two-component model, but an a n a l y s i s i n these terms g i v e a b e t t e r agreement between theory and o b s e r v a t i o n s and a l s o seme i d e a of the e f f e c t of temperature and d e n s i t y f l u c t u a t i o n s . . How do t h e s e r e s u l t s compare with r e s u l t s f o r ether p l a n e t a r y nebulae and models? A l l e r e t a l . (1976) found t h a t Ne (SII) was higher than Ne (Oil) i n about 30 p l a n e t a r i e s . . Barker (1978a) found s i m i l a r r e s u l t s f o r e i g h t cases out of 11. Now, [ S I I ] i s not expected t o be the predominant i o n i z a t i o n stage o f S because of i t s low i o n i z a t i o n p o t e n t i a l (lower than hydrogen),. Thus, [ S I I $ i o n s c o u l d very w e l l e x i s t enly i n r e g i o n s of high d e n s i t y . Boeshaar (1974) showed t h a t [ S I I jj emission came from f i l a m e n t s i n s e v e r a l p l a n e t a r i e s , but Earker (1978a) has questioned the accuracy of Boeshaar's photographic data.. In p r i n c i p l e , our two-dimensional data would be able t o answer t h i s q u e s t i o n , but the Hel 6678A contamination does not allow us to make a d e f i n i t e statement. However, i t should be pointed out t h a t our [SIIiJ image shows a 133 much l e s s homogeneous s t r u c t u r e than the + [ N i l J and £OIII] images and an enhancement r i g h t behind the l i m i t of the HII Eegion ( p o s i t i o n angle 230 t o 260°), coming t h e r e f o r e frcm a higher d e n s i t y r e g i o n . Again, more o b s e r v a t i o n a l work i s needed, e s p e c i a l l y now t h a t astronomers have at t h e i r d i s p o s a l two-dimensional d e t e c t o r s and narrow enough i n t e r f e r e n c e f i l t e r s that permit the mapping of £SIIJ 6717, 6731A s e p a r a t e l y . A map of the r a t i o 6717/6731 would be the most ac c u r a t e way of determining the v a r i a t i o n cf Ne (SII) a c r o s s the f a c e of the nebula. Osterbrock (1974) r e p o r t e d a value of 15300K f o r T e ( O I I I ) . So, our Te (Nil) i s of the c r d e r of Te (OIII) ., Barker (1978a,b) has r e p o r t e d that Te (Nil) i s g r e a t e r than Te(OIII) i n seven o f t h i r t e e n p l a n e t a r i e s b e l i e v e d t o be o p t i c a l l y t h i c k i n the Lyman Continuum, almost egual f o r the other s i x , while being higher i n only one o f s i x of the o p t i c a l l y t h i n o b j e c t s and lower i n the other f o u r . NGC 7027 i s an o p t i c a l l y t h i c k nebula (Cudworth, 1S74), Thus, cur o b s e r v a t i o n s agree with Barker's r e s u l t s . . But t h i s q u e s t i o n i s f a r from s e t t l e d ; f o r example, Dufcur et a l . (1977) presented evidence t h a t the £ OIII i] temperatures sere s y s t e m a t i c a l l y higher than those i n d i c a t e d by £NIIJ i n p l a n e t a r y nebulae belonging to the M a g e l l a n i c Clouds. P r i o r t o our work, a point of c o n t e n t i o n was the c l a i m by 134 Kaler et a l . (1976) t h a t the H e l l Pfund decrement i n d i c a t e d d e n s i t i e s of the order of 10 6 to 10 7cm - 3. Such d e n s i t i e s were incompatible with model p r e d i c t i o n s and o b s e r v a t i o n s ty o t t e r s (e.g. Chaisson et a l . 1976), 4 I t was hoped t h a t our measurements would give a d e f i n i t e answer to t h i s problem. As i t was mentioned i n s e c t i o n 2.4, the l a r g e e r r o r bars i n our H e l l Pfund decrement d i d not allow us to d i s c r i m i n a t e between the d i f f e r e n t t h e o r e t i c a l decrements. . But, the i n s p e c t i o n of our F i g u r e s 9 and 10 c e r t a i n l y f a v o r an e l e c t r o n d e n s i t y i n the range of 10* to 105cm~ 3. Another approach to t h i s problem would be t o c a l c u l a t e the e l e c t r o n d e n s i t y by means the t r a n s a u r o r a l l i n e s cf £0IIijJ 7319,7331A and [ S I I J 4068, 4076A by the method o u t l i n e d by A l l e n (1979). By doing so, and using K a l e r ' s data, we o b t a i n an e l e c t r o n d e n s i t y cf the order of 8 x 10*cm - 3, which being higher than Ne (SII) i s s t i l l no nearer the value r e p o r t e d by Ka l e r et a l . (1976) .. We f e e l t h a t t h i s problem r e g u i r e s o b s e r v a t i o n a l c o n f i r m a t i o n because other r e s e a r c h e r s (e.g. Eeguignot and Chaisson) have not been a b l e t o co n f i r m t h i s high value of Ne. C e r t a i n l y , a s o l i d - s t a t e d e t e c t o r and high r e s o l u t i o n (coude observations) would be the i d e a l s et up f o r ob s e r v a t i o n s of Hydrogen and Helium decrements. 135 IV. NGC 2440, NGC 3132, AND NGC 3242 4, 1 NGC 244 0 T h i s i s a p l a n e t a r y t h a t shows a complicated / patchy s t r u c t u r e over an area with, a r a d i u s of about 10 a r c s e c . An outer envelope with a r a d i u s of about 30 arcsec becomes apparent i n the l o n g e r exposures. From photographs by C u r t i s (1S18) and Minkowski (1964) i t i s concluded t h a t the aost prominent f e a t u r e s are twc c e n t r a l condensations, 7 a r c s e c a p a r t i n a p o s i t i o n angle of 153° and two outer knots at both ends of the major a x i s and about 25 arcsec frcm the c e n t e r of the nebula. K a l e r and A l l e r (1974) have shown t h a t the two outer knots do not l i e on a l i n e with the i n n e r ones and t h a t the b r i g h t , i n n e r envelope i s expanding f a s t e r than t h e . f a i n t outer halo. Wilson (1950) measured a maximum expansion v e l o c i t y of about 30 kmsec - 1 frcm the [NIIi] and J_0II3 l i n e s , No c e n t r a l s t a r i s v i s i b l e . Milne and A l l e r (1974) r e p o r t e d a r a d i u s of 0.1 pc, and an e x t i n c t i o n constant o f c=0.42., A l l e r et a l . (1S 68) r e p o r t e d an e l e c t r o n temperature, T e ( O I I I ) , cf 13500K and an 136 e l e c t r o n d e n s i t y , Ne ( O i l ) , t h a t drops frcm 3x10 3cm~ 3 at the c e n t e r to 1 0 3 c m - 3 o r l e s s along the major a x i s . The spectrum of t h i s nebula has been e x t e n s i v e l y s t u d i e d from the blue r e g i o n up to about 7000A by A l l e r (1957), Kaler and A l l e r (1974), and Boeshaar (1974). The most s t r i k i n g c h a r a c t e r i s t i c of t h i s spectrum i s the change i n the l e v e l of e x c i t a t i o n over a very s m a l l area. L i n e s cf low i o n i z a t i o n p o t e n t i a l , e.g. [ N 2 J and [ N i l ] , are very s t r o n g . A l l e r (1956) presented contour p l o t s i n the l i n e s of [NeVJ 3425, H e l l 4686, H^ 4861, and J.0IIIi3 4959 tra c e d from s l i t l e s s spectrograms secured by Wilson. F i g u r e 18 shows a contour p l o t of our H<* image which i l u s t r a t e s the s c a l e , o r i e n t a t i o n , and p o s i t i o n of a x i s . T h i s s c a l e and o r i e n t a t i o n are v a l i d f o r the r e s t of the data presented i n t h i s chapter (NGC 3132 and NGC 3242). 137 138 F i g u r e s 19 and 20 present the 200x200 images obtained with the CCD camera f o r t h i s nebula. Maximum angular extent i s reached by the emission from the lowest i o n i z a t i o n s t a g e , J.NII3. This i s c o n s i s t e n t with the theory that the general l e v e l of i o n i z a t i o n i n the nebular s h e l l decreases with d i s t a n c e from the c e n t r a l s t a r . The Hp and H* images show s i m i l a r s t r u c t u r e , both images showing fuzzy edges i n a l l d i r e c t i o n s except toward the North-west, where a very sharp edge i s c l e a r l y v i s i b l e , p a r t i c u l a r l y i n the Hp image. F i g u r e 19b i s a magnified (twice) H^ image which shows t h i s e f f e c t more c l e a r l y . As f a r as we are aware s t r u c t u r a l d e t a i l s c f t h i s nature have net been reported b e f o r e . F i g u r e s 20a,b present two exposures of t h i s nebula i n the [ S I I I J l i n e . These images i l u s t r a t e the " f r i n g i n g " problem discu s s e d i n Chapter I I . A short exposure (180 sec) with n o t i c e a b l e f r i n g e s only at l o w - l i g h t l e v e l s and a l o n g e r (600 sec) with strong f r i n g e s superimposed on the image. The s h o r t exposure was magnified twice. In s p i t e of these f r i n g e s , we s t i l l are able to deduce that the [ SIII i ] emission i s concentrated i n the i n n e r s h e l l with very sharp edges. The [SIII,] emission shews the t y p i c a l 139 appearence of a nebula i n a h i g h - e x c i t a t i o n l i n e . F i g u r e 20c, d show the m/H* and £ H I I fl/H* r e s p e c t i v e l y . U n l i k e NGC 7027, t h i s nebula does not shew a c o l o r excess or l e s s constant a c r o s s the face of the i n n e r s h e l l , but showing a sharp i n c r e s e towards the North-West d i r e c t i o n . This r a t i o d e f i n e s very c l e a r l y the l i m i t s of the i n n e r s h e l l . The [NIIjJ/H,,; r a t i o shows an almost constant value over the i n n e r s h e l l with a general i n c r e a s e outward.. In t h i s c a s e , the problem of the " r a t i o - n o i s e " mentioned i n s e c t i o n 2,6 i s very n o t i c e a b l e . The c o o r d i n a t e s f o r the minimum value of t h i s r a t i o d e f i n e the l o c a t i o n of the source of e x c i t a t i o n ( c e n t r a l s t a r ) . T h i s p o s i t i o n has been i n d i c a t e d i n F i g u r e map (Hot/Hp r a t i o ) t h a t i n c r e a s e s s t e a d l y outward. I t i s more 21. 140 l i j u r e 19 NGC 2440j. CTIC January 1978 (a) H, (b) HA rmagnified twice NGC 24401 6534 (C) Ho( (d) [ N i l ] 141 l i a b l e 20 NGC 2440: C1IC January 1978 9532 NGC 2448: 9532 • ^ (a) J. S I I I ] : 180 sec (b) j.SIII]:600 sec (c) Hof/Hp (a) INII3/H« 142 The z e r o - p o i n t f o r these two r a t i o s was determined by means of previous p h o t o e l e c t r i c photometry. Campbell (1968) reported a value of 3.9 f o r the r a t i o [NIIJ/H* i n the i n t e g r a t e d l i g h t of a 31 a r c s e c diaphragm centered at the nebula. K a l e r (1976) rep o r t e d a p h o t o e l e c t r i c measurement of 21.88 f o r the (H* + [ N I I ] ) / H p ratio,. From these two o b s e r v a t i o n s we deduce a value of 4.45 f o r the Balmer decrement. Now, by d e f i n i n g a 30 arcsec diaphragm with i t s o r i g i n at the c e n t e r of the nebula , we o b t a i n the values 1.71 f o r the Balmer r a t i o and 4.83 f o r the «. N i l J/Hof r a t i o . The l a t t e r i s p r a c t i c a l l y independent of any i n s t r u m e n t a l or e x t i n c t i o n c o r r e c t i o n ; t h e r e f o r e , i t i s d i r e c t l y comparable with the p h o t o e l e c t r i c r e s u l t . The agreement, being o f f by about 20 per c e n t , i s a good one c o n s i d e r i n g t h a t Campbell's o b s e r v a t i o n s , having a r e s o l u t i o n of 32 A, were not a b l e to completely i s o l a t e the [ N i l ] from the H<x l i n e . The only ether measurements found i n the l i t e r a t u r e are from Torres-Peimhert et a l . (1977) , who r e p o r t e d a value of 4.2, but i n t h i s case the blend of these l i n e s was more severe and t h i s value was obtained a f t e r deconvolving the H«- p r o f i l e . The comparison of our value f o r the Hoj/H^ with the p h o t o e l e c t r i c one g i v e s us a n o r m a l i z a t i o n f a c t o r cf 0.4. The best estimate t h a t we have f o r the i n s t r u m e n t a l response of the system i s the expected response of the CCD a r r a y (Figure 143 2). From t h i s F i g u r e we f i n d out t h a t the expected response at H p i s about 58 per cent of the one • a t H t f . „ T h e r e f o r e , c o n s i d e r i n g t h a t F i g u r e 2 r e p r e s e n t s a general , expected response of a CCD array and not the response of the whole system , we b e l i e v e t h a t the agreement between observed and expected response i s s a t i s f a c t o r y (about 20% c f f ) - . . We w i l l d i s c u s s t h i s p o i n t a g a i n , when d e a l i n g with the data f o r NGC 3242. We are now i n a p o s i t i o n t o determe g u a n t i t a t i v e l y the changes i n the redenning across the f a c e of the nebula., Table XVI presents s e v e r a l values of the H c x / H ^ r a t i o and s e v e r a l parameters d e r i v e d frcm them i n a s i m i l a r way as i t was done f o r NGC 7027. . The minimum value corresponds to an average over the two b r i g h t i n n e r condensations, the maximum value corresponds to an average taken over the enhacement shown i n the North- West d i r e c t i o n , and the middle value i s an average taken over an area j u s t west of the b r i g t h condensations along the major a x i s . These three areas have been l a b e l e d a,b, and c i n the contour p l o t presented i n Figure 18. . F i n a l l y , F i g u r e 21 i s a diagram combining a l l the i n f o r m a t i o n a v a i l a b l e . We have taken the hydrogen emission as being r e p r e s e n t a t i v e of the i o n i z e d nebula and superimposed the d i f f e r e n t maxima and minima of the others l i n e s and r a t i o s 1 4 4 cn i t . The c e n t e r of the nebula i s d e f i n e d by the minimum of the [NIIJ / H c < r a t i o and shows t h a t the l o c a t i o n of the unseen c e n t r a l s t a r i s j u s t where we would l i k e to have i t : on the major a x i s of the nebula, i n l i n e with the c e n t e r s of the two b r i g h t condensations, and i n an area of i n c r e a s e d e x t i n c t i o n and s i m i l a r t o NGC 7027. . In t h i s same ar e a , the [ S l l l i ] shows an i n c r e a s e with r e s p e c t to and [ N I I J , t e l l i n g us t h a t the i n c r e a s e i n e x t i n c t i o n that we d e t e c t i n t h i s area i s due to the presence of dust.. The £SIIIQ emission has a l a r g e r o p t i c a l p e n e t r a t i o n through dust than : H o ( or [ N I I J . On the other hand, at the North-West edge, both the J. S i l l and [SIIIJ/£NII] r a t i o s shew a ttinim'um value, sugesting that the i n c r e a s e i n the H « / H p r a t i o i n t h i s area i s not due e n t i r e l y t o e x t i n c t i o n by dust. 145 T a i l e XVI NGC 2440: E x t i n c t i o n values max min < > i + 10. 31 4. 23 5. 16 E (H«-H^) 1 .40 0.43 0.64 E (B-V) c j A v I h - 4 I 1.79| 3,88 I 0.55| 1.19 I 0.81| 1.76 I 1.21 0.37 0-55 A (Hp) 4.47 1.37 2.03 I 146 F i g u r e 21 NGC 2440: Schematic s t r u c t u r e (See next page f o r d e t a i l s ) 147 Figure 2J NGC 2440: Notes HI £SIIIJ x x * x x x HI min "r~r~r^> H«/Hp Max ^ a. j . i. H^ /Hp, min • • • [ S I I I J / | N i l J min O-O-O- £SIII]/H<< min HI Max lV i N I i g / H ^ min Q {_ SIII j] Max 148 4. 2 NGC 3132 T h i s i s a p l a n e t a r y nebula f o r which i t i s r a t h e r d i f f i c u l t t o f i n d i n f o r m a t i o n i n the l i t e r a t u r e . N e v e r t h e l e s s , Torres-Peimbert et a l . . (1977) have p u b l i s h e d p h o t o e l e c t r i c photometry from the [ O i l ] doublet a t 3727 t c the iOIIi] doublet at 7325A ,. Walker (1970) p u b l i s h e d e l e c t r o n o g r a p h i c photographs at s e v e r a l wavelenths i n the blue and yellow part of the spectrum,„ Cahn (1976) has r e p o r t e d an e l e c t r o n temperature, Te, of 9600K.„ But the most important i f e a t u r e of t h i s o b j e c t and the lone t h a t has a t t r a c t e d a l o t of a t t e n t i o n l a t e l y i s the f a c t t h a t the c e n t r a l s t a r of t h i s nebula (HD 87892) has too l a t e a s p e c t r a l c l a s s (AO) to account f o r the i o n i z a t i o n of the nebula, Kohoutek and Lausteen (1977) d i s c o v e r e d a f a i n t blue, v i s u a l companion to HD 87892 whose p h y s i c a l c h a r a c t e r i s t i c s would make i t the e x c i t i n g s t a r of the nebula and Mendez (1978) has p o i n t e d out t h a t , apart from NGC 3132, there are s e v e r a l s p e c t r o s c o p i c and a l s o one e c l i p s i n g binary among p l a n e t a r i e s . F i g u r e 22 presents our 200x200 CCD data f o r t h i s o b j e c t . The f o u r images have been magnified t w i c e . The J. S I I I j] image shows f r i n g i n g superimposed cn i t , and again the J. N i l i] image has the l a r g e s t dimensions. , Another i n t e r e s t i n g f e a t u r e i s 1 4 9 the v a r i o u s knots t h a t are v i s i b l e along the r i n g . Tiery d i s t i n c t i v e knots are n o t i c e a b l e i n the Bp, H ^ , and £ S I I I J images which do not show up at a l l i n the [ N i l ] image. These are zones of high e x c i t a t i o n . , That they are zones of high e x c i t a t i o n i s deduced from F i g u r e 23a which shows the { N I I j / H ^ r a t i o . . In t h i s r a t i o a l l of these correspond to areas of minimum value f o r t h i s r a t i o . T h i s image a l s o shows t h a t the degree of e x c i t a t i o n decreases s t e a d l y outwards, the J_NIIi]/ H,< r a t i o reaches i t s maximum value i n the outer p a r t of; the nebula. The c o l o r excess E ( H c < - H ^ ) , as given by the H ^ / H ^ r a t i o , i s f a i r l y uniform across the fa c e of the nebula, except f o r a gradual i n c r e a s e from East to West, Table XVII gi v e s i n f o r m a t i o n r e l a t e d to the dimensions and i n t e n s i t i e s found i n t h i s nebula. 150 (c) [H IT ] (d) J.SIII] 1 5 1 ( C ) iSIIIJ/£NIIJ Table XVII NGC 3132: Dimensions and i n t e n s i t i e s Dimensions I ^ i _ i _ _ _ _ _ _ I t N I I J I I l s i n J Major Axis ~ r | 56 T" T | 62 _ j . _ _ _ _ _ _ _ I 68 1__ 57 (arcsec) 1 1 I I Minor Axis 1 36 1 41 | 54 1 42 (arcsec) J J i i ** 1 0.04 | 0,10 | 0.06 j 0.04 ** = Surface brightness at the edge of nebula as % of peak brightness The z e r o - p o i n t of these r a t i o s was determined i n a d i f f e r e n t way from the one used f o r NGC 2440. Based on the good agreement t h a t we obtained f o r NGC 2440 between our o b s e r v a t i o n s and the p h o t o e l e c t r i c ones, we have a p p l i e d the same type of c o r r e c t i o n to t h i s data. Again, the [ N I I J /Hp( r a t i o does not need changes because we are assuming t h a t the response of the system and e x t i n c t i o n c o r r e c t i o n s are the same fo r these two l i n e s . Mendez (1978) rep o r t e d a value of 1.91 f o r t h i s r a t i o without r e a l l y g i v i n g any d e t a i l t o which aperture s i z e was used. T h e r e f o r e , we w i l l use i t as a g e n e r a l guide only. . Our r e s u l t s are as f o l l o w : min max < > [ N I I J / H t f 1.00 3. 12 2.22 For the Hc< / H p r a t i o the p e r t i n e n t data i s presented i n T a b l e X V I I I . 1 5 4 Table XVIII NGC 3132: E x t i n c t i o n values 155 4.3 NGC 324 2 T h i s i s another w e l l s t u d i e d nebula which has s e v e r a l p c i n t s of i n t e r e s t . I t has a d o u b l e - r i n g s t r u c t u r e with major and minor a x i s of 26 and 16 a r c s e c (inner r i n g ) , i n a p o s i t i o n angle of 145° . The o u t e r , f a i n t e r envelope shows dimensions of about 40 by 35 a r c s e c . O ' D e l l (1963) , Czyzak (1966) , and Torres-Peimbert e t a l . (1977) have presented p h o t o e l e c t r i c photometry, while filler (1956) p u b l i s h e d a contour map c f a Hc<+ J.NII] image of t h i s nebula. As mentioned i n Chapter I, t h i s nebula shows very weak [NIIi] emission, otherwise i t shows a t y p i c a l spectrum of a high-excj.tation nebula ( l i n e s of H e l l , CIV, and [ A r v g ) . J Our o b s e r v a t i o n s are presented i n F i g u r e 24. The four images are 200x200 frames magnified t w i c e . In t h i s case the i S I I I i ] image i s p r a c t i c a l l y f r e e of f r i n g i n g noise and i t i s the best photograph t h a t we obtained f o r any c b j e c t a t t h i s wavelength. Emission i s mainly concentrated i n knots along the inner r i n g ; i t has a d i s t r i b u t i o n s i m i l a r to that f o r hydrogen, but due to the d i f f e r e n c e i n abundances, the hydrogen emission f i l l s p r a c t i c a l l y the whcle nebula. The [ N i l ] image shows a change i n s t r u c t u r e . I t i s 156 concentrated i n the i n s i d e of the i n n e r r i n g only. The f a c t t h a t we do not see the two b r i g h t e s t condensations along the major a x i s of the i n n e r r i n g i n t h i s l i n e , although they are very n o t i c e a b l e i n the ether l i n e s i s i s an i n d i c a t i o n t h a t these two r e g i o n s are zones of high degree of e x c i t a t i o n . T h i s s i t u a t i o n becomes more obvious when c o n s i d e r i n g the r a t i o s presented i n F i g u r e 25, 1 5 7 158 Dimensions and i n f o r m a t i o n r e l a t e d with F i g u r e 24 i s given i n Table XIV. F i g u r e 25 shows the l i n e r a t i o s obtained frcm t h i s data. The Hof/Hp r a t i o shows a remarkable a n t i c o r r e l a t i o n with the hydrogen em i s s i o n , showing that the o p t i c a l appearence i s again determined by the presence of opaque m a t e r i a l which o b s t r u c t s the l i g h t coming, f o r example, frcm the i n n e r s h e l l . E x t i n c t i o n i n c r e a s e s outward i n a l l d i r e c t i o n s . The J_ N i l jJ/Ho( r a t i o shows an i n c r e a s e i n i t s value at t o t h ends of the major a x i s . T h i s o b s e r v a t i o n agrees with r e s u l t s by Hawley e t a l . (1977), who found an enhacement of the [ N i l ] l i n e s near the edge of the Eing Nebula. The s t r o n g emission seen around the c e n t r a l s t a r must be i n part due to contamination by s t e l l a r r a d i a t i o n . 159 (c) [ S I I I J/[NII J (a) { .SIIIO/K^ Table X I X NGC 3 2 4 2 : Dimensions and i n t e n s i t i e s Dimensions h Major Axis (arcsec) Minor Axis (arcsec) Outer r i n g ** fl* I [ N I I J I J. —(-2 6 I 2 5 I 2 6 16 I 14 I 1 4 60 0 . 0 7 | 0 . 0 1 I 0 , 3 3 £ s i n j -+ i 2 6 1 6 0, 1 3 ** = Surface b r i g h t n e s s at the edge of nebula as % c f peak b r i g h t n e s s 161 The z e r o - p c i i r t c a l i b r a t i o n was done i n a s i m i l a r way as f o r NGC 2440. Kaler e t a l . (197 6) have r e p o r t e d a value of 3.54 f o r the i n t e g r a t e d H « / H p r a t i o . For t h i s same r a t i o , Barker (1978a) gave a value of 2.99., Our value f o r a diaphragm of 30 a r c s e c centered i n the nebula i s 6,43. T h e r e f o r e , the n o r m a l i z a t i o n f a c t o r i s of the order of 0.55 (adopting K a l e r ' s r e s u l t ) , g i v i n g an agreement cf about 40 % with the value of 0.4 found f o r NGC 2440 and 0.58 from F i g u r e 2. Table XV presents the summary o f the e x t i n c t i o n values f o r t h i s nebula. Maximum and minimum values are defined f o r the i n n e r s h e l l o nly. 162 .Table XX NGC 3242: E x t i n c t i o n values i 1 1 T r 1 1 1 I I I I 1 I I I I I Htf/Hp | E f r k - H p ) | E(B-V)| A ( H p ) ! C | Av j j Max | 8.50 | 0.54 | 0.47 | 2.04 j 0,82| 1.50 | I I 1 I I I I I | Min | 4.50 | 0.00 | I I j I i i i i i i i i | < > | 6.50 | 0.25 | 0.22 | 0,95 I 0.38J 0.70 | i I I I I I I I 1 6 3 The r e s u l t s f o r the [ N I I ^ / H * r a t i o are presented below; min max < > £NIIJ / H o ( 0.006 0,026 0,011 Torres-Peimbert et a l . (1977) have r e p o r t e d a value of 0.011 F i g u r e 26 i s a composite;image o f t h i s nebula, where we have put together most of the i n f o r m a t i c n a v a i l a b l e from F i g u r e s 24 and 25. The i o n i z a t i o n s t r u c t u r e comes up c l e a r l y i n t h i s case. F o r example, the maximum values f o r the £ S I I I a n d the £ N I I ] / H o ( r a t i o s are j u s t one behind the other, c o n f i r m i n g the idea cf a gradual decrease i n i o n i z a t i o n as a f u n c t i o n o f d i s t a n c e from the s t a r . In order to understand the [ N i l ] emission d i s t r i b u t i o n we have to assume that the abundance of J.NIIJ] drops o f f very r a p i d l y i n the outer envelope of the nebula. T h i s i s the opposite s i t u a t i o n to the one o c c u r r i n g i n NGC 2440 and NGC 3132. But, t h i s s i t u a t i o n can be understood i f we c o n s i d e r t h a t NGC 3242 i s a d e n s i t y bounded nebula (see F i g u r e 24b). In t h i s case, l i t t l e or no emission from l o w - i o n i z a t i o n l i n e s should be coming from the c u t e r regions and the observed emission i s being produced i n f i l a m e n t s and condensations tfcat are i n the nebular s h e l l . A l l of our p i c t u r e s show evidence of s t r a t i f i c a t i o n and there i s s p a t i a l o v e r l a p between the hydrogen, £SIIIi], and [ N i l ] emissions. 164 Fijgure 26 NGC 3242: Schematic s t r u c t u r e (See next page f o r d e t a i l s ) 165 Figu r e 26 NGC 3242: Notes x * * x outer s h e l l (HI) in n e r s h e l l (HI) x o x o x o x i n n e r s h e l l (i. N i l 3) HI Max H I Min [ S I I I J Max r-Ti—T\ H*/Hp Max i N i l Max £SIII3/Hc{ Max 166 V. SOMMABY AND CONCLDSIONS In t h i s t h e s i s , we have d e a l t with the a p p l i c a t i o n o f multi-element sensors to the study bf gaseous nebulae., The advantage of using t h i s type of d e t e c t o r ( e. g. Large dynamic range and array s i z e s ) can be f u l l y e x p l o i t e d o n l y i f the proper data r e d u c t i o n f a c i l i t i e s are a v a i l a b l e . A Ccmtal V i s i o n I Imaging System i s used s u c c e s s f u l l y f o r d i s p l a y i n g images up to 256x256 p i x e l . . I t i s shown that pseudo-color technigues give a very e f f e c t i v e p r e s e n t a t i o n of the i n f o r m a t i o n contained i n an image. \ Four p l a n e t a r y n e i u l a are s t u d i e d i n d e t a i l . . V a r i a b l e e x t i n c t i o n a c r o s s the f a c e of the nebula i s shown to e x i s t f o r a l l of them._ S t r a t i f i c a t i o n of the r a d i a t i o n , l o c a l d e n s i t y f l u c t u a t i o n s , and a two envelope s t r u c t u r e are a l s o common f e a t u r e s of these f o u r o b j e c t s . The e x i s t e n c e of v a r i a t i o n s i n the c o l o r excess E (H*-H^) i s an important o b s e r v a t i o n a l r e s u l t , because p a r t i a l o b s c u r a t i o n has been assumed i n order to e x p l a i n the e x t i n c t i o n of the t o t a l r a d i a t i o n coming from p l a n e t a r y n e t u l a e (Seaton 1979) . I t supports the idea of a dust component o u t s i d e the HII Eegion of the nebula. 167 The f a c t t h a t the c o l o r excess, E(Ho<-Hp), i n c r e a s e s outwards i n d i c a t e s the presence of matter around the p l a n e t a r y nebulae and t h a t t h i s matter (dust, molecules, and gas) i s conce n t r a t e d more i n the outer than i n the i n n e r envelope. I t i s known t h a t many red g i a n t s s t a r s c o n t a i n dust, molecules, and a s h e l l s t r u c t u r e (Morris 1975) . The remnants of such c i r c u m s t e l l a r envelopes have been observed i n three p l a n e t a r y nebulae (Mufson e t a l . , 1975), Thus, our o b s e r v a t i o n s confirm the a s s o c i a t i o n of n e u t r a l m a t e r i a l with p l a n e t a r y nebulae. The d e t e c t i o n cf molecular hydrogen i n f i v e p lanetary nebulae by Beckwith e t a l . , (1978) f u r t h e r supports the e x i s t e n c e of an expanding s h e l l of molecules, gas, and dust which i s r e s p o n s i b l e f o r the observed v a r i a t i o n i n e x t i n c t i o n and seme of the i n f r a - r e d and r a d i o emission detected towards p l a n e t a r y nebulae. P h i l l i p et a l . (1977) p u b l i s h e d models f o r nebular s h e l l s thrown o f f from s p i n n i n g c e n t r a l s t a r s . , These models p r e d i c t a c o n c e n t r a t i o n of nebular m a t e r i a l towards the p c l e s of an o b l a t e s p h e r o i d a l s h e l l . T h i s c o n f i g u r a t i o n i s seen i n a l l of our o b j e c t s , g i v i n g support to the e j e c t i o n o f the nebular envelope from a r o t a t i n g s t a r . S t r u c t u r a l d i f f e r e n c e s and e x c i t a t i o n c o n d i t i o n s i n the 168 nebula are c l e a r l y seen when comparing l o w - i o n i z a t i o n l i n e s , e. g [NI I J , [SII,], with a h i g h - i o n i z a t i o n l i n e such as Hc(, or [ S I I I J . Boeshaar (1S74) showed t h a t s m a l l - s c a l e inhomogeneities, s p e c i a l l y knots and bl o b s , show s t r o n g emission o f nebular t r a n s i t i o n s of n e u t r a l and s i n g l e i o n i z e d atoms. These zones are c o n s i s t e n t l y c o o l e r and denser than t h e i r surroundings. In t h i s c o n t e x t , our data shows t h a t a wide range of i o n i z a t i o n e x i s t s i n the same r e g i o n of gas. Also, we are able t c d e t e c t nebular condensations which are h i g h l y i c n i z e d because they are very strong i n the He/, and 4.SIII1] l i n e s but not i n the [NIIj] l i n e . These condensations must be p a r t i a l l y i c n i z e d blobs, the i n s i d e being n e u t r a l , the i o n i z a t i o n f r o n t p e n e t r a t i n g fromj the o u t s i d e . A s i m i l a r if s i t u a t i o n i s known to e x i s t i n th e * O r i o n Nebula (Lagues e t a l . 1979), For NGC 2440 and NGC 3132 the r a t i o J.NIIi]/Htf i n c r e a s e s outward, showing t h a t the degree of e x c i t a t i o n i n the nebula decreases outward and the e x i s t a n c e of an i o n i z a t i o n f r o n t i n the cuter part of the nebula. The very sharp outer edges, with the i o n i z e d gas l y i n g i n s i d e , t h a t NGC 2440 and NGC 7027 show i n the north-west and south-west d i r e c t i o n r e s p e c t i v e l y , are a l s o evidence t h a t i n these d i r e c t i o n s we are d e t e c t i n g the t r a n s i t i o n zone between 169 the HII Region and the HI Region surrounding i t , NGC 2440 i s a very unusual p l a n e t a r y nebulae. Apart ircm having very s t r o n g [ N i l ] and no c e n t r a l s t a r v i s i b l e , i t has an asymmetric, patchy s t r u c t u r e . In t h i s r e s p e c t i s very s i m i l a r t o M1-41 and M1-67, M1-67 has a Wclf-Rayet s t a r of the n i t r o g e n sequence as a nucleus ( B e r t o l a 1964) and Dopita (1S77) has sugested that the nucleus of M1-41 i s a l s o a Wolf-Bayet s t a r of the n i t r o g e n sequence. C o n s i d e r i n g t h a t a l l c e n t r a l s t a r s of p l a n e t a r y nebulae o f type Wolf-Rayet are of the carbon sequence and because of i t s l a r g e expansion v e l o c i t y (~70 kmsec - 1) , f i s m i s (1979) has concluded t h a t M1-67 should be c l a s s i f i e d as an HII Region r a t h e r than as a pla n e t a r y . But, i f we def i n e a p l a n e t a r y nebula as a nebula formed by e j e c t i o n of gas from a c e n t r a l s t a r which i s not a nova or a supernova (Pismis 1979), then M1-41 and M1-67 are p l a n e t a r i e s and the nature of NGC 2440 co u l d be e x p l a i n e d under the assumption that the unseen c e n t r a l s t a r i s a l s o a Wolf-Rayet s t a r of the n i t r o g e n sequence. By s t u d y i n g the n e a r - i n f r a r e d spectrum cf NGC 7027 we were able to show that models t h a t i n c l u d e charge t r a n s f e r r e a c t i o n s with hydrogen f o r s e v e r a l i o n s g i v e a good agreement with o b s e r v a t i o n s of both high and low i o n i z a t i o n p o t e n t i a l l i n e s . Doublets of nebular importance, e.g. [SIIIi] 9069,9532 1 7 0 and [ N l l i ] 6548,6584, were determined with a higher accuracy than any work done i n the past and a b e t t e r agreement between ob s e r v a t i o n s and theory was obtained. Because of the experimental stage of some of t i e d e v i c e s used i n t h i s r e s e a r c h , seme of the i n i t i a l g o a l s of t h i s program were not f u l l y accomplished. . Paschen and Pfund decrements should be obtained because they are the best i n d i c a t o r s f o r the value of Ne i n the densest part of the nebula (permitted l i n e s are not quenched i n t h i s r e g i o n ) . B i b l i o g r a p h y A l l e n , C.W„ 1964, 11 A s t r o p h v s i c a l q u a n t i t i e s " , (Oniv. of London) . A l l e r , L.H., L i l l e r , W. 1968, i n "Planetary nebulae, s t a r and s t e l l a r systems". V o l V I I , p.483. . A l l e n , D.A. 1979, M.N. E. A. S. 186 , 1P. . A l l e r , L.H. 1956, "Gaseous Nebulae" ,(London, Chapman & H a l l , LTD.) A l l e r , L. H. .1957, Ap.J., J 2 5 , 84. A l l e r , L.H., Czyzack, S.J., K a l e r , J.B. 1968, Ap. J . , 151 187. A l l e r , L.H., Walker, M.P. 1970, Ap.J., 161, 917. 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Whit f o r d , A. E. 1958 , A. J . , 63 , 201., Wilson, O.C. .1950, A p. J. , 111 , 279., 178 Appendix I A l l the data a c q u i r e d with the l i n e a r E e t i c o n arrays was reduced with a F o r t r a n coded program, PGILSEEC , which was w r i t t e n by J . Glaspey. . POLL-SPEC i n c l u d e s simple a r i t h m e t i c o p e r a t i o n s used t o remove dark s i g n a l , sky background, and in s t r u m e n t a l response v a r i a t i o n s . The main drawback with POILSPEC i s i t s l a c k of any i n t e r a c t i v e c a p a b i l i t y . T h i s program i s now o b s o l e t e as an i n t e r a c t i v e F o r t r a n coded program, RETICENT , developed by C. P r i t c h e t and S. Yang i s c u r r e n t l y i n use f o r the r e d u c t i o n of s p e c t r c p h o t c m e t r i c data. The two-dimensional data was reduced with a software package, CTIO , i n i t i a l l y developed ty C. P r i t c h e t s p e c i f i c a l l y f o r the CCD data. T h i s package i n c l u d e s s u b r o u t i n e s a l l o w i n g a number of simple a r i t h m e t i c o p e r a t i o n s cn or between data frames, and a l s o , more complicated t a s k s such as smoothing, s h i f t i n g , and contour maps ( P r i c h e t 1979). When the Comtal Imaging System became a v a i l a b l e f o r use i n January 1979, i t was necessary t o i n c l u d e i n t h i s package sub r o u t i n e s t h a t would t r a n s f e r data from the main computer on campus to the Comtal System v i a an HP21MX minicomputer. (Figure 27), T h i s e x t e n s i o n of the r e d u c t i o n program was r e s p o n s i b i l i t y of t h i s candidate. 179 In what f o l l o w s , the f o l l o w i n g convention w i l l he used: IX : data a r r a y , INTEGEE*2 . NX : l i n e l e n g t h of data a r r a y . I • ft : 60 byte comment blo c k . 1X0, IY0 : x, y s t a r t i n g l o c a t i o n f o r the a c t i o n of a command. IDX, IDY :dx, dy range f o r a command. . NCONT : no. of contours. MIN : Minimun value to be p l o t t e d . The complete set of subrou t i n e s i s found i n the f i l e : AECE : CTIO ( F o r t r a n Source) and &BCB : LIB (Object, L i b r a r y f i l e ) T h i s f i l e c o n t a i n s the i n i t i a l PBITCHET : CTIO program plus the f o l l o w i n g subroutines: i) Subroutine ADD (IX,NX,NADD) Constant term N ADD i s added to each element cf array IX (NX,NX) i i ) Subroutine MULT (IX,NX,MOLT) Each element of a r r a y IX(NX,NX) i s m u l t i p l i e d by contant term MOLT. i i i ) Subroutine WREATA (A,IX,NX,IX0,IY0,IBX,IDY) Array IX (NX,NX) i s w r i t t e n cn p r i n t e r (unit=6). iV) Subroutine MEAN (IX,NX,IX0,IY0,IDX,IDY) 180 P r i n t Mean and standard d e v i a t i o n f o r array IX (NX,NX) VI) Subroutine CENTER (IX,NX,NX ,IZ) Center array IX(NX,NX) i n an IZ(256,256) a r r a y . VII) Subroutine CCMTA1 (A,IX,IZ) Array IX (256,256) i s s t o r e d i n a r r a y IZ (256,256) with an 8 b i t r e s o l u t i o n (dynamic range of 256:1) VIII) Subroutine FTT2 (IX,NX,IX0,IY0,IDX,IEY,IFILT,IZ,IW) Two-dimensional Log Power Spectrum d i s t r i b u t i o n . I f IFILT * 0 , a c o s i n e - b e l l t a p e r i n g to Nyguist frequency i s done. T h i s s u b r o u t i n e i s l i m i t e d t o IDX,IDY < 64, T h i s can be a l t e r e d by changing a l l occurrences of "64" and "32" i n the f i r s t seven l i n e s of the subroutine. The two types of output : IZ, IW d i f f e r i n the l o c a t i o n of the z e r o - p o i n t . F c r best r e s u l t s always Smooth the power spectrum. IX) Subroutine FIEM (IX) Read SM71: FIEM 50x50 array data; t h u s , CTIO package can be a p p l i e d to t h i s data. X) Subroutine LPGCNTR (IX,N X ,IX0,IY0,IDX,ID Y, NCONT ,MI K ,IY) Contour p l o t of a r r a y IX(NX,NX) i n a Log s c a l e . T h i s subroutine was w r i t t e n by P. Monger. F i g u r e 27 0. E. C. Data System Magnetic Tape I nterective Terminals MP21MX COMTAl V 1 S ION ONE | HP2645A • Coniole Track Bo 

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