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Carbon stars in the large magellanic cloud 1976

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CARBON STARS IN THE LARGE MAGELLANIC CLJUD by Dennis Richard Crabtree B.Sc. University of B r i t i s h Columbia, 1974 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in the Department of GEOPHYSICS and ASTRONOMY We accept t h i s thesis as conforming to the required standard. The University of B r i t i s h Columbia August, 1976 © Dennis Richard Crabtree 1976 In p resent ing t h i s t he s i s in p a r t i a l f u l f i l m e n t o f the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e fo r reference and study. I f u r t h e r agree that permiss ion fo r ex tens i ve copying of t h i s t he s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r ep re sen ta t i ve s . It i s understood that copying or p u b l i c a t i o n of t h i s t he s i s f o r f i n a n c i a l gain s h a l l not be al lowed without my w r i t t e n permis s ion. Depa rtment The Un i v e r s i t y of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1WS i i Abstract A catalogue of cool carbon stars i n the Large Magellanic Cloud i s presented along with photometric and spectroscopic observations of some of the members. Image tube spectra at a dispersion of 117 A/mm were obtained for seven of the stars i n order to investigate some of the grosser features of the spectrum. In addition photometric observations on the VEI system of forty stars have been made. The spectra indicate that three of the carbon stars observed show enhancement of spectral features involving the l 3C isotope. Using the photometric observations to place the stars in a t h e o r e t i c a l Hertzsprung-Hussell diagram, i t i s concluded that (1) a l l forty stars are i n the double-shell sourca phase of evolution and, (2) the helium s h e l l flashes are responsible for the formation of the majority of cool N-type carbon stars. v i i i Table of Contents page I I n t r o d u c t i o n 1 I I Catalogue of Carbon S t a r s 5 I I I Photometric Observations 66 IV S p e c t r o s c o p i c Observations 76 V Carbon S t a r s i n the H-B Diagram 87 VI Summary 98 B i b l i o g r a p h y 101 i v L i s t of Tables page I. P l a t e Centres 8 I I . Carbon Star Coordinates 9 I I I . Carbon Star Photometry 67 IV. S p e c t r o s c o p i c Observations 79 V. P r o p e r t i e s of the Seven Carbon S t a r s 81 VI. C l a s s i f i c a t i o n of Carbon S t a r s 82 L i s t of F i g u r e s page 1. F i n d i n g Charts 27 2. V versus R-I 70 3. V versus V-I 71 4. V versus V-E 72 5. Mbol versus V-R 74 6a. Carbon Star S p e c t r a , r e g i o n 1 77 6b. Carbon S t a r S p e c t r a , r e g i o n 2 78 7. Bolometric C o r r e c t i o n s 88 8. Colour Temperature versus R-I 92 9. T h e o r e t i c a l H e r t z s p r u n g - R u s s e l l Diagram 93 v i Acknowledgements I would l i k e to thank my supervisor Harvey fixcher for his patience and enthusiastic support during the course of t h i s work. I thank B.I. Olson for supplying many of the computer programs used i n t h i s study. I also thank B.E. Westerlund for kindly supplying the o r i g i n a l charts on which he had marked the suspected program stars. I thank the University of B r i t i s h Columbia for support from a postgraduate fellowship. F i n a l l y I would l i k e to thank the graduate students of the department for making the department such an enjoyable place to work. 1 I I n t r o d u c t i o n Among the s t a r s c l a s s i f i e d as red g i a n t s there are many groups which show anomalous abundances of c e r t a i n elements. One of these groups i s the carbon s t a r s . These s t a r s show an enhancement of a b s o r p t i o n bands of CH,CN, and i n c l u d i n g , i n some cases, bands of molecules i n v o l v i n g the 1 3 C i s o t o p e . In the Henry Draper Catalogue these s t a r s were o r i g i n a l l y c l a s s i f i e d as type R or N; N being reserved f o r the redder members. Shane (1928) r e c l a s s i f i e d these i n t o s u b d i v s i o n s but i t was d i s c o v e r e d l a t e r t h a t t h i s system was not a t r u e temperature sequence as was the r e s t of the Henry Draper system. Subsequently Keenan and Morgan (1941)• proposed the C- c l a s s i f i c a t i o n f o r carbon s t a r s based on temperature and carbon abundance. However t h i s system of c l a s s i f i c a t i o n has by no means s o l v e d the c l a s s i f i c a t i o n problem. Any c l a s s i f i c a t i o n system t h a t i s t o be s u c c e s s f u l must be a b l e to s o r t out the many d i f f e r i n g abundances as w e l l as the temperature sequence i n these s t a r s . Xamashita(1967) has devised a system i n which he es t i m a t e s the i n t e n s i t i e s of eleven s p e c t r a l f e a t u r e s as w e l l as c l a s s i f y i n g each s t a r cn the C c l a s s i f i c a t i o n system. One d e f i c i e n c y of the C system i s t h a t the sequence from C5-C9 probably does not r e p r e s e n t a t r u e temperature sequence ( Richer 1971 ;Scalo 1973) . Much of the t h e o r e t i c a l work on carbon s t a r s has been hampered by the l a c k of good absolute v i s u a l magnitudes f o r 2 i n d i v i d u a l o b j e c t s . Seme r e s u l t s do e x i s t ( Gordon 1968;Eicher 1972,1975;Olson and Richer 1975) but the number of s t a r s i n v o l v e d i s not l a r g e enough to cover a l l the s p e c t r a l subtypes and p e c u l i a r i t i e s observed i n these o b j e c t s . T i n s f o l l o w s from the f a c t that these o b j e c t s are r e l a t i v e l y rare i n our Galaxy, attempts t o measure the a b s o l u t e magnitudes of i n d i v i d u a l o b j e c t s run i n t o the usual s o r t of problems encountered i n t h i s endeavor; no o b j e c t i s c l o s e enough to have a r e l i a b l e t r i g o n o m e t r i c p a r a l l a x , carbon s t a r s are r a r e l y members of c l u s t e r s , few are members of binary systens, the i i l s o n - B a p p u e f f e c t i s d i f f i c u l t to use f o r the R s t a r s and i m p o s s i b l e to use f o r the N s t a r s , e t c . The absolute magnitude problem i s closely related to the problems of the e f f e c t i v e temperature and r a d i i or carbon stars. Only two carbon stars have had t h e i r angular diameters measured by the method of lunar occultation, 19 Psc and X Cue. A d i r e c t measurement of the radius i s d i f f i c u l t since no carbon star i s a member of an e c l i p s i n g binary nor has a measurable parallax. The temperature classes of the l a t e r stars in the C c l a s s i f i c a t i o n do not correlate well with the colour temperatures that have been obtained by Mendoza and Johnson (1965) ; Richer (1971) or Wing (1967) from extensive photometric observations. Colour-colour relations have shown that the cool carbon stars radiate more l i k e black-bodies than do M giants {Bahng 1966;Scalo 1973). Therefore any attempt to use a c a l i b r a t i o n between colour and e f f e c t i v e temperature that i s based on normal M giants should be treated with caution. 3 Hallerstein(1973) gives a good review of the physical properties of carbon stars as well as one possible evolutionary seguence. The carbon stars are believed to be well evolved stars that are exhib i t i n g the products of nucleosynthesis i n t h e i r outer atmosphere. The f i r s t part of this thesis contains a calalogue of carbon stars i n the Large Magellanic Cloud. A catalogue of these stars should be a very useful ' document now that several large telescopes- are becoming operational i n the southern hemisphere. If one obtains accurate absolute magnitudes and good medium dispersion spectra of carbon stars i n the Large Magellanic Cloud i t should be possible to better locate these stars i n current evolutionary models. Along with the catalogue, photometric observations on the VBI system of forty stars are presented together with image tube spectra of seven of the brighter members. Using the best available data for bolometric corrections'and'the r e l a t i o n between photometric colour and e f f e c t i v e temperature, these stars are placed i n a t h e o r e t i c a l Hertzsprung-Russell diagram. The res u l t s are compared with current models of the cool carbon stars. The medium dispersion spectra of the seven•brighter members indicate that three of the seven show enhancement of molecular bands containing the l 3 C isotope. A detailed discussion of the spectra i s presented i n section IV of t h i s t h e s i s . The catalogue i t s e l f i s presented i n section II while the 4 photometric observations are discussed in section I I I . Section V contains a discussion of the Hertzsprung-Russell diagram with respect to the carbon stars while section VI contains a summary of the r e s u l t s . 5 II Catalogue of Carbon Stars The most e f f i c i e n t way to discover and c l a s s i f y a large number of objects i s to use an objective prism survey. This method i s p a r t i c u l a r l y useful in the search for objects whose spectra are e a s i l y separable from most other astronomical spectra. Such objects include emission l i n e stars, planetary nebulae and carbon stars. The stars discussed below were i d e n t i f i e d by Dr. B.E. Hesterlund who has kindly supplied charts oi the Large Magellanic Cloud marking suspected carbon stars on them. Dr. westerlund i d e n t i f i e d these stars from 2100 A/mm I-N objective prism plates obtained with the 20/26 inch Schmidt telescope at the Uppsala Southern Station on Mount Stromlo. Carbon stars are much brighter i n the I band than either the B or V bands, thus the reason for using 1I-N plates. This also reduces the overlap of"spectra on the plate since most other stars are much fa i n t e r (absolutely) i n t h i s region of the spectrum. The plates obtained reached to about 1=14 magnitude and the carbon stars were i d e n t i f i e d using the c r i t e r i a established by .Nassau (cf. Mavridis 1967). The main indicators used to i d e n t i f y these stars were the CN bands at ^7945 A, ^8125 A and ^8320 A. Other CN bands shortward of the atmospheric A-band { )\7600 A) appear only when the spectrum i s heavily overexposed. Hesterlund(1964) has given a preliminary discussion of t h i s plate material emphasizing the d i s t r i b u t i o n of the carbon stars 6 within the Large Magellanic Cloud. He found that the carbon stars tend to avoid the central regions as well as the regions r i c h i n nebulosity and in blue stars. He also noted that they appear t c form clusterings, possibly i n the shape of arms , and that the position of these clusterings agreed well with the st r u c t u r a l features noted by de Vaucouleurs(1955) on heavily exposed photographs* Westerlund also estimated that the mean apparent visual magnitude was 15.7± 0.5. The chart material consisted of two separate sections. The f i r s t section was at a scale of about 11.8" arc/mm while the second section, which also included a l l the f i r s t section, was at a scale of 27" arc/mm. The f i r s t set was measured i n May 1974 while the second set was measured i n August 1975. The method used to get frcm the X,Y position to right ascension and declination on the sky i s that described by Smart (1971). B r i e f l y , i t consists of considering the tangent plane and a star's projected position on t h i s plane i f the telescope i s not pointed d i r e c t l y at t h i s star (as in a photograph). The point at which the tangent^plane contacts the c e l e s t i a l sphere(the point at which the telescope i s aimed) i s taken to be the o r i g i n . If ue take the meridian of this point, i t projects into a straight l i n e on the tangent plane. This l i n e forms one axis for an orthogonal coordinate system on the sky. The other axis i s taken to be a l i n e drawn perpendicular to the f i r s t a xis. The standard coordinates of the image of the star on the photographic plate are found with reference to rectangular axes drawn through the centre of the plate and drawn p a r a l l e l to the 7 orthogonal axes on the sky. By using three standard reference stars, the plate constants r e l a t i n g the measured X-Y positions to the standard coordinate system can be calculated. Once the plate constants have been evaluated i t i s an easy matter to go from X-Y values to standard coordinates co eguatorial coordinates. The f i r s t set of charts were measured on a standard drafting table using a drafting sguare and a millimeter ruler To check the accuracy of the measurements each chart was measured twice and the resulting coordinates averaged together. The second set of charts were measured on the X-Y d i g i t i z e r of the Department of Mechanical Engineering at UBC. In order .to check the accuracy of the transformations the X-Y positions of three bright reference stars were measured at the same time the positions of the suspected carbon stars were measured. After the transformation to right ascension and declination had been completed the computed coordinates of the reference stars were compared to those tabulated in the SAO catalogue. In both sets of charts the coordinates are good to about 10" arc. This accuracy was confirmed, as a l l the stars were found quite e a s i l y at the telescope. Table I contains the approximate plate centres of each of the f i e l d s as well as the number of stars measured and the number of stars for which photometry was obtained. Table II contains a l i s t of the coordinates for the epoch 1975.0 of a l l the suspected carbon stars. Finding charts for Table I Plate Centres r ~ ? i e l d R. A. I I Dec. 1 1. I * 50 I -60O I ! 2. I *» 45 i I - 6 9 ° 1 1 3. J 4 40 I I - 7 2 0 1 1 i 4. ! 5 20 \ I i -660 I 1 5. I 5 20 j 1 -690 1 1 6. I 5 20 1 i - 7 2 0 1 i 7. I 5 50 1 I -660 1 1 8. I 5 55 1 1 -690 J 1 • 9. | 6 00 1 i t - 7 2 0 i I 20 . i 6 05 1 1 -750 1 1 2 3 . I 6 30 1 i -690 1 i 24. ! 6 40 i 1 - 7 2 0 i I -i .„..., . 1 i . . . # of Carbon 1 # of Stars stars found j Paotometry j. 29 14 18 33 24 76 3 14 36 4 • 51 3 j I 13 20 these stars are presented i n Fig. 1. The f i e l d of these finding charts i s approximately 11 * arc by 16» arc with north to the top and east to the l e f t . Table II Carbon s t a r coordinates 9 L.M.C. F i e l d #1 S t a r R i g h t A s c e n s i o n (1975) D e c l i n a t i o n (1975) 1 4 h 52™ 28 S - 66°28 !o 2 4 h 53™ 2 s -66°27 ! 0 3 4 h 58 m 36 s -66°52!4 4 5 h 0 m 12 s - 66°28 l2 5 5 h l m 19 S - 66°52!9 6 5 h 2 m 9 S • - 6 7 ° 1 8 ! l 7 5 h 2 m 17 s - 66°57!o 8 5 2 28 -67°12 l5 9 4 h 5 9™ 00 S -65°57!7 10 5 h l m 4 1 S - 6 5 ° 5 l ! 9 11 5 h 2 m 53 S -65°58!9 12- 5 h 3 m 11 S - 66°2 !9 13 5 h 2 m 47 S - 66°26!5 h m s , 14 5 3 25 -66°55.9 15 5 h 4 m 50 S ' - 6 7 ° 1 3 ! l 16 £ h 5 m 50 S -66°15'.3 17 4 h 58 m 43 S - 65°26 l6 18 4 h 58 m 32 S - 65°22 l2 . h m s ' 19 4 59 13 -64°59.0 20 5 h 0 m 26 S - 65° 2.'5 21 5 h 2 m 22 S -65° 9 ^ 22 5 h 2 m 43 S - 6 5 ° l l ! l 23 4 h 53 m 23 S -64°37!9 24 4 h 50 m 32 s -67° o!7 Table I I cont'd 10 L.M.C. F i e l d //1 S t a r R i g h t A s c e n s i o n (1975) D e c l i n a t i o n (1975) 25 4 h 4 9 m 28 s -67°16!3 26 4 h 5 0 m 3 4 s -67o10.'6 27 4 h 5 2 m 3 0 s -67°11 ! 1 .28 4 h 5 7 m 5 6 s -67°19!4 29 5*1 0 m 3 s -67°14.'5 11 Table I I cont'd L.M.C. F i e l d #2 S t a r 1 R i g h t A s c e n s i o n (1975) D e c l i n a t i o n (1975) 4 h 33 m 51 S -70°15!6 2 4 h 39 m 5 S - 7 o ° i o ! o 3 4 h 40 m 12 S -7 0°13! 1 4 4 h 49 m 48 s - 69°58 l8 5 4 h 52 m 54 s -69°57 !4 6 4 h 53 m 44 s - 6 7°4l!4 7 4 h 55 m 25 S -68°54!2 8 4 h 54 m 39 S -7 0° 2'.3 9 4 h 55 m 1 1 S -7 0° 2!8 10 4 h 55 m 43 s -7 0° l'.9 11 4 h 55 m 35 S -70° 9l7 12 4 h 58 m 39 S - 7 0 ° l l ! 3 13 4 h 59* 19 S - 7 0 ° l o ! 3 14 5 h 0 m 23 S -7 0°15!7 Table I I cont'd L.M.C. F i e l d //3 S t a r R i g h t A s c e n s i o n (1975) D e c l i n a t i o n (1975) 1 4 h 41 m 46 S -70°52 !5 2 4 h 42 m 34 S - 7 0 ° 3 9 ' 4 3 4 h 4 4* 56 s -70°31!3 4 . 4 h 4 8 m 43 s -72°28.'o 5 4 h 5 l m 9 S -72°45.'l 6 4 h 53 m 0 s - 7 3 ° 1 8 l 5 7 4 h m 50 15 s -71° 3!o 8 4 h 5 0 m 35 s -70°25!6 9 4 h 53 m 24 s - 70°38 l3 10 4 h 5 3 m I s -71°15!2 11 4 h 57 m 2 s -73°14 \5 12 4 h 55 m 28 s -70°21 '.9 13 4 h 5 6m 14 S -70°2o !o 14 4 h m 58 3 S -70 D 5o!4 15 4 h 57 m 50 S -71°21 !8 16 4 h 5 8 m 4 1 S -71°58 !5 17 " 5 h Im s 52 -7 2° 56'.6 18 5 h o m 36 S -71° 14*. 5 Table II cont'd L.M.C. F i e l d if h S t a r R i g h t A s c e n s i o n (1975) D e c l i n a t i o n 1 5 h 7 m . 8 S -64°27!.2 2 5 h 8 m . 44 s -64°42.3 3 5 h l l m 3 1 S -64 011.'9 4 5 h 1 2 m 3 1 s - 6 4 ° 1 4 ! l 5 5 h l l m 5 0 s -65° 9!8 6 5 h l l m 42 s -65°16!1 7 5 h 1 5 m 17 s -65° 9.6 8 5 h 16 m 9 S - 6 4 ° 5 2 ! l 9 5 h 1 7 m 1 0 s -64°48!5 10 5 h 1 9 m 4 5 S -65° 4.'2 11 5 h 2 3 m 2 S -64°54.7 12 5 h 4 m 5 5 S -64°30'.7 13 5 h 9 m 2 1 s -64°28:2 14 5 h 1 6 m 3 4 S -64°2l!l 15 5 h 8 m 5 4 S -65°43. !7 16 . 5 h i o m 4 4 S -65°42'. 1 17 5 h 12 m 6 S -65°47'.6 18 5 h 1 2 m 5 5 S -65°43l3 19 5 h 1 5 m 3 3 S o ' -65 47.5 20 5 h 5 m 5 9 S -65°58.8 21 5 h 7 m 46 S -66° 5.5 2 2 5 h 3 m 32 S -66°23l2 23 5 h 6 m 13 S -66°26!4 24 ' 5 h 8 m 2 4 S -66°26!8 Table II cont'd L . M . C . F i e l d #4 S t a r R i g h t A s c e n s i o n ( 1 9 7 5 ) D e c l i n a t i o n ( 1 9 7 5 ) 2 5 5 h l l m 4 4 s - 6 6 ° 5 2 l 7 2 6 5 h 6 m 4 4 s - 6 7 ° 4*.9 27 5 h 1 0 m 5 0 S - 6 7 ° 2 7 '.2 28 5 h 1 5 m 1 9 s - 6 7 ° 1 5 : 9 2 9 5 " 1 6 m 28 3 0 5 h 1 9 m 3 9 s - 6 7 0 3 6 ! 6 31 5 h 2 0 m 4 4 s - 6 7 0 3 7 ! 4 3 2 5 h 1 5 m 4 s - 6 4 ° 4 8 ! 4 33 5 h 1 4 m 1 5 s - 6 5 ° 3 ^ Table II cont'd L.M.C. F i e l d #5 Star R i g h t A s c e n s i o n (1975) D e c l i n a t i o n (1975) 1 4 h 59 m 57 S - 6 7 ° l 4 ! l 2 5 h o m 47 S -69° 9*0 3 5 h 2 m 1 0 s -68°55!6 4 5 h 2 m 7 S - 6 8 ° 4 6 ! l 5 5 h 3 m 38 s -68°35!5 6 5 h 3 m 35 S -68°19 l7 7 5 h 3 m 4 3 s -67°39\l 8 5 h 8 m 54 s -67°26!2 9 5 h 4 m 18 s -69°15!6 10 5 h 7 m 5 S -69°58!2 11 5 h 9 m 1 1 s -69°28!4 12 5 h 9 m 24 s -69°13!2 13 5 h i o m 25 S -70°24 l2 14 5 h 16m 14 S - 69°57 !1 15 5 h 18 m 49 S -70° l!9 16 5 h 2 i m 59 S -69°56 l6 17 * 5 h 24m 43 S -69°21\l 18 5 h 2 8 m s 20 - 7 0 ° 2 l ! 6 19 5 h 27 m 40 S -69° 6!8 20 5 h 27 m 20 S -67°23!6 21 5 h 2 9 m 46 S -68° 4l6 22 5 h 3 0 m 28 s -68°57\l 23 5 h 3 2 m 57 S -70°12!8 24 5 h 33 m 34 S -68°51!4 Table II cont'd L.M.C. F i e l d #6 S t a r R i g h t A s c e n s i o n (1975) D e c l i n a t i o n (1975) 1 5 h 0 m 24 S -70°15!8 2 5 h 0 m 4 6 S -70°39l4 3 5 h I m 28 S -70°38.'2 4 . 5 h 2 m 4 S -70°53!3 5 5 h 5 m 4 S -70°3o!9 6 5 h 5 m 6 S -70°27!6 7 5 h 6 m 14 s -70°19:4 8 5 h 8 m 16 s -71° 7.*8 9 5 h 1 3 m 10 s -71° K 6 10 5 11 2 7 s -70°46!l 11 5 h 1 5 m 8 S -73°17l8 . 12 5 h 16 m 8 S -73° 18.'2 13 5 h 2 6 m 4 s -73°19.'8 14 5 h 26 m 4 1 S -73° 2!8 15 . 5 h 2 8 m 4 5 S -73° ^\(> 16 5 h 24 m 4 4 S -72° 9l7 17 5 h 2 7 m 2 0 S " -72° 12.'7 18 5 32 40 -70 53.1 19 5 h 3 3 m 5 4 s -70 o53!4 20 5 h 3 5 m 10 S -71° l l A 21 5 h 3 7 m 12 s -70° 58!6 22 5 h 3 8 m 0 S -70° 4 9 ! l 23 5 h 38 14 -72° 9.3 24 5 h 3 8 m 58 S -7 2° 2*. 4 25 5 h 3 9 m 1 9 S -72°10!4 26 5 h 3 9 m 16 s -7 2° 5.'o Table II cont'd L . M . C . F i e l d #6 • S t a r R i g h t A s c e n s i o n ( 1 9 7 5 ) D e c l i n a t i o n ( 1 9 7 5 ) 27 5 h 4 1 m U S - 7 2 ° 3 0 . 7 28 5 h 3 8 m 3 5 S - 7 1 ° 3 6 . 0 29 4 h 5 9 m 5 7 s - 7 1 ° 1 ! 6 .30 5 h 2 m 2 9 S - 7 1 ° 3 ! 9 h 9 <? 1 31 5 4* 9 - 7 2 b 1 9 . 4 32 5 h 7 m 1 1 s - 7 3 ° 9 . 4 33 5 h 8 m 6 s - 7 2 ° 4 9 . ' 2 34 5 h 8 m 5 2 S - 7 2 ° 4 7 l 3 h m o ' ' . 35 5 10 7 - 7 2 ° 1 7 . 8 - 36 5 h 1 0 m 3 2 S - 7 1 ° 4 7 \$ 37 5 h 1 3 m 3 6 S - 7 0 ° 5 2 . ' 5 , 3 7 a 5 h 1 2 m 2 9 S - 7 0 o 5 0 ! 3 38 5 h 1 2 m 4 9 S - 7 1 ° 4 7 !7 39 5 h 1 3 m 5 0 S - 7 2 ° 5 5 ! l 40 5 h 1 5 m 5 5 S - 7 2 ° 3 3 ! 2 41 5 h 14™ 4 4 s - 7 1 ° 4 4 . 7 42 5 h 16™ 1 5 S - 7 1 ° 5 2 . ' 4 43 5 h 1 6 m 3 5 S - 7 2 ° 1 4 l 2 44 5 h 1 8 m 3 2 s - 7 1 ° 5 3 ! 4 45 5 h 1 7 m 3 8 s - 7 1 ° 4 U 46 5 h 1 8 m 3 3 S - 7 0 ° 5 7 l 7 47 5 h 2 0 m 2 1 s - 7 2 ° 4 3 l 3 48 5 h 2 2 ° 2 0 S - 7 2 ° 3 0 . ' 5 49 5 h 2 2 m 1 3 S - 7 2 ° 5.'3 50 5 h 2 3 m 2 6 S • - 7 1 ° 5 9 l 0 Table I I cont'd L . M . C . F i e l d #6 Star R i g h t A s c e n s i o n (1975) D e c l i n a t i o n (1975) 51 5 h 23 m 11 s -71°44!5 52 5 h 24 m 4 S -71°47!2 53 5 h 21 m 34 S -71°29.*8 .54 5 h 23 m 5 S -7 10 25 .'6 . 55 5 h 23 m 44 s - 71°34:3 56 5 K 23 m 59 S -71°27.'9 57 5 h 24m 50 S -71°26!o 58 5 h 23 m 44 s - 7 0 ° 4 5 h 59 5 h 24 m 5 6 s -71° 5!4 60 5 h 24™ 53 S -70°59!8 61 5 h 27 m 34 S -7'p058 !3 ... 62. 5h 28 m 8 S -70°55!4 h in s o ' 63 5 26 56 -70 40.3 5 h 27" 33 S -70 O 40!5 65 5 h 26 m 26 S -72°13.'5 66 5 h 30 m 47 S -72° 4!9 67 5 h 3 i m 58 S -71°44!5 68 5 h 32 m 16 S - 7 1 0 l l ! 9 69 5 h 33™ 2 s -71°32!7 70 5 h 33 m 28 S -71°34!.9 71 5 h 33 m 6 S -71°27 !8 72 5 h 34 m 6 S -71°23!o 73 5 h 33™ 53 S -72° 4 ! 9 74 5 h 34 m 37 S -71°59 ! 1 75 5 h 35 m 27 S -72° s!'7 76 5 h 38 m 4 S -70°55!9 Table II cont'd L . M . C . F i e l d #7 S t a r R i g h t A s c e n s i o n ( 1 9 7 5 ) 1 5 h 3 1 m 1 1 S 2 5 h 3 A m 2 4 S 3 ' 5 h 3 5 m 4 1 s D e c l i n a t i o n ( 1 9 7 5 ) - 6 5 ° 3 3 ! 2 - 6 7 ° 2 9 . 5 - 6 6 ° 2 1 . 8 Table I I cont'd L.M.C. F i e l d #8 S t a r R i g h t A s c e n s i o n (1975) D e c l i n a t i o n (1975) 1 5 h 44 m 3 3 s - 6 9 ° 8!6 2 5 h 48 m 2 1 s - 6 7 ° 1 4 . 5 3 5 h 4 8 m 3 s - 6 9 ° 2 2 ! 1 .4 5 h 5 2m 4 2 s - 6 7 ° 5 4 . 5 5 5 h m 53 2 5 S - 6 8 ° 4 6 ! 1 6 6 h 5 m 5 6 S - 6 9 ° 2 7 ! 2 7 6 h 7 m 4 1 S o ' -70 31 .0 8 6 h 7 m 3 3 s - 6 9 ° 2 6 . 2 9 6 h 8 m 4 3 s - 6 9 ° 5 8 \ h 10 6 h 7 m 2 3 S - 6 7 ° 5 2 l 4 11 6 h 7 m 4 1 s - 6 7 ° 5 2 l 0 12 6 h 8m 4 7 S - 6 8 ° 1 5 ' . 9 13 6 h 9 m 1 0 s - 6 7 ° 1 2 l 3 14 6 h i o m 5 0 S - 6 7 ° 1 6 ! 5 Table I I cont'd L.M.C. F i e l d #9 S t a r R i g h t A s c e n s i o n (1975) D e c l i n a t i o n (1975) 1 5 h 45 m 19 S -71°35.2 2 5 h 45 m 24 s -70°38.2 3 .... 5 * 47 m 23 s -70°33!5 4 5 h 4 6 m 49 s - 71°13 l8 5 5 h 4 8 m 12 s -71°13 ! 0 6 5 h 48 m 6 s -70°58 l4 7 5 h 48* 54 s -71°42.'8 8 5 h 4 9 m 37 s - 71°39 l2 9 5 h 4 9* I s -70°46!o 10 5 h 49™ 13 s -7 0° 44 .'8 11 5 h 4 9* 55 S ' -7 0°52.'6 12 5 h 50 m 7 S - 70°59 l5 13 5 h 5 0 m 3 1 S -7 0°45l2 14 5 h 5 l m 45 S -72°30!7 15 5 h 5 2m 25 S - 7 2°2l ! 3 16 5 h 5 2* 30 S -7 0° 36 .'5 17 5 h 5 2* 4 1 s -71° 26.'5 18 5 h 53* 4 s - 7 1 ° 3 5!l 19 5 h 53* 22 S -71°37 ! 1 20 5 h 54 m 4 S - 70°25 l5 21 5 h 54 m 23 S -70°33 ! 3 22 5 h 54 m 18 S -71° 0.*5 23 5 h 5 6 m 21 S -70°48!o 24 6 h o m 18 S -71°11 \l 25 6 h . 7* 9 S Table II cont'd L.M.C. F i e l d #9 S t a r R i g h t A s c e n s i o n (1975) 26 6 h 5 m 4 0 S 27 6 h 6 m 3 1 S 28 6 h l l m I I s 29 6 h 1 2 m 4 8 S 30 6 h 1 3 m i o s 31 6 h 1 6 m 9 S 3 2 6 h 1 7 m 5 0 S 33 6 h 2 0 m 2 S 34 6 h 1 9 m 1 9 S 35 6 h 1 9 m 4 6 S 36 6 h 2 2 m 4 3 s D e c l i n a t i o n (1975) -71°21!9 -7 0°44*9 - 7 1 ° l o ! 9 -72° 3 ^ -72°lo!4 -71°44!2 - 7 1 ° 3 6 ! l -72°28 ! 6 - 71°16 l8 -71° 9 l6 -72°37 !o Table II cont'd L.M.C. F i e l d #20 h m , , s 23 S t a r R i g h t A s c e n s i o n (1975) D e c l i n a t i o n (1975) 1 5 h 57™ 24 s -73°52!4 2 6 9 14 -73°50.1 3 . 6 h 14 m 22 S -73°53ll 4 6 18 0 s -74° 1.3 Table II cont'd L.M.C. F i e l d #23 S t a r R i g h t A s c e n s i o n (1975) 1 6 h i o m 27 S 2 6 h l l m 38 s 3 6 h l l m 56 S 4 6 h 12 n 45 S 5 6 h 13 m 8 S 6 6 h 13 m 21 S 7 6 h 13 m 44 s 8 6 h 15 m 39 S 9 6 h m 16 18 s 10 6 h 16 m 55 s 11 6 h 17 m 38 s 12 6 h 16 m 52 s 13 6 h 16 m i o s 14 6 h 16 m 3 1 S 15 6 h 16 m 19 S 16 6 h 16* 3 5 S 17 6 h 17 m 7 S 18 6 h 18 m 14 s 19 6 h 19 m 21 s 20 6 h 19 m 26 S 21 6 h 19 m 24 S 22 6 h 2 0 m 15 S 23 6 h 2 l m 20 S 24 6 h 22 m o s D e c l i n a t i o n (1975) -68°27.6 -68° 5 !'3 -68° 3.7 -67°34 ! o -67°56!3 -67°49.'9 -67°28 !4 -67°28.9 -67°25 ! o -67°29 .'7 -67°26!4 -67°53 !o -68 0.5 o » -68 3.5 O I -68 9.1 -68° 9l4 -68°13 ! 2 -67°47 ! 8 -67°49!8 -67°49.8 -68°22!2 -68°27 ! 8 -68°20.7 o « -68 0.6 Table II cont'd L.M.C. F i e l d #23 S t a r R i g h t A s c e n s i o n (1975) D e c l i n a t i o n (1975) 25 6 h 2 2 m 1 0 s -67 °59l4 26 6 h 2 2 m 2 6 S o » -67 52.3 27 6 h m 23 3 1 s -68°35!9 28 6 h 2 3 m 48 s -68°57 ! o 2 9 6 h 2 5 m 5 5 S -68o10.'8 30 6 h 2 6 m 2 1 S -68°46.'8 ) 31 6 h 2 6 m 4 2 S -68°49.'2 32 6 h 2 7 m 16 S -68 °52!0 33 h 6 2 8 m 56 S -68 °54!6 34 6 h 3 l m 2 1 S o » -69 11.1 35 6 h 14 m 16 S -68°48!8 36 6 h l l m 3 7 S -68°52.'8 37 6 h l l m 5 7 S -68 °58\l 38 6 h 1 3 m 5 5 S -68 °58l7 39 6 h l l " s 54 -69°15.'l 40 6 h 1 3 m 24 S -69 °14 ! 4 41 " 6 h 1 2 m 2 1 s -69 °44 ! 6 42 6 h m 11 50 S -7 0° 1.'3 43 6 h 1 3 m 4 6 S -70 °13 ! 0 44 6 h 1 5 m 6 s -70 ° 0 ! 2 45 6* 15 m 15 S -70 °29 !3 46 6 h 24 m 4 7 S -70o13.'6 47 6 h 24 m 3 9 S -69°53l2 48 6 h 24 m 4 0 S - 6 9 ° 4 4 ! l 49 6 h 2 5 m 5 S - 6 9 °4 4 ! 0 50 6 h 2 9 m 3 S -70°20l4 51 6 h 13 m 3 8 s -69°28 !3 Table I I c o n t ' d L . M . C . F i e l d #24 S t a r R i g h t A s c e n s i o n ( 1 9 7 5 ) D e c l i n a t i o n ( 1 9 7 5 ) 1 6 h 2 6 m 4 7 S - 7 1 ° 4 1 . 8 h n . s 2 6 " 29 3 4 ° - 7 0 ° 5 5 . 5 3 6 h 3 0 m 4 2 s - 7 1 ° 0 . 6 .... ». . •„<"-* />'<•*•* ~ F i g . 1 Finding Charts LMC F i e l d #1 \ . * . " * * / . 0 I • . • T 7 •I .. . . . . Y . ^ : r . ' - .•.-» I S * . • • • v rig-"* •*•«-• F i g . 1 cont. LMC F i e l d #1 N3 00 29 . . . . • ... * •  r * it*-" *v% -r.-,* • ~ v"' •'" •••'4 y.yr^i.VVJ-'mrv, matt .v* f * sis y> * - - "v"*? V • • • •• ••• *v '•••• 5 , . ' • • s r . . ' - • . ! . • ' ' V. Si, %-»W4 / . . • • • * 4 •'•*••»• . v ' - ' * • • . .. . • - • %*.mz ". - -'it ' >••>:" •' »• , ;•• r.- < »t • • • j • , \ * s j " ' * * » • • ' . •••• ' V . 5 i ?» o 7*J?* - • • • * •'- »*:•> r H OJ •H U a 4J C o o •H F i g . 1 cont. LMC F i e l d / / l co o V F i g . 1 cont. LMC F i e l d #2 H .v F i g . 1 cont. LMC F i e l d #2 S3 !.\'-;- :> vti V •••• V ' - A .. .•'«."•"" '.''..•>-#,v̂ '- ••" v '.' . . • * • . . . • • '•*.•* v i • • * i : J • * • v • v. • • *< i • •. . - . . • • ... F i g 0 1 cont. LMC F i e l d #3 • - ft'.  u> F i g . 1 cont. LMC F i e l d //4 0 1 •j "~~ - *. . * • t • .* • . • • - . . • y '3 • 1 • • • f. , • •* • i '' • • ' V • ' " ^ B» • SI * ' * ! < . i • ... * • « • 1 Ms*. r 1 I I 16*. • © • k- I,. 1 • / F i g . 1 cont. LMC F i e l d #4 U) ON  F i g . 1 cont. LMC F i e l d #4 l»- Sr * • « - * • I ' r**» ••">•» 39 $4* fe . • . » • i -V ' ] •Bill rlJMiiTT Tin ' i i_mjj 5kV * ; . •'•>! iff"* 1 , >•< t k : ... . " •••• • ' • • • . * * * '• • * -7 =& H •H a o o to « • " • • a ' «.»,"» .A* : ' t -4 • • ., : • 't. i * - » . . . . 1 r • • • .. ^ • • • • . v • • % •. ***•. • •••• «i • , : • • • / • >, " h O ' ' " - • • '••••'•3 •>. •» v- * ; - •••V- • * '--ii •••• K ; i f : . trim . • V 4*.-.' . i.v. 1 • • . . t * * *• •.. . I N . pre • ' • • • k - * . Ax \ » «• ta ^ ft k s i * » 3».' •••• r.*^> -̂:;i:;<? B e ' •••••• • « *>r - J"- . • * V «,*t. * vasrWi?*J k*.*H>. i A . * . v *, . .f , JVC* •/<•• ^ * - » t - - F i g . 1 cont. LMC F i e l d #6 r.j>t. 0 * IL" • 7, • * . • <.,v-.... *4 *. o » » •».•* a) •rl a 4-> c o o to  F i g . 1 cont. LMC F i e l d #6 i '•* » f -'V-.. '*.- •••• • t m - yryv<w»'ai — , ^ » 1- T>1 • *. 1 • • •••• * • • • , iff Jf . e * ** * " ..• ° » » a . 7 * '•. ' .• • \ v ..... •• • ' *.i • .. •; . •' ' •• • , • -. :': • . - » * i • ; • . " 6 . . ' . •V. .«v • F i g . 1 cont. LMC F i e l d #6 : y I • • J / / v .1 47 i r . • : • . • #<:\ '•*.•: » / • ' • ' " > ' .* v " v' L i » ? ' \>"J* .» . * ' % • • . • ; ' • L •*- f • . ' • • ' ' t - . * * • : :*f u- •: . y - ... : . \ - r- .-••»•*, c. - * * ••*...•• . » •. >v:, « . . . • .'*v.. •  * * «, 1 » • * V ' • •A W . 1 • ... •' .»>.. . ".• •H fe CJ 2 i-l 4 J o a 6.0 • H P H ;..v:.--.....".v..^ .v i •••'••Lr'.*'Tv .• • . . « • > • *• .. • • ' :-ml * WD .<"••>:••v•:v>1 . - *.^**YYY Y ' ^ Y Y / * Y •V*" , M ' • . ». . . • Y , S 7 Y ' 4 v A. •Y.̂ >* ' i , - T - : ; > ;>•:• ,v%V*<i •» , c . « 8 . Y • • q '. Y .-V V\ V- . Y . ' - ' V Y . v...f V V " . V ^ : »A.- Y - ' : i . Y # Y - : j Y . : - v \ - r - : - Y Y *• ^ •4 tSUkj. i.4liJ<! < Y ; Y F i g . 1 cont. LMC F i e l d #6 0(9 49 '•- *» V • •• * , * " ?•>. * 5 * * V * z*<v " -' • - * M • . V •' • • ' i . . - v . : - . v F z -'' • * • i . " • • * ••. % i » ? • ' * ... • . * : jr.. * • •t • * * "• • • ' i ; * . f ; - ...» •>•• *;/^f3 t • „ • • i r v •;.•< a 9 ^ h ' i v ^ . < y •,.r>-.-:; ' V . • . :J>i-.;--;...;•>;/< r- ' K V - v. • - i . - . . * fey ; * c ; v ^ V ; r -X.. .1 • I/* a. - • X . ' • - * , . . - . p ••••• ' . •. ' '"• : V v I .... KM '•• •*-*;/ 'Ki '*-•' « • " F i e . 1 cont. LMC F i e l d #6 o i F i g . 1 cont. LMC F i e l d #7  F i g . 1 cont. LMC F i e l d #8 * I'.' « . . . / • • A • • • » « •y * , ' . . .1."! ••' • " . • . ' ! ' • ' » • . - ' • fa*- ' ' ,•• '•V-' • • .V- ••• ..V I Y/:'->:'-' 2- £>\ ••'•'.*'.':-v3 f * i > ' • - t . : . . . . • 5. V * Y. = t V':' • • • > . 1 v : W-TV: "-."..rrv ,;v3v. F i g . 1 cont. LMC F i e l d #9      i F i g . 1 cont. LMC F i e l d #23    64 • Y.-« •.•vi •• • • i E t * * f. - * • '• •: Y •.. • j ft- ;* : , - -• v 1 ^ " * ' Y : •••'•;̂ Ŷ -T!\>.!̂ gwiw»̂ I- • • t~K-:, w% i • ,* r r i - fe'*- • • ' * ' M - * f l " • * *) p ' •"5* • Y . • Y •Y4 • ••Y fv; - Y | • .:* 1 • it * k " ' | • • • Witt* j ' • ' '' * " . * J Vio. 1 r n n t . T.MH F i e l d #24 S 66 I i i £]l££2J§££ic Observations The a b s o l u t e magnitudes of carbon s t a r s are very poorly known. No carbon s t a r i s near enough to have a r e l i a b l e t r i g o n o m e t r i c p a r a l l a x , carbon s t a r s are r a r e l y members of b i n a r y systems and they are seldom found i n c l u s t e r s . A l l the forementioned f a c t s make i t d i f f i c u l t to o b t a i n a b s o l u t e v i s u a l magnitudes - f o r these o b j e c t s . However the Large M a g e l l a n i c Cloud i s near enough and i t s d i s t a n c e i s w e l l enough known so t h a t the a b s o l u t e magnitudes o f carbon s t a r s i n the Large M a g e l l a n i c Cloud can be a c c u r a t e l y determined. To t h i s end p h o t o e l e c t r i c measurements of f o r t y of the s t a r s i n the c a t a l o g u e have been obtained on the VRI system. The VRI photometry was obtained with the one metre t e l e s c o p e on Cerro T o l c l o on the n i g h t s of Dec. 17-22 1974. Table I I I c o n t a i n s the photometric data f o r a l l the s t a r s which were observed along with comments f o r some of the s t a r s . For two of the s t a r s only the R-I c o l o u r was obtained and f o r one other s t a r only V and V-R was obtained. The s t a r s f o r which s p e c t r a were taken w i l l be d i s c u s s e d i n S e c t i o n IV. The photometry was c a l i b r a t e d on each n i g h t using an average of seven standard s t a r s , and e x t i n c t i o n c o e f f i c i e n t s were c a l c u l a t e d f o r each n i g h t . The average e x t i n c t i o n c o e f f i c i e n t s f o r the t h r e e n i g h t s were: KM=0.111, K (V-R) =0. 024, K (S-1) =0.088. These average e x t i n c t i o n c o e f f i c i e n t s agree very w e l l with those obtained i n p r e v i o u s observing runs(Olson, p r i v a t e communication). The average rms d e v i a t i o n f o r the standard 6 7 Table I I I Carbon s t a r photometry STAR V V-R V-I COMMENTS 1-1 16.34 2.53 3.49 1-2 16.06 1.87 3.36 1-4 16.35 2.77 4.16 1-5 14.20 0.43 1.72 Not a carbon star 1-9 15.68 2.19 3.42 1-10 15.42 2.15 3.50 1-11 R-I 1.25 • 1-12 13.87 1.14 2.00 Spectrum obtained 1-13 16.09 1.92 3.16 1-14 15.71 2.28 3.49 1-16 14.72 0.28 0.39 Not a carbon star; spectrum 1-18 15.86 1.88 2.71 1-20 15.57 2.12 3.33 Spectrum obtained 1-21 ' 16.18 2.23 3.68 1-22 16.17 2.24 3.34 1-23' 16.08 2.42 3.72 4-1 15.84 1.80 3.05 4-2 _15.74 2.17 3.46 4-3 16.69 2.74 4.12 4-5 15.99 2.17 3.53 4-6 16.80 2.62 4.16 Perhaps i n a nebula? 4-9 15.77. 2.03 3.49 Spectrum obtained 4-10 16.02 2.31 3.74 6-1 16.09 2.82 4.24 6-2 15.70 2.03 3.38 6-3 R-I = 1.56 6-4 15.29 2.07 3.29 Spectrum obtained 6-5 15.53 1.78 3.04 6-6 14.27 1.33 2.32 Spectrum obtained 6-9 15.47 2.17 • 3.34 6 8 Table I I I cont'd STAR V V-R V-I COMMENTS 6-10 15.69 2.03 3.36 6-13 15.73 1.86 3.03 6-14 15.61 1.90 3.14 6-15 16.30 0.39 Not a carbon star; probably wrong star indicated on chart 6-16 14.94 1.67 2.90 6-17 15.35 1.91 3.16 Perhaps i n a nebula? 6-18 15.91 2.33 3.72 6-19 15.65 2.37 3.67 6-20 15.84 3.05 4.37 6-21 15.48 2.27 3.57 6-22 15.39 2.06 . 3.17 Spectrum obtained 6-23 16.45 0.54 2.21 Not a carbon star 6-24 15.49 2.09 3.37 Close companion 6" north 6-25 15.47 1.85 3.10 Spectrum obtained 6-26' 15.84 2.34 3.57 6-27 15.20 0.69 1.88 Not a carbon star 6-28 16.01 1.97 3.27 69 stars was 0.04 magnitudes in V and about 0.03 magnitudes for both of the colours. With t h i s ' sample of f o r t y carbon stars for which the absolute v i s u a l magnitude i s known to a f a i r degree of accuracy, a r e l a t i o n s h i p between absolute magnitude and various parameters can be investigated. However one must remember that we are working with a r e s t r i c t e d sample of stars, i n the sense that these forty stars are on the average brighter than the average carbon star i n the Large Magellanic Cloud. This arises from the fact that only a one metre telescope was used to make the observations. This r e s t r i c t e d the observations to the brighter members of the catalogue. The brightest carbon star observed in the v i s u a l region has an apparent vis u a l magnitude of 13.87 while the f a i n t e s t has a magnitude of 16.80. If one assumes a distance modulus to the Large Magellanic Cloud of 18.5 (westerlund 1972) the absolute vi s u a l magnitudes are -4.6 and -1.7 respectively. Fig. 2 i s a plot of apparent v i s u a l magnitude versus the photometric colour, S-I. It can be seen that in general the f a i n t e r stars are also the redder stars, although the scatter around the mean l i n e i s guite large. One star, marked by the hourglass symbol seems to be discordant with the r e s t of the sample. It i s possible that t h i s star i s net a carbon star but some other type of red giant. The two stars marked by diamonds are separated from the bulk of the stars by about 0.3 magnitudes i n (B-I), These two stars are carbon stars as spectra were Figure 2. V versus R-I A A A A X A A A A A A A A A A A _ \ A ^ A A A A A z ^ A A A A A <!> A 0 D.B 1.0 1.2 1.4 R-I 71 CD 10 L O . Figure 3. V versus V-I A A A A rv L O . CO i n —1 i n i n . LCI -a". c a r n 1 .B 2.25 A A A , A 1 A A A A A A A A A & ^ A A 2.7 3.15 V-I "1 3.6 A 4.05 4.5 Figure A. V versus V-R 73 obtained of both of these. However such warm bright carbon stars are not known i n our Galaxy. It i s possible that they are high l a t i t u d e CH-stars although the red spectra ava i l a b l e do not allow a d i s t i n c t i o n to be made between late type carbon stars and CH-stars. In t h i s case blue spectra would be needed to ve r i f y t h i s p o s s i b i l i t y . If these stars were CH-stars then the spectra would be expected to show enhancement of the G -band as and 4 are the same type of plots as in Fig. 2 only now the independent variable has been changed to (V-I) and (V-R) respectively. The same symbols have been used for the stars mentioned i n F i g . 2. - In these l a t t e r two diagrams the relationship between magnitude and colour i s not as t i g h t as in the V versus (R-I) diagram* From these three diagrams i t does not appear that any tight c orrelation can be found between vi s u a l magnitude and photometric colour index for the red and near in f r a - r e d colours. Figure 5 shows a plot of absolute bolometric magnitude versus (V-R) • for the carbon stars i n t h i s sample. The bolometric corrections used were those found by Olson and Richer (1975) i n t h e i r investigation of the correlation between bolometric correction and photometric colour. The s o l i d l i n e s represent the mean location of the Ib supergiant branch and the class III giant branch. The carbon stars in t h i s sample seem to form quite a d e f i n i t e branch between the Ib supergiants and the normal giants. However t h i s appearance may be somewhat a r t i f i c i a l as the sample of carbon stars i s somewhat brighter well as enhancement Figures 3  75 than average, as l e a s t in the v i to say that the cool carbon st bright giants to ordinary g i magnitude. s i b l e region. I t would be safe ars seem to cover the range from ants i n absolute bolometric 76 I V S£ectrosco£ic Observations Carbon stars'exhibit one of the most complex spectra of any astronomical object i n the v i s i b l e and near infrared regions. This spectral region contains a multitude of atomic l i n e s as well as the absorption bands of such molecules as 1 2Ci*N, 1 2C l 2C,* 2CH and the other isotopes of these species. The complexity of t h e i r spectra has always hampered attempts to interpret t h e i r spectra i n terms of temperature, luminosity and abundance e f f e c t s . Any attempts to correlate luminosity and spectral features have been hindered by the lack of good absolute magnitudes for a s u f f i c i e n t number of carbon stars and because of d i f f e r i n g abundances. There'are just not enough absolute magnitudes of s u f f i c i e n t accuracy known to determine the luminosity from the spectrum of any given carbon star. This of course assumes that i t i s possible to do this for carbon stars as i t i s for most other stars. Since the :carbon stars i n the Large Magellanic Cloud are r e l a t i v e l y f a i n t a large telescope i s needed to get good s l i t spectra of a "large sample of these stars to investigate luminosity e f f e c t s . The main purpose of my spectroscopic investigation was to confirm that the objects were indeed carbon stars, by observing molecular i 2 c * 2 C bands, and to note some of the grosser features in the spectra. S l i t spectra at a dispersion of 117 AVmm were obtained with the image tube spectrograph of the 1.5 meter telescope at Cerro 77 Figure 6(a) Carbon s t a r spectra, region 1 Figure 6(b) Carbon star spectra, region 2 79 Tololo i n December 1974. The phosphor of the image tube allowed the use of baked Ha-0 plates to greatly increase the speed of the system.- In general the spectral range covered was from 5000A-8000A. The faintness of the objects dictated exposures on the order of one hundred minutes. The d e t a i l s of the observations are found in table IV. On such long exposures with an image tube the number of ion events becomes s i g n i f i c a n t and hence the background fog l e v e l becomes quite high. Table IV Spectroscopic Observations I | Star I J 1-12 | 6-25 | 1-20 I 6-6 | 6-22 | 4-9 | 6-4' E.A. (1975) Dec.(1975) 5 03 11 |-66 0 2 . 9 | Dec. 14/74 J 91 m i n . 5 39 19 | - 7 2 1 0 . 4 I Dec.14/74 | 85 1 1 5 00 26 1-65 0 2 . 5 JDec.15/74 |118 »• 5 05 06 1-70 2 7 . 6 |Dec.15/74 J 92 " 5 38 00 1-70 4 9 . 1 |Dec.16/74 i 123 » 5 17 10 |-64 4 8 . 5 | Dec. 16/74 |91 " 5 02 04 |-70 5 3 . 3 |Dec.16/74 |10 4 »• Date (U.T.) Exp. Time Spectra of eight stars were obtained and only one of these(star 1—16) was not a carbon star. The other seven stars showed molecular bands of C^as well as bands of CN. The stars showed a great-range in the strength of the molecular bands as well as i n the strength of the D-lines of sodium. None showed Hc^in absorption and only one showed a trace of emission at H«=»< . 80 Emission at H"°^ i s t y p i c a l of the carbon Long Period V a r i a b l e s . In g e n e r a l the only atomic l i n e s seen were the D - l i n e s and H°<. T r a c i n g s of the s p e c t r a over the wavelength i n t e r v a l 850-6950A are shown i n F i g u r e 6 (a) while F i g u r e 6(b) shows the i n t e r v a l from ^5000 to ^5900. These t r a c i n g s were produced by d i g i t i z i n g the s p e c t r a at 5/c i n t e r v a l s on the J o y c e - l o e b l • M i c r o d e n s i t o m e t e r of the Geophysics and Astronomy Department at OBC. The r e s u l t i n g data was smoothed with a nine- p o i n t t r i a n g u l a r f i l t e r to reduce the n o i s e . For comparison, two G a l a c t i c carbon s t a r s were a l s o reduced in the same manner. The Large M a g e l l a n i c ' Cloud has a systematic v e l o c i t y r e l a t i v e to the sun of about 250 kmsec - 1. Almost a l l o f t h i s i s due to s o l a r motion. T h i s enables one to a s c e r t a i n whether a s t a r i s a probable member of the Cloud or not j u s t by measuring the r a d i a l v e l o c i t y of the s t a r . S e v e r a l s p e c t r a of G a l a c t i c carbon s t a r s were obtained each n i g h t to serve as r a d i a l v e l o c i t y standards and s i n c e the only atomic l i n e s d e f i n i t e l y present i n the Large M a g e l l a n i c Cloud s t a r s were the D - l i n e s of sodium, I had to r e l y on the p o s i t i o n of the molecular band heads f o r r a d i a l v e l o c i t y measurements. T h i s procedure ad m i t t e d l y i n t r o d u c e s more e r r o r i n t o the v e l o c i t y measurements but the r e s u l t should s t i l l i n d i c a t e whether or not the s t a r i s a • member of the Large M a g e l l a n i c Cloud. The wavelengths of s e v e r a l band heads i n the G a l a c t i c carbon s t a r s were measured and : a f t e r c o r r e c t i n g f o r the motion of the earth a set of standard wavelengths was produced. The p o s i t i o n s of the 81 corresponding band heads in the Large Magellanxc Cloud carbon stars were'then measured r e l a t i v e to t h i s set of standard wavelengths. The f i n a l r a d i a l v e l o c i t y was found after correcting for the earth's motion i n the direction of the Large Magellanic 'Cloud; The r e s u l t s are shown in Table V along with other pertinent quantities for the seven stars. Ihe number i n parentheses i s the probable error in the r a d i a l v e l o c i t y . The average velocity of 245 kmsec - 1 i s in excellent agreement with the systematic v e l o c i t y of the Large Magellanic Cloud found by Bok ( 1 9 6 6 ) . Table V-groEertj.es of the Seven Carbon Stars ir | Star T — | Vr (kmsec-*) i „_ , . H 1 v — r | V-R ~|— | V-I "T T " 1 Mv | Mbol i ! j ! J | 1-12 1 344 (17) j 1 3 . 8 7 |1 .14 I2 .00 1-4.61 - 5 . 7 | 6 -6 | 3 4 6 ( 6 6 ) J 1 4 . 2 7 I 1.33 J 2 . 3 2 j - 4 . 2 1 - 6 . 0 I 6 - 4 I 198 (50) |15 .29 | 2. 07 |3. 29 1 - 3 . 2 | - 6 . 6 1 6 - 2 2 | 189 (34) 115 .39 | 2 . 06 J 3 . 1 7 J - 3 . 1 | - 6 . 5 1 6 -2 5 | 198 (43) 115 .47 j 1. 85 |3. 10 l -3.0 1 - 5 . 8 | 1-20 i 190 (38) | 1 5 . 57 I 2. 12 I 3 . 3 3 1-2.91 - 6 . 5 |4-9 j 253 (17) | 1 5 . 7 7 j 2. 03 13. 49 1 - 2 . 7 | -6. 0 L .„ i,. X j . _ -. j . • i i The tracings in- Figure 6 show the carbon star c h a r a c t e r i s t i c s of the program stars quite well, p a r i c u l a r l y Figure 6 (b). Prominent features are marked on the tracings. Night sky l i n e s are indicated by n.s. while plate flaws are 82 marked by a dot. Table VI g i v e s the C - c l a s s i s i c a t i o n as d e f i n e d by Yamashita(1972) f o r each s t a r together with an i n t e n s i t y measure f o r each s p e c i f i c l i n e or band on Yamashita's s c a l e . These i n t e n s i t i e s were determined by comparing the Large Ma g e l l a n i c Cloud carbon s t a r s with the G a l a c t i c ones. (D= Na D- l i n e s ; C A = i 2 C i z C bands at XA5636,6T91; 13=i*Ci3C b ^ n d at X 6 1 6 8 and i 3 C i 4 N band at )*6260; CN="Ci*N band at X5730 and ^6206; L i - L i t h i u mI 6708 ; H«< — X6563) A d i s c u s s i o n of the spectrum of each i n d i v i d u a l s t a r f o l l o w s . Table VI C l a s s i f i c a t i o n of Carbon Stars Star 1-12 6-6 6-4 6-22 6-25 1-20 4-9 C-type C4,2J C4,4J C6,3 C6,4 C4,4 C4f 5 C 4,4J D ] Cz I j 4+ j 2 4 | 4 6 i .3+ 6 | 4 3+ | 4 3+ | 5 2 | 4 13 4 + 4+ 3 + 3 3 3 5+ CN 2 3 3+ 3 3 3 + 3 L i 0 0 0 0+ 0 0 0 0 0 e? 0 0 0 0 1-12 - This s t a r was the b l u e s t and b r i g h t e s t ( i n V) of any of the s t a r s observed. I t shows moderate J - s t a r c h a r a c t e r i s t i c s as d e f i n e d by Bouigue(1954) and Gordon (1967) with the i 3 C i * N (4,0) band at )\6260 83 s l i g h t l y s t r o n g e r than the corresponding 1 2C l+N band at )i6206. The (0,0) band of i 2C"C i s of moderate s t r e n g t h but the (0,1) band i s s u p r i s i n g l y weak. The (0,2) band of i 2ci 2C i s b a r e l y v i s i b l e while the (1,3) and (2,4) bands are present but weak. The Sodium D- l i n e s are present with seme s t r e n g t h but L i \6708 and H<*> are d e f i n i t e l y not present a t the r e s o l u t i o n used. 6-6 - This s t a r was the next b l u e s t one observed as w e l l as being the second b r i g h t e s t v i s u a l l y . The (0,0) and (0,1) bands of 1 Z C 1 2 C are moderately strong and are very w e l l d e f i n e d . The +2 sequence of 12C12C, (0,2) , (1,3) , and (2,4) , i s present but weak. The wavelengths o f these f e a t u r e s are ^6191, \ 6122,and ^6060 r e s p e c t i v e l y . The * 2c*3C band at X6168 i s present with c o n s i d e r a b l e s t r e n g t h as i s the l 3C 1*N(4,0) band a t ^6260, i m p l y i n g a r e l a t i v e l y high abundance of * 3C. Although the spectrum i s somewhat weakly" exposed shortward of W 5000 A th e r e i s an i n d i c a t i o n t h a t the M e r r i l l - S a n f o r d band(probably SiC j J i s present a t ^ 4977 . The sodium D - l i n e s are q u i t e s t r o n g but they are not r e s o l v e d . There i s no t r a c e of e i t h e r H or Li/\6708. 6-4 - In the spectrum of t h i s s t a r the IZQIZQ (0,1) and (0,0) bands are weak to moderate i n s t r e n g t h while the 84 (1,3) and (2,4) band heads are much stronger. There i s a weak trace of i z c 1 3 C at ^6168 and the region from ^6260 to ^ 6285 seems to be depressed s l i g h t l y implying a somewhat higher than normal abundance of l 3C. The l 2C J*N bands are present with moderate strength although the (4,0) and (6,2) band heads appear to be strongly enhanced. Weak emission may be present at . 6-22 - The 1 2C 1 2C(0,0) and (0,1) bands are of moderate strength and are quite well defined i n th i s s t a r . The 1 2G 1 4N bands are well developed and saem to be of average strength. The two* Na D-lines are resolved and appear to be of moderate strength. The L i ^6708 l i n e appears to be present with considerable strength along with the KI l i n e at ^7699. There i s also a band, degraded to the red, with the band head at about ^ 6380. This band also appears in the spectrum of wz Cas, a peculiar Galactic carbon star, but remains unidentified (Catchpole 1S75). The i£C* 2C bands are stronger i n 6-22 than in WZ Cas while the Na D-lines are weaker.'• The abundance of * 3C in t h i s star appears to be normal. 6-25 - The sodium D-lines are present but weaK. while most of the i 2 c l 2 C bands appear to be of moderate strength. 85 The abundance of 1 3C seems to be normal as the l 2 C i 3 C band i s present but very weak and the ̂ c 1 4!) band at V)S6260 i s not at a l l v i s i b l e . . Neither L i ̂ 6708 nor He* are present. 1-20 - A l l the 1 ZC> 2C bands i n t h i s star are very well developed. The +2 seguence i s especially strong. The abundance of l 3C appears to be normal as the i 3 c 1 * N band at ^6260 i s not v i s i b l e while ^6168, *zcl3C, i s v i s i b l e but weak. The sodium D-lines are of moderate strength and there i s no trace of L i ̂ 6 708 or JP< . 4-9 - This star shows an extremely high abundance of 1 3 C as displayed by the strength of the i 2 C 1 3 C and l 3C l*M bands. The most outstanding feature in the entire spectrum of 4-9 i s the(4,0) band of i 3 c 1 * N at X 6260. The 1 corresponding I 2 Q I 4 J J a t X 6206 i s present but weak. The l 2 C l 2 C band at ^5636 i s very strong but the i 2 C 1 2 C band at X&191 i s actually weaker than the corresponding i 2 c 1 3 C band at ^6168. There may be two i 3cn 3C bands present, the (1,3) band at "X6080 and the (0,2) band at)\6145. The Na D-lines are weak but t h i s should ,be considered i n l i g h t of the fact that the entire region frcm ^\5750 to ^6150 i s depressed due to absorption from i 2 c l 3 G and i 3 c l 3 C as i s the case for the more extreme Galactic J stars (Yamashita 1972). 86 It i s also possible that t h i s star shows a weak KI l i n e at ^7699. A l l of the stars above display molecular bands of C j , . It i s perhaps s i g n i f i c a n t that three of the seven show higher than normal abundances of •• 1 3G. This i s proportionally more stars than for Galactic carbon stars. It i s also suprising that none of the stars show d e f i n i t e H~- emission, which i s c h a r a c t e r i s t i c of the Long Period Variables. I t i s possible that the two bluest carbon stars(1-12 and 6- 6) are not members- of the Large Magellanic Cloud but are actually high l a t i t u d e CH s t a r s . These stars are mildly peculiar spectroscopically and bear some resemblance to the CH stars found in OJCentauri by Dickens(1972). In the following section I w i l l assume that a l l seven are members of the Large Magellanic Cloud. 87 I Carbon Stars i n the H-R Diagram The precise evolutionary phase (or phases) of caroon stars i s not presently understood. They are believed to be highly evolved objects which are exhibiting the products of nucleosynthesis i n t h e i r spectra. Besides determining t h e i r evolutionary status from data on masses, ages, spectra, and atmospheric abundances, one would l i k e to know th e i r p o sition i n the H-E diagram. The H-R diagram has been very useful for comparing theoretical- models with observations in order to determine an object's evolutionary status. In order to place an object i n the th e o r e t i c a l H-R diagram i t i s necessary to know the absolute bolometric magnitude as well as the e f f e c t i v e temperature of the object. F i r s t I w i l l address myself to the problem of finding the absolute bolometric magnitude of a cool carbon star. One can find the bolometric magnitude of an object by integrating the observed energy d i s t r i b u t i o n over a l l frequencies to find the t o t a l energy emitted by the' object. However t h i s can only be done f o r the brighter objects; Mendoza and Johnson (1965) have done t h i s f or a few dozen Galactic carbon stars, with photometric observations extending f a r out into the infrared where most of the carbon star's radiation i s emitted. It i s fortunate that t h e i r r e s u l t s show a good c o r r e l a t i o n between the calculated bolometric correction - and the (V-R) colour index for both R and N stars. Olson and Richer(1975) have investigated this c o r r e l a t i o n and fi n d the relationship shown i n Figure 7. There are two 88 Figure 7. Bolometric c o r r e c t i o n s • N - s t a r © R - s l a r •~5> ? y / / 0/ e / / o / © s V - R 2 89 d i f f e r e n t r e l a t i o n s shown; one for the R stars and one for the S stars. Since the R stars are much fainter(absolutely) than the N stars i t i s expected that a l l the carbon stars observed i n the Large- Magellanic Cloud are N-type carbon stars. Therefore the bolometric corrections for N stars were used. In a few cases where the stars were s l i g h t l y bluer in (V-B) than the bluest Galactic. N star- used i n the c a l i b r a t i o n the bolometric correction was calculated by simply extending the l i n e a r portion of the c a l i b r a t i o n curve for N stars to fi n d the correct value. It i s expected that the bolometric corrections are good to about 0.3 magnitudes. I have neglected i n t e r s t e l l a r reddening i n obtaining the absolute bolometric magnitude for these stars for two reasons. F i r s t , there i s very l i t t l e reddening i n the dir e c t i o n of the Large Magellanic Cloud (Bok and Bok 1972). Second, any reddening which i s present w i l l tend to move the stars along the c a l i b r a t i o n curves rather than across them. This i s because'the reddening w i l l cause the star to appear f a i n t e r v i s u a l l y but i t w i l l also increase the bolometric correction, hence the two effects tend to cancel out. The problem of assigning e f f e c t i v e temperatures to the cool carbon stars i s not as e a s i l y resolved as the question of bolometric' corrections. F i r s t , there are only two N stars for which r a d i i have been measured by the method of lunar occultation. Further, no N star i s a known member of an ec l i p s i n g binary system so that the radius may not be determined by t h i s method. It i s not possible to use the c a l i b r a t i o n based on various photometric colours set up f o r M giants as the 90 sources of opacity are- quite d i f f e r e n t for the carbon and H giants. In fa c t the l a t e type carbon stars radiate more nearly l i k e black bodies than do M stars (Bahng 1966 ; Barnes 1973; Bessell and Youngbom 1972). Scalo (1976) 'has- investigated the consistency of using blackbody temperatures for carbon stars as opposed to using temperatures derived frcm an M star c a l i b r a t i o n . He has derived blackbody colour temperatures frcm the' (R-I) , {(R+I)- (J+K)) , (I- K), and (in most cases) the (I-L) colours for twenty-three stars from the available photometry(Mendoza 1967; Lee 1970; Eggen 1972a). He finds the t y p i c a l t o t a l spread i n derived blackbody temperature i s only 50-200°K. The requirement that the blackbody temperatures be consistent i s a necessary requirement for t h e i r use -as e f f e c t i v e temperatures but i t i s not s u f f i c i e n t . Thus i t - i s possible to get a blackbody temperature from only one'colour'measurement, say (R-I), and be reasonably sure that the other colour indices would not give s i g n i f i c a n t l y d i f f e r e n t r e s u l t s . Bartholdi et a l . (1972) have measured an occultation angular diameter for the N s t a r , XCnc. Using Mendoza's(1967) r e l a t i o n between Te and-bolometric correction to eliminate the bolometric correction, they f i n d a Te of about 2500°K. However, aendoza's (I-L)' temperatures are probably too small. I f one uses the bolometric correction derived from the (V-R) colour index a Te of about 26400K i s obtained for a f u l l y darkened disk or 2810QK for a uniformly illuminated one. Various authors have measured 91 o c c u l t a t i o n diameters f o r 19 Psc(Lasker e t a i 1973; De Vegt 1974) and analysed them f o r e f f e c t i v e temperatures. Scalo(1976) adopts a temperature of 3050±2000K f o r 19 Psc and 27QO±100°K f o r X Cnc a f t e r c o n s i d e r i n g a l l the d e r i v e d v a l u e s . F i g u r e 8 shows a p l o t of c o l o u r temperature as a f u n c t i o n of (R-I). The f i l l e d c i r c l e s are the c a l i b r a t i o n o f G and M g i a n t s by Johnson (1966) while the open c i r c l e s are the c a l i b r a t i o n of M g i a n t s given by Lee (1970). The open squares are the c a l i b r a t i o n of & s u p e r g i a n t s by Lee(1970) and the c r o s s e s r e p r e s e n t the c a l i b r a t i o n of l a t e type Miras by Mendoza(1967). The s o l i d l i n e r e p r e s e n t s the blackbody r e l a t i o n while the f i l l e d t r i a n g l e s are the approximate p o s i t i o n s of the two carbon s t a r s f o r which angular diameters have been measured. Note how the two carbon s t a r s f a l l c l o s e r to the blackbody l i n e than to the H g i a n t c a l i b r a t i o n . T herefore i t seems reasonable to use blackbody temperatures d e r i v e d from the (R-I) c o l o u r index. In order to help understand the carbon s t a r ' s place i n s t e l l a r e v o l u t i o n i t i s convenient to place them i n a t h e o r e t i c a l H-R diagram. Figure 9 i s such a diagram. The f o r t y s t a r s f o r which photometry has been obtained are p l o t t e d . The e f f e c t i v e temperatures used were those d e r i v e d from a blackbody curve f i t t e d t o the (R~I) c o l o u r while the bolometric c o r r e c t i o n used was that of Olson and Richer (1975) from (V-R) photometry The t h e o r e t i c a l e v o l u t i o n a r y t r a c k s shown have been adopted from Scale (1976) and Scalo,Despain and Ulrich(1975) and r e f e r e n c e s Figure 8. Colour temperature versus R-  94 cited therein. A l l these models represent stars of disk composition, The thinner l i n e s correspond to the f i r s t ascent of the giant branch to core helium burning, as well as double s h e l l source models. The double s h e l l source models are the ones ly i n g to the r i g h t of the diagram. The thick l i n e represents the locus of'points at which the f i r s t helium s h e l l f l a s h occurs according to Schwarzscild and Harm(1965) for the 1M© model and Paczynski (1970) "and Iben (1972) for the larger masses. Models to the right of t h i s l i n e have two active burning she l l s and are undergoing thermal pulses in the helium s h e l l at f a i r l y regular i n t e r v a l s . The broken l i n e corresponds to the mean position of supergiants of luminosity c l a s s lab. The seven stars'from'Table V f o r which-spectra were obtained are i d e n t i f i e d by a number beside the corresponding point. This number corresponds to the star's position in Table V. Thus,for example, 1=1-12, 2=6-6, 7=4-9 etc. U l r i c h and Scalo(1976) esitimate that the uncertainties i n the temperatures of the double s h e l l source tracks due to possible errors i n convection theory and in the atmospheric opacities i s - no more than ±2000R. Scalo(1976) estimates that the uncertainty i n - the 'temperatures adopted from the (R-I) colour to be about 300°K. These uncertainties, along with the eff e c t of composition changes(Scalo and Dlrich 1975) make i t dangerous to' assign a mass sol e l y from the position i n the H-R diagram. Therefore the tracks are labeled mainly for ease of reference although I w i l l be assuming that the stars do have the masses assigned to them. 95 The f i r s t conclusion to be drawn from Figure 9 i s that a l l the stars observed appear to be in the double s h e l l source phase of'evolution. This i s in disagreement with the suggestion of Eggen(1972b) that the N stars are i n the core helium i g n i t i o n phase. In the double-shell source phase a star consists of a carbon-oxygen core •surrounded by a helium burning s h e l l and s t i l l further out l i e s the hydrogen burning s h e l l . Above t h i s l i e s the outer convective envelope of the star. The two warmest stars i n t h i s sample l i e f a i r l y close to the t i p of the 9 M<s> f i r s t giant branch so that i t i s not clear that tnese are double s h e l l source stars as opposed to core helium i g n i t i o n stars. However for the remaining discussion I w i l l assume that they are i n f a c t double s h e l l source stars. The next"thing to note from t h i s diagram i s the f a c t that, except f o r the f i v e stars -lying to the l e f t of the 7 track a l l the stars* are bounded on the lower l e f t by the onset of helium s h e l l flashes* -No cool carbon star less massive than 7 M© i s found in-the pre-helium s h e l l f l a s h phase of evolution. This strongly suggests that stars less massive than 7 II <g become cool carbon stars 'because of the onset of helium s h e l l flashes. For stars more-massive than 7 MQ t h i s fact i s uncertain as no models have been constructed which are evolved to the stage of helium s h e l l flashes. These stars could very well be post- helium s h e l l f l a s h objects as well. The exact mechanism by which the carbon i s mixed to the 96 surface af t e r the onset of the helium s h e l l f l ashes i s uncertain. Several d i f f e r e n t mechanisms have been suggested (Olrich and Scalo 1972; Scalo and U l r i c h 1973; Ul r i c h 1973; Smith,Sackmann,and Despain 1973; Sackmann,Smith and Despain 1974; Iben 1975,1976). The basic idea i s to bring hydrogen, carbon and helium into contact at high temperatures. It i s possible that the i n d i v i d u a l mechanisms work more e f f i c i e n t l y f o r certain mass ranges than for others. There e x i s t s an almost unique core mass-luminosity re l a t i o n s h i p for double s h e l l source red giants (Paczynski 1971; Iben 1976). Knowing the absolute bolometric magnitude of a double s h e l l source star allows one to assign a mass to the core, assuming that the core i s non-rotating. It i s i n t e r e s t i n g to calculate the core mass of the most luminous(bolometrically) star in t h i s .sample. Using Iben's r e l a t i o n s h i p , L/LQ = 6x10* (Mcore - 0.41) one find s a core mass of 1.73 . This i s well above the Chandrasekhar l i m i t i n g mass { 1.4M<9 ) which i s the maximum mass for such a carbon-oxygen configuration. The spectra of stars 1- 12 and 6-6 indicate that s i g n i f i c a n t mixing has already occured in these stars. Since they are both above the t h e o r e t i c a l upper mass l i m i t for the core f l a s h ( 2.3MQ ) and i f they are pre- helium s h e l l f l a s h objects t h i s implies that the "hot-bottom" convective envelope hypothesis of Sealo,Despain, and Ulr i c h (1975) may be responsible f o r the mixing observed in these stars. These stars are well above the c r i t c a l luminosity for 97 t h i s e f f e c t to occur. It i s also worthwhile to comment on the very i n t e r e s t i n g star 4-9, number seven i n Fiqure 9. This star e x h i b i t s an extremely high abundance of 1 3 C so that i t i s presumably the most highly evolved object in t h i s sample of seven stars i n the sense that s h e l l flashes have been occuring in t h i s object for a s i g n i f i c a n t period of time. As the temperature at the base of the convective envelope increases i t becomes easier f o r 1 2C to form l 3C and 1 4N by single and double proton captures respectively. If the temperature at the base of the convective envelope keeps r i s i n g i t i s possible that 4-9 could ba on i t s way to destroying i t s carbon s t a r c h a r a c t e r i s t i c s . 98 VI Summary In t h i s t h e s i s a catalogue of c o o l carbon s t a r s i n the Large M a g e l l a n i c Cloud has been presented. The ca t a l o g u e i s expected to be complete to an I magnitude of about 13.5, the approximate l i m i t i n g magnitude of the o b j e c t i v e prism survey from which the- s t a r s were i d e n t i f i e d . The s t a r s were k i n d l y i d e n t i f i e d by Dr. B.E. a e s t e r l u n d from p l a t e s he o b t a i n e d a t the Uppsala Southern S t a t i o n on Mount Stromlo. F i n d i n g c h a r t s and e q u a t o r i a l c o o r d i n a t e s f o r the 309 s t a r s which comprise the catalogue have been g i v e n . Such a catalogue should prove to be u s e f u l now that s e v e r a l l a r g e t e l e s c o p e s are o p e r a t i o a l i n the southern hemisphere. • The f a c t t h a t the d i s t a n c e to the Large M a g e l l a n i c Cloud i s well known allows many o b s e r v a t i o n s t o be made which otherwise would not be p o s s i b l e . I t i s important to o b t a i n as many a c c u r a t e absolute magnitudes as p o s s i b l e f o r carbon s t a r s as the data a v a i l a b l e now i s q u i t e sparse. Photometric o b s e r v a t i o n s on the VRI system of f o r t y carbon s t a r s , s e l e c t e d frcm the - c a t a l o g u e , were made i n order to i n v e s t i g a t e the photometric p r o p e r t i e s of carbon s t a r s with known absolute magnitudes. C o r r e l a t i o n s between a b s o l u t e v i s u a l magnitude and v a r i o u s photometric c o l o u r s have been searched f o r but no s i g n i f i c a n t r e s u l t s were found. The bulk of the s t a r s i n v e s t i g a t e d ' seem t o form an e m p i r i c a l b r i g h t g i a n t branch on the Mbol - V-R diagram. However t h i s c o u l d be a s e l e c t i o n e f f e c t as the photometric o b s e r v a t i o n s were r e s t r i c t e d to a b r i g h t e r than average qroup. Two m i l d l y p e c u l i a r s t a r s were 99 found in th i s sample of stars. These sere stars 1-12 and 6-6 i n the catalogue. They are warm luminous stars which exhibit substantial amounts of 1 3 C in their atmospheres. They also appear to l i e on the Ib supergiant branch in the Mbol vs (V-R) diagram. • :'•• • Spectra of seven members of the catalogue have also been obtained at a dispersion of 117i/mm. The spectra were obtained mainly to confirm that the stars were indeed carbon stars and to also note some of-the grosser features in the spectrum. It was found that- three of the seven stars exhibit J star c h a r a c t e r i s t i c s : " a higher than normal abundance of 1 3 C , as defined by Bouigue (1954) and Gordon (1967). This was unexpected as t h i s i s proportionally a much larger number of stars than for carbon stars i n our Galaxy. One star, 4-9, showed extreme J star c h a r a c t e r i s t i c s . The most outstanding feature i n the spectrum of 4-9 i s the 1 3C a*N band at ^6260. In many cases the- bands involving 1 3 C are stronger than the corresponding iZC ones. The evolutionary status of carbon stars i s not presently well understood.- It i s useful to place the stars i n a theo r e t i c a l Hertzsprung-Russell diagram to aid i n explaining t h e i r evolutionary development. Using the best avai l a b l e data for bolometric -corrections and using blackbody temperatures as e f f e c t i v e temperatures as argued for by Scalo(1976) the stars were placed i n a the o r e t i c a l H-R diagram. Although the positions of the stars are a b i t uncertain due to the e f f e c t s of 100 composition changes and u n c e r t a i n t i e s i n the d e r i v e d temperatures, the c o o l carbon s t a r s are almost c e r t a i n l y i n the double s h e l l source phase of e v o l u t i o n . In t h i s phase the s t a r s have two a c t i v e burning s h e l l s , one of helium and one of hydrogen. I t also.appears as though they are undergoing thermal pulses i n the helium burning s h e l l as d e s c r i b e d by Sh w a r z s c h i l d and Harm (1965).' In f a c t the s t a r s l e s s massive tuan seven s o l a r masses seem to be bounded below by the onset of these helium s h e l l f l a s h e s . I t i s g u i t e p o s s i b l e t h a t the helium s h e l l f l a s h e s are the mechanism by which i n t e r m e r i a t e mass s t a r s become carbon s t a r s ( I b e n 1975). The two m i l d l y p e c u l i a r s t a r s , 1-12 and 6-6, appear to be s l i g h t l y more massive than seven s o l a r masses. These s t a r s may ba pre-helium s h e l l f l a s h o b j e c t s although t h i s p o i n t i s u n c e r t a i n as models have not yet been c o n s t r u c t e d which are d e t a i l e d enough at t h i s p o i n t i n the s t a r ' s e v o l u t i o n . Now t h a t s e v e r a l l a r g e t e l e s c o p e s e x i s t i n the southern hemisphere a program of o b t a i n i n g medium d i s p e r s i o n s p e c t r a of as many of these s t a r s as p o s s i b l e should be s t a r t e d . Then i t may be p o s s i b l e t o de v i s e a c l a s s i f i c a t i o n system i n which the temperature,luminosity and abundance e f f e c t s can be s o r t e d out. Higher d i s p e r s i o n s p e c t r a should be obtained of some of the b r i g h t e r o b j e c t s t o a i d i n unerstanding the e v o l u t i o n a r y s t a t u s of the c o o l carbon s t a r s . 101 Bibliography, Bahng, L. 1966, i n Colloquium on Late-Type S t a r s , ed. M. Hack ( T r i e s t e : O b s e r v a t o r i o d i T r i e s t e ) , p. 255. Barnes, T.G. 1973, Ap. J . Suppl. Ser. No. 221, 25 , 369. B a r t h o l d i , P., Evans, D.S., M i t c h e l l , H.I., S i l v e r b e r g , E.C., S e l l s , D.C., and Hiant, J.R. 1972 A.J., 77 , 756. B e s s e l l , M.S., and Youngbom, L. 1972, Proc. A s t r . Soc. A u s t r a l i a , 2 , 1 5 4 . Bok, B.J., and Bok, P.F. 1962, M.N.R.A.S., J.24 , 435. Bouigue, R. 1954, Ann. d * Ap., JP7 , 104. Gatchpole, R.M. 1975, Pub. A.S.P., 87 , 397. De Vaucouleurs, G. 1955, A.J., 60 , 4 0 . De Vegt, C. 1974, A s t r . and Ap., 34 , 457. Dickens, R.J. 1972, M.N.R.A.S., .159 , 7.P. Eggen, O.J. 1972a, Ap. J . , V74 , 45. Eggen, 0.J. 1972b, M.N.R.A.S., J59 ,403. Gordon, P.C. 1967, d i s s e r t a t i o n , U n i v e r s i t y of Michigan. Gordon, P.C. 1968, Pub. A.S.P., 80 , 597. Iben, I. 1972, Ap. J . , 128 , 433. Iben, I . 1975, Ap. J . , J96 , 525. " Iben, I. 1976, Ap. J . , to be pu b l i s h e d . Johnson, H.L. 1966, Ann. - Rev. A s t r . and Ap., 4 , 193. Keenan, P.C, and Morgan, H.W. 1941, Ap. J . , 94 , 501 . Lasker, B.M., Bracker, S.B., and Kunkel, W.E. 1973, Pub. A.5.P., 85 , 109. • Lee, T.A. 1970, Ap. J . , J62 ,217. M a v r i d i s , L.N. 1967, i n Colloguium on Late-Type S t a r s , ed. M. Hack ( T r i e s t e : O b s e r v a t o r i o d i T r i e s t e ) , p. 420. Mendoza, E.E. 1967, B u l l . T o n a n t z i n t l a y Tacubaya Obs., 3 , 305. Mendoza, E.E., and Johnson, H.L. 1965, Ap. J . , 141 , 161. 102 Olsen, B.I., ana R i c h e r , H.B. 1975, Ap. J . , 200 , 88. Pa c z y n s k i , B. 1970, Acta A s t r . , 20 , 47. R i c h e r , H.B. 1971, Ap. J . , J.67 , 521. R i c h e r , H.B. 1972, Ap. J . (Letters) , 172 , L63. i R i c h e r , H.B. 1975, Ap. J . , 197 , 611. Sackmann, I . J . , Smith, R.L., and Despain, K.H. 1974, Ap. J . , 187 , 555. Sc a l o , J.M. 1973, Ap. J . , J 8 6 , 967. S c a l o , J.M. 1976, Ap. J. 1, 206 , 474. Scalo, J.M., Despain, K.H., and U l r i c h , R.K. 1975, Ap. J . , 196 , 805. > Scalc,J.M., and U l r i c h , R.K. 1975, Ap. J . , 200 , 682. Schw a r z s c h i l d , M. , and Harm, R. 1965, Ap. J . , 145 ,496. Shane, C D . 1928, L i c k Obs. B u l l . , "1.3 , 123. Smart, W.M. 1971, Textbook on S p h e r i c a l Astronomy(5th ed.; Cambridge:Cambridge :University Press),p. 278. Smith, R.L. Sackmann, I . J . , and Despain, K. H. , 1973, i n E x p l o s i v e N u c l e o s y n t h e s i s , ed. D.N. Schramm and W.D. Arn e t t ( A u s t i n : U n i v e r s i t y of Texas P r e s s ) , p. 168. U l r i c h , R.K. 1973, i n E x p l o s i v e Nuleosynthesis, ed. D.N. Schramm and M.D. A r n e t t ( A u s t i n : U n i v e r s i t y of Texas Press) , p. 139. U l r i c h , R.K., and S c a l o , J.M. 1972, Ap. J . ( L e t t e r s ) , 176 , L37. U l r i c h , R.K., and S c a l o , J.M. 1976, i n p r e p a r a t i o n . H a l l e r s t e i n , G. 1973, Ann. Rev. A s t r . and Ap., H , 115. westerlund, B.E. 1964, i n 1AU Symposium 20, The Galaxy and the Mag e l l a n i c Clouds, ed. F.J. Kerr and A.8. Rodgers(Canberra: A u s t r a l i a n Academy of S c i e n c e ) , p. 239. Westerlund, B.E. 1972, Proc. 1st European A s t r o n o m i c a l Meeting, ed. L.N. M a v r i d i s . Wing, R.F. 1967, Ph.D. D i s s e r t a t i o n , U n i v e r s i t y of C a l i f o r n i a , B e r k e l y . 103 Yamashita, Y. 1972, Ann. Tokyo A s t r . Obs., 2d Ser., V o l . 13 , No. 3.

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