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Carbon stars in the large magellanic cloud Crabtree, Dennis Richard 1976-02-08

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CARBON STARS IN THE LARGE MAGELLANIC CLJUD by Dennis Richard Crabtree B.Sc. University of British 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 this thesis as conforming to the required standard. The University of British Columbia August, 1976 © Dennis Richard Crabtree 1976 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. Depa rtment The University of British Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1WS ii Abstract A catalogue of cool carbon stars in the Large Magellanic Cloud is 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 in 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 l3C isotope. Using the photometric observations to place the stars in a theoretical Hertzsprung-Hussell diagram, it is concluded that (1) all forty stars are in the double-shell sourca phase of evolution and, (2) the helium shell flashes are responsible for the formation of the majority of cool N-type carbon stars. v iii Table of Contents page I Introduction 1 II Catalogue of Carbon Stars 5 III Photometric Observations 66 IV Spectroscopic Observations 7V Carbon Stars in the H-B Diagram 87 VI Summary 98 Bibliography 101 iv List of Tables page I. Plate Centres 8 II. Carbon Star Coordinates 9 III. Carbon Star Photometry 67 IV. Spectroscopic Observations 79 V. Properties of the Seven Carbon Stars 81 VI. Classification of Carbon Stars 82 List of Figures page 1. Finding Charts 27 2. V versus R-I 70 3. V versus V-I 1 4. V versus V-E 2 5. Mbol versus V-R 74 6a. Carbon Star Spectra, region 1 77 6b. Carbon Star Spectra, region 2 8 7. Bolometric Corrections 88. Colour Temperature versus R-I 92 9. Theoretical Hertzsprung-Russell Diagram 93 vi Acknowledgements I would like to thank my supervisor Harvey fixcher for his patience and enthusiastic support during the course of this work. I thank B.I. Olson for supplying many of the computer programs used in this study. I also thank B.E. Westerlund for kindly supplying the original charts on which he had marked the suspected program stars. I thank the University of British Columbia for support from a postgraduate fellowship. Finally I would like to thank the graduate students of the department for making the department such an enjoyable place to work. 1 I Introduction Among the stars classified as red giants there are many groups which show anomalous abundances of certain elements. One of these groups is the carbon stars. These stars show an enhancement of absorption bands of CH,CN, and including, in some cases, bands of molecules involving the 13C isotope. In the Henry Draper Catalogue these stars were originally classified as type R or N; N being reserved for the redder members. Shane (1928) reclassified these into subdivsions but it was discovered later that this system was not a true temperature sequence as was the rest of the Henry Draper system. Subsequently Keenan and Morgan (1941)• proposed the C-classification for carbon stars based on temperature and carbon abundance. However this system of classification has by no means solved the classification problem. Any classification system that is to be successful must be able to sort out the many differing abundances as well as the temperature sequence in these stars. Xamashita(1967) has devised a system in which he estimates the intensities of eleven spectral features as well as classifying each star cn the C classification system. One deficiency of the C system is that the sequence from C5-C9 probably does not represent a true temperature sequence ( Richer 1971 ;Scalo 1973) . Much of the theoretical work on carbon stars has been hampered by the lack of good absolute visual magnitudes for 2 individual objects. Seme results do exist( Gordon 1968;Eicher 1972,1975;Olson and Richer 1975) but the number of stars involved is not large enough to cover all the spectral subtypes and peculiarities observed in these objects. Tins follows from the fact that these objects are relatively rare in our Galaxy, attempts to measure the absolute magnitudes of individual objects run into the usual sort of problems encountered in this endeavor; no object is close enough to have a reliable trigonometric parallax, carbon stars are rarely members of clusters, few are members of binary systens, the iilson-Bappu effect is difficult to use for the R stars and impossible to use for the N stars,etc. The absolute magnitude problem is closely related to the problems of the effective temperature and radii or carbon stars. Only two carbon stars have had their angular diameters measured by the method of lunar occultation, 19 Psc and X Cue. A direct measurement of the radius is difficult since no carbon star is a member of an eclipsing binary nor has a measurable parallax. The temperature classes of the later stars in the C classification 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 like black-bodies than do M giants {Bahng 1966;Scalo 1973). Therefore any attempt to use a calibration between colour and effective temperature that is 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 exhibiting the products of nucleosynthesis in their outer atmosphere. The first part of this thesis contains a calalogue of carbon stars in the Large Magellanic Cloud. A catalogue of these stars should be a very useful ' document now that several large telescopes- are becoming operational in the southern hemisphere. If one obtains accurate absolute magnitudes and good medium dispersion spectra of carbon stars in the Large Magellanic Cloud it should be possible to better locate these stars in 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 relation between photometric colour and effective temperature, these stars are placed in a theoretical Hertzsprung-Russell diagram. The results 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 l3C isotope. A detailed discussion of the spectra is presented in section IV of this thesis. The catalogue itself is presented in section II while the 4 photometric observations are discussed in section III. Section V contains a discussion of the Hertzsprung-Russell diagram with respect to the carbon stars while section VI contains a summary of the results. 5 II Catalogue of Carbon Stars The most efficient way to discover and classify a large number of objects is to use an objective prism survey. This method is particularly useful in the search for objects whose spectra are easily separable from most other astronomical spectra. Such objects include emission line stars, planetary nebulae and carbon stars. The stars discussed below were identified by Dr. B.E. Hesterlund who has kindly supplied charts oi the Large Magellanic Cloud marking suspected carbon stars on them. Dr. westerlund identified 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 in the I band than either the B or V bands, thus the reason for using1I-N plates. This also reduces the overlap of"spectra on the plate since most other stars are much fainter (absolutely) in this region of the spectrum. The plates obtained reached to about 1=14 magnitude and the carbon stars were identified using the criteria established by .Nassau (cf. Mavridis 1967). The main indicators used to identify 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 is heavily overexposed. Hesterlund(1964) has given a preliminary discussion of this plate material emphasizing the distribution 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 rich in nebulosity and in blue stars. He also noted that they appear tc form clusterings, possibly in the shape of arms , and that the position of these clusterings agreed well with the structural 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 first section was at a scale of about 11.8" arc/mm while the second section, which also included all the first section, was at a scale of 27" arc/mm. The first set was measured in May 1974 while the second set was measured in August 1975. The method used to get frcm the X,Y position to right ascension and declination on the sky is that described by Smart (1971). Briefly, it consists of considering the tangent plane and a star's projected position on this plane if the telescope is not pointed directly at this star (as in a photograph). The point at which the tangent^plane contacts the celestial sphere(the point at which the telescope is aimed) is taken to be the origin. If ue take the meridian of this point, it projects into a straight line on the tangent plane. This line forms one axis for an orthogonal coordinate system on the sky. The other axis is taken to be a line drawn perpendicular to the first axis. 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 parallel to the 7 orthogonal axes on the sky. By using three standard reference stars, the plate constants relating the measured X-Y positions to the standard coordinate system can be calculated. Once the plate constants have been evaluated it is an easy matter to go from X-Y values to standard coordinates co eguatorial coordinates. The first 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 digitizer 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 all the stars were found quite easily at the telescope. Table I contains the approximate plate centres of each of the fields as well as the number of stars measured and the number of stars for which photometry was obtained. Table II contains a list of the coordinates for the epoch 1975.0 of all the suspected carbon stars. Finding charts for Table I Plate Centres r~?ield R. A. I I Dec. 1 1. I * 50 I -60O I ! 2. I *» 45 i I -69° 1 1 3. J 4 40 I I -720 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 -720 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 -720 i I 20. i 6 05 1 1 -750 1 1 23. I 6 30 1 i -690 1 i 24. ! 6 40 i 1 -720 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 in Fig. 1. The field of these finding charts is approximately 11 * arc by 16» arc with north to the top and east to the left. Table II Carbon star coordinates 9 L.M.C. Field #1 Star Right Ascension (1975) Declination (1975) 1 4h 52™ 28S -66°28!o 2 4h 53™ 2s -66°27 ! 0 3 4h 58m 36s -66°52!4 4 5h 0m 12s -66°28l2 5 5h lm 19S -66°52!9 6 5h 2m 9S • -67°18!l 7 5h 2m 17s -66°57!o 8 5 2 28 -67°12l5 9 4h 5 9™ 00S -65°57!7 10 5h lm 41S -65°5l!9 11 5h 2m 53S -65°58!9 12- 5h 3m 11S -66°2!9 13 5h 2m 47S -66°26!5 h m s , 14 5 3 25 -66°55.9 15 5h 4m 50S ' -67°13!l 16 £h 5m 50S -66°15'.3 17 4h 58m 43S -65°26l6 18 4h 58m 32S -65°22l2 . h m s ' 19 4 59 13 -64°59.0 20 5h 0m 26S -65° 2.'5 21 5h 2m 22S -65° 9^ 22 5h 2m 43S -65°ll!l 23 4h 53m 23S -64°37!9 24 h 50m 32s -67° o!7 Table II cont'd 10 L.M.C. Field //1 Star Right Ascension (1975) Declination (1975) 25 4h 49m 28s -67°16!3 26 4h 50m 34s -67o10.'6 27 4h 52m 30s -67°11 ! 1 .28 4h 57m 56s -67°19!4 29 5*1 0m 3s -67°14.'5 11 Table II cont'd L.M.C. Field #2 Star 1 Right Ascension (1975) Declination (1975) 4h 33m 51S -70°15!6 2 4h 39m 5S -7o°io!o 3 4h 40m 12S -7 0°13! 1 4 4h 49m 48s -69°58l8 5 4h 52m 54s -69°57 !4 6 4h 53m 44s -67°4l!4 7 4h 55m 25S -68°54!2 8 4h 54m 39S -7 0° 2'.3 9 4h 55m 11S -7 0° 2!8 10 4h 55m 43s -7 0° l'.9 11 4h 55m 35S -70° 9l7 12 4h 58m 39S -70°ll!3 13 4h 59* 19S -70°lo!3 14 5h 0m 23S -7 0°15!7 Table II cont'd L.M.C. Field //3 Star Right Ascension (1975) Declination (1975) 1 4h 41m 46S -70°52!5 2 4h 42m 34S -70°39'4 3 4h 4 4* 56s -70°31!3 4 . 4h 4 8m 43s -72°28.'o 5 4h 5lm 9S -72°45.'l 6 4h 53m 0s -73°18l5 7 4h m 50 15s -71° 3!o 8 4h 5 0m 35s -70°25!6 9 4h 53m 24s -70°38l3 10 4h 5 3m Is -71°15!2 11 4h 57m 2s -73°14\5 12 4h 55m 28s -70°21 '.9 13 4h 5 6m 14S -70°2o!o 14 4h m 58 3S -70D5o!4 15 4h 57m 50S -71°21 !8 16 4h 5 8m 41S -71°58!5 17 " 5h Im s 52 -7 2° 56'.6 18 5h om 36S -71° 14*. 5 Table II cont'd L.M.C. Field if h Star Right Ascension (1975) Declination 1 5h 7m . 8S -64°27!.2 2 5h 8m . 44s -64°42.3 3 5h llm 31S -64 011.'9 4 5h 12m 31s -64°14!l 5 5h llm 50s -65° 9!8 6 5h llm 42s -65°16!1 7 5h 15m 17s -65° 9.6 8 5h 16m 9S -64°52!l 9 5h 17m 10s -64°48!5 10 5h 19m 45S -65° 4.'2 11 5h 2 3m 2S -64°54.7 12 5h 4m 55S -64°30'.7 13 5h 9m 21s -64°28:2 14 5h 16m 34S -64°2l!l 15 5h 8m 54S -65°43.!7 16 . 5h iom 44S -65°42'. 1 17 5h 12m 6S -65°47'.6 18 5h 12m 55S -65°43l3 19 5h 15m 33S o ' -65 47.5 20 5h 5m 59S -65°58.8 21 5h 7m 46S -66° 5.5 2 2 5h 3m 32S -66°23l2 23 5h 6m 13S -66°26!4 24 ' 5h 8m 24S -66°26!8 Table II cont'd L.M.C. Field #4 Star Right Ascension (1975) Declination (1975) 25 5h llm 44s -66°52l7 26 5h 6m 44s -67° 4*.9 27 5h 10m 50S -67°27 '.2 28 5h 15m 19s -67°15:9 29 5" 16m 28 30 h 19m 39s -67036!6 31 5h 20m 44s -67037!4 32 5h 15m 4s -64°48!4 33 5h 14m 15s -65° 3^ Table II cont'd L.M.C. Field #5 Star Right Ascension (1975) Declination (1975) 1 4h 59m 57S -67°l4!l 2 5h om 47S -69° 9*0 3 5h 2m 10s -68°55!6 4 5h 2m 7S -68°46!l 5 5h 3m 38s -68°35!5 6 5h 3m 35S -68°19l7 7 5h 3m 43s -67°39\l 8 5h 8m 54s -67°26!2 9 5h 4m 18s -69°15!6 10 5h 7m 5S -69°58!2 11 5h 9m 11s -69°28!4 12 5h 9m 24s -69°13!2 13 5h iom 25S -70°24l2 14 5h 16m 14S -69°57!1 15 5h 18m 49S -70° l!9 16 5h 2im 59S -69°56l6 17 * 5h 24m 43S -69°21\l 18 5h 2 8m s 20 -70°2l!6 19 5h 27m 40S -69° 6!8 20 5h 27m 20S -67°23!6 21 5h 2 9m 46S -68° 4l6 22 5h 3 0m 28s -68°57\l 23 5h 3 2m 57S -70°12!8 24 5h 33m 34S -68°51!4 Table II cont'd L.M.C. Field #6 Star Right Ascension (1975) Declination (1975) 1 5h 0m 24S -70°15!8 2 5h 0m 46S -70°39l4 3 5h Im 28S -70°38.'2 4 . 5h 2m 4S -70°53!3 5 5h 5m 4S -70°3o!9 6 5h 5m 6S -70°27!6 7 5h 6m 14s -70°19:4 8 5h 8m 16s -71° 7.*8 9 5h 13m 10s -71° K6 10 5 11 27s -70°46!l 11 5h 15m 8S -73°17l8 . 12 5h 16m 8S -73° 18.'2 13 5h 26m 4s -73°19.'8 14 5h 26m 41S -73° 2!8 15 . 5h 28m 45S -73° ^\(> 16 5h 24m 44S -72° 9l7 17 5h 27m 20S " -72° 12.'7 18 5 32 40 -70 53.1 19 5h 33m 54s -70o53!4 20 5h 35m 10S -71° llA 21 5h 37m 12s -70° 58!6 22 5h 38m 0S -70° 49!l 23 5h 38 14 -72° 9.3 24 5h 3 8m 58S -7 2° 2*. 4 25 5h 39m 19S -72°10!4 26 5h 3 9m 16s -7 2° 5.'o Table II cont'd L.M.C. Field #6 • Star Right Ascension (1975) Declination (1975) 27 5h 41m US -72°30.7 28 5h 38m 35S -71°36.0 29 4h 59m 57s -71° 1! 6 .30 5h 2m 29S -71° 3!9 h 9 <? 1 31 5 4* 9 -72b19.4 32 5h 7m 11s -73° 9.4 33 5h 8m 6s -72°49.'2 34 5h 8m 52S -72°47l3 h m o ' ' . 35 5 10 7 -72°17.8 -36 5h 10m 32S -71°47 \$ 37 5h 13m 36S -70°52.'5 ,37a 5h 12m 29S -70o50!3 38 5h 12m 49S -71°47 !7 39 5h 13m 50S -72°55!l 40 5h 15m 55S -72°33!2 41 5h 14™ 44s -71°44.7 42 5h 16™ 15S -71°52.'4 43 5h 16m 35S -72°14l2 44 5h 18m 32s -71°53!4 45 5h 17m 38s -71° 4U 46 5h 18m 33S -70°57l7 47 5h 20m 21s -72°43l3 48 5h 22° 20S -72°30.'5 49 5h 22m 13S -72° 5.'3 50 5h 23m 26S • -71°59l0 Table II cont'd L.M.C. Field #6 Star Right Ascension (1975) Declination (1975) 51 5h 23m 11s -71°44!5 52 5h 24m 4S -71°47!2 53 5h 21m 34S -71°29.*8 .54 5h 23m 5S -7 10 25 .'6 . 55 5h 23m 44s -71°34:3 56 5K 23m 59S -71°27.'9 57 5h 24m 50S -71°26!o 58 5h 23m 44s -70°45h 59 5h 24m 56s -71° 5!4 60 5h 24™ 53S -70°59!8 61 5h 27m 34S -7'p058 !3 ... 62. 5h 28m 8S -70°55!4 h in s o ' 63 5 26 56 -70 40.3 5h 27" 33S -70O40!5 65 5h 26m 26S -72°13.'5 66 5h 30m 47S -72° 4!9 67 5h 3im 58S -71°44!5 68 5h 32m 16S -710ll!9 69 5h 33™ 2s -71°32!7 70 5h 33m 28S -71°34!.9 71 5h 33m 6S -71°27 !8 72 5h 34m 6S -71°23!o 73 5h 33™ 53S -72° 4 ! 9 74 5h 34m 37S -71°59 ! 1 75 5h 35m 27S -72° s!'7 76 5h 38m 4S -70°55!9 Table II cont'd L.M.C. Field #7 Star Right Ascension (1975) 1 5h 31m 11S 2 5h 3Am 24S 3 ' 5h 35m 41s Declination (1975) -65°33!2 -67°29.5 -66°21.8 Table II cont'd L.M.C. Field #8 Star Right Ascension (1975) Declination (1975) 1 5h 44m 33s -69° 8!6 2 5h 48m 21s -67°14.5 3 5h 4 8m 3s -69°22!1 .4 5h 5 2m 42s -67°54.5 5 5h m 53 25S -68°46!1 6 6h 5m 56S -69°27!2 7 6h 7m 41S o ' -70 31.0 8 6h 7m 33s -69°26.2 9 6h 8m 43s -69°58\h 10 6h 7m 23S -67°52l4 11 6h 7m 41s -67°52l0 12 6h 8m 47S -68°15'.9 13 6h 9m 10s -67°12l3 14 6h iom 50S -67°16!5 Table II cont'd L.M.C. Field #9 Star Right Ascension (1975) Declination (1975) 1 5h 45m 19S -71°35.2 2 5h 45m 24s -70°38.2 3 .... 5* 47m 23s -70°33!5 4 5h 4 6m 49s -71°13l8 5 5h 4 8m 12s -71°13 ! 0 6 5h 48m 6s -70°58l4 7 5h 48* 54s -71°42.'8 8 5h 4 9m 37s -71°39l2 9 5h 4 9* Is -70°46!o 10 5h 49™ 13s -7 0° 44 .'8 11 5h 4 9* 55S ' -7 0°52.'6 12 5h 50m 7S -70°59l5 13 5h 5 0m 31S -7 0°45l2 14 5h 5lm 45S -72°30!7 15 5h 5 2m 25S -72°2l!3 16 5h 5 2* 30S -7 0° 36 .'5 17 5h 5 2* 41s -71° 26.'5 18 5h 53* 4s -71°35!l 19 5h 53* 22S -71°37 ! 1 20 5h 54m 4S -70°25l5 21 5h 54m 23S -70°33 ! 3 22 5h 54m 18S -71° 0.*5 23 5h 5 6m 21S -70°48!o 24 6h om 18S -71°11 \l 25 6h . 7* 9S Table II cont'd L.M.C. Field #9 Star Right Ascension (1975) 26 6h 5m 40S 27 6h 6m 31S 28 6h llm IIs 29 6h 12m 48S 30 6h 13m ios 31 6h 16m 9S 3 2 6h 17m 50S 33 6h 2 0m 2S 34 6h 19m 19S 35 6h 19m 46S 36 6h 2 2m 43s Declination (1975) -71°21!9 -7 0°44*9 -71°lo!9 -72° 3^ -72°lo!4 -71°44!2 -71°36!l -72°28 ! 6 -71°16l8 -71° 9l6 -72°37 !o Table II cont'd L.M.C. Field #20 h m , , s 23 Star Right Ascension (1975) Declination (1975) 1 5h 57™ 24s -73°52!4 2 6 9 14 -73°50.1 3 . 6h 14m 22S -73°53ll 4 6 18 0s -74° 1.3 Table II cont'd L.M.C. Field #23 Star Right Ascension (1975) 1 6h iom 27S 2 6h llm 38s 3 6h llm 56S 4 6h 12n 45S 5 6h 13m 8S 6 6h 13m 21S 7 6h 13m 44s 8 6h 15m 39S 9 6h m 16 18s 10 6h 16m 55s 11 6h 17m 38s 12 6h 16m 52s 13 6h 16m ios 14 6h 16m 31S 15 6h 16m 19S 16 6h 16* 3 5S 17 6h 17m 7S 18 6h 18m 14s 19 6h 19m 21s 20 6h 19m 26S 21 6h 19m 24S 22 6h 2 0m 15S 23 6h 2lm 20S 24 6h 22m os Declination (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. Field #23 Star Right Ascension (1975) Declination (1975) 25 6h 22m 10s -67 °59l4 26 6h 22m 2 6S o » -67 52.3 27 6h m 23 31s -68°35!9 28 6h 23m 48s -68°57!o 2 9 6h 25m 55S -68o10.'8 30 6h 26m 21S -68°46.'8 ) 31 6h 2 6m 42S -68°49.'2 32 6h 27m 16S -68 °52!0 33 h 6 28m 56S -68 °54!6 34 6h 3lm 21S o » -69 11.1 35 6h 14m 16S -68°48!8 36 6h llm 37S -68°52.'8 37 6h llm 57S -68 °58\l 38 6h 13m 55S -68 °58l7 39 6h ll" s 54 -69°15.'l 40 6h 13m 24S -69 °14 ! 4 41 " 6h 12m 21s -69 °44 ! 6 42 6h m 11 50S -7 0° 1.'3 43 6h 13m 46S -70 °13 ! 0 44 6h 15m 6s -70 ° 0 ! 2 45 6* 15m 15S -70 °29 !3 46 6h 24m 47S -70o13.'6 47 6h 24m 39S -69°53l2 48 6h 24m 40S -69°44!l 49 6h 25m 5S - 6 9 °4 4 ! 0 50 6h 2 9m 3S -70°20l4 51 6h 13m 38s -69°28 !3 Table II cont'd L.M.C. Field #24 Star Right Ascension (1975) Declination (1975) 1 6h 26m 47S -71°41.8 h n. s 2 6" 29 34° -70°55.5 3 6h 30m 42s -71° 0.6 .... ». . •„<"-* />'<•*•* ~ Fig. 1 Finding Charts LMC Field #1 \ . * . " * * / . 0 I • . • T 7 •I .. .... Y.^:r.'- .•.-» IS*. • • • v rig-"* •*•«-• Fig. 1 cont. LMC Field #1 N3 00 29 .... • ... * • r * it*-" *v% -r.-,* • ~ v"' •'" •••'4 y.yr^i.VVJ-'mrv, matt .v* f * sis y> * - - "v"*? V • • • •• ••• *v '•••• 5 , . ' • • sr..'- • . ! . • ' ' V. Si, %-»W4 / . . • • • * 4 •'•*••»• .v ' - ' * • • . .. . • - • %*.mz ". - -'it ' >••>:" •' »• , ;•• r.- < »t • • • j • , \*sj"'**»••'. •••• 'V.5i ?» o 7*J?* - • • • * •'- »*:•> rH OJ •H U a 4J C o o •H Fig. 1 cont. LMC Field //l co o V Fig. 1 cont. LMC Field #2 H .v Fig. 1 cont. LMC Field #2 S3 !.\'-;- :> vti V •••• V ' - A .. .•'«."•"" '.''..•>-#,v^'-••" v '.' ..•*•...•• '•*.•* vi • • * i : J • * • v • v. • • *< i • •. . - . . • • ... Fig0 1 cont. LMC Field #3 • - ft'. u> Fig. 1 cont. LMC Field //4 01 •j "~~ -*. . * • t • .* • . • • - . . • y '3 • 1 • • • f. , • •* • i '' • • ' V • '"^ B» • SI * ' * ! < . i • ... * • « • 1 Ms*. r 1 I I 16*. • © • k-I,. 1 • / Fig. 1 cont. LMC Field #4 U) ON Fig. 1 cont. LMC Field #4 l»- Sr * • « - * • I ' r**» ••">•» 39 $4* fe . • . » • i -V'] •Bill rlJMiiTT Tin'ii_mjj 5kV*; . •'•>! iff"*1, >•< tk: ... . " •••• • ' • • • . * * * '• • * -7 =& H •H a o o to « • " • • a ' «.»,"» .A* : ' t -4 • • ., : • 't. i *-».... 1 r • • • .. ^ • • • • . v • • % •. ***•. • •••• «i • ,: • • • / • >, " hO''" - • • '••••'•3 •>. •» v- *; -•••V-• * '--ii •••• K ; if:. trim . • V 4*.-.' . i.v. 1 • • . . t * * *• •.. . I N. pre • ' • • • k -*. Ax \ » «• ta ^ ft ksi * » 3».' •••• r.*^>^-:;i:;<? Be' •••••• • « *>r - J"- . • * V «,*t. * vasrWi?*J k*.*H>. iA.* . v *, . .f , JVC* •/<•• ^ * -»t--Fig. 1 cont. LMC Field #6 r.j>t. 0 * IL" • 7, • * . • <.,v-.... *4 *. o»» •».•* a) •rl a 4-> c o o to Fig. 1 cont. LMC Field #6 i '•* » f -'V-.. '*.-•••• • t m - yryv<w»'ai —, ^ » 1- T>1 • *. 1 • • •••• * • • • , iff Jf . e * ** * " ..• ° » » a . 7 * '•. ' .• • \v ..... •• • ' *.i • .. •; . •' ' •• • , •-. :': • . - »*i  ; • ."6. .' . •V. .«v • Fig. 1 cont. LMC Field #6 : y I • • J //v .1 47 ir. • : • .• #<:\ '•*.•: »/•'•'"> ' .* v " v' Li » ? ' \>"J* .» . * ' % • • . • ; ' • L •*- f • . ' • • ' ' t-.* * • : :*f u- •: . y - ... : . \ -r- .-••»•*, c. - * * ••*...•• . » •. >v:, «... • .'*v.. •• * * «, 1 »• * V' • •A W.1 • ... •' .»>.. . ".• •H fe CJ 2 i-l 4J o a 6.0 •H PH ;..v:.--.....".v..^ .v i •••'••Lr'.*'Tv .• •.. « • > • *• .. • • ' :-ml * WD .<"••>:••v•:v>1 . - *.^**YYY Y '^Y Y / * Y •V*" , M ' • . ». . . •Y ,S7Y' 4 v A. •Y.^>* 'i, -T-:; > ;>•:• ,v%V*<i •» ,c.«8 . Y • • q '. Y .-V V\ V- .Y.'-' V Y. v...f VV".V^: »A.- Y-' :i.Y#Y-:j Y.:-v\-r-:-YY *• ^ •4 tSUkj. i.4liJ<! <Y;Y Fig. 1 cont. LMC Field #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 rv •;.••< a 9 ^h'iv^.<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 '*-•' « • " Fie. 1 cont. LMC Field #6 o i Fig. 1 cont. LMC Field #7 Fig. 1 cont. LMC Field #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. Fig. 1 cont. LMC Field #9 i Fig. 1 cont. LMC Field #23 64 • Y.-« •.•vi •• • • i E t * * f. - * • '• •: Y •.. • j ft-;*:,- -• v 1 ^"*'Y: •••'•;^Y^-T!\>.!^gwiw»^ I- • • t~K-:, w% i • ,* r ri fe'*- • •' *' M - * f l" • * *) p ' •"5* • Y . • Y •Y4 • ••Y fv; -Y | • .:* 1 • it * k " ' | • • • Witt* j ' • ' '' *". * J Vio. 1 rnnt. T.MH Field #24 S 66 Iii £]l££2J§££ic Observations The absolute magnitudes of carbon stars are very poorly known. No carbon star is near enough to have a reliable trigonometric parallax, carbon stars are rarely members of binary systems and they are seldom found in clusters. All the forementioned facts make it difficult to obtain absolute visual magnitudes - for these objects. However the Large Magellanic Cloud is near enough and its distance is well enough known so that the absolute magnitudes of carbon stars in the Large Magellanic Cloud can be accurately determined. To this end photoelectric measurements of forty of the stars in the catalogue have been obtained on the VRI system. The VRI photometry was obtained with the one metre telescope on Cerro Tolclo on the nights of Dec. 17-22 1974. Table III contains the photometric data for all the stars which were observed along with comments for some of the stars. For two of the stars only the R-I colour was obtained and for one other star only V and V-R was obtained. The stars for which spectra were taken will be discussed in Section IV. The photometry was calibrated on each night using an average of seven standard stars, and extinction coefficients were calculated for each night. The average extinction coefficients for the three nights were: KM=0.111, K (V-R) =0. 024, K (S-1) =0.088. These average extinction coefficients agree very well with those obtained in previous observing runs(Olson, private communication). The average rms deviation for the standard 67 Table III Carbon star 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 in 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 68 Table III 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 in 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 this' sample of forty carbon stars for which the absolute visual magnitude is known to a fair degree of accuracy, a relationship between absolute magnitude and various parameters can be investigated. However one must remember that we are working with a restricted sample of stars, in the sense that these forty stars are on the average brighter than the average carbon star in the Large Magellanic Cloud. This arises from the fact that only a one metre telescope was used to make the observations. This restricted the observations to the brighter members of the catalogue. The brightest carbon star observed in the visual region has an apparent visual magnitude of 13.87 while the faintest has a magnitude of 16.80. If one assumes a distance modulus to the Large Magellanic Cloud of 18.5 (westerlund 1972) the absolute visual magnitudes are -4.6 and -1.7 respectively. Fig. 2 is a plot of apparent visual magnitude versus the photometric colour, S-I. It can be seen that in general the fainter stars are also the redder stars, although the scatter around the mean line is guite large. One star, marked by the hourglass symbol seems to be discordant with the rest of the sample. It is possible that this star is 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 in (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 ^AA A A A z^A A A A A <!> A 0 D.B 1.0 1.2 1.4 R-I 71 CD 10 LO . Figure 3. V versus V-I A A A A rv LO . CO in —1 in in. LCI -a". ca rn 1 .B 2.25 A A A ,A 1 A A A A A A A AA & ^ 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 in our Galaxy. It is possible that they are high latitude CH-stars although the red spectra available do not allow a distinction to be made between late type carbon stars and CH-stars. In this case blue spectra would be needed to verify this possibility. 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 in Fig. 2. - In these latter two diagrams the relationship between magnitude and colour is not as tight as in the V versus (R-I) diagram* From these three diagrams it does not appear that any tight correlation can be found between visual magnitude and photometric colour index for the red and near infra-red colours. Figure 5 shows a plot of absolute bolometric magnitude versus (V-R) • for the carbon stars in this sample. The bolometric corrections used were those found by Olson and Richer (1975) in their investigation of the correlation between bolometric correction and photometric colour. The solid lines represent the mean location of the Ib supergiant branch and the class III giant branch. The carbon stars in this sample seem to form quite a definite branch between the Ib supergiants and the normal giants. However this appearance may be somewhat artificial as the sample of carbon stars is somewhat brighter well as enhancement Figures 3 75 than average, as least in the vi to say that the cool carbon st bright giants to ordinary gi magnitude. sible region. It would be safe ars seem to cover the range from ants in absolute bolometric 76 IV S£ectrosco£ic Observations Carbon stars'exhibit one of the most complex spectra of any astronomical object in the visible and near infrared regions. This spectral region contains a multitude of atomic lines as well as the absorption bands of such molecules as 12Ci*N,12Cl2C,*2CH and the other isotopes of these species. The complexity of their spectra has always hampered attempts to interpret their spectra in terms of temperature, luminosity and abundance effects. Any attempts to correlate luminosity and spectral features have been hindered by the lack of good absolute magnitudes for a sufficient number of carbon stars and because of differing abundances. There'are just not enough absolute magnitudes of sufficient accuracy known to determine the luminosity from the spectrum of any given carbon star. This of course assumes that it is possible to do this for carbon stars as it is for most other stars. Since the :carbon stars in the Large Magellanic Cloud are relatively faint a large telescope is needed to get good slit spectra of a "large sample of these stars to investigate luminosity effects. The main purpose of my spectroscopic investigation was to confirm that the objects were indeed carbon stars, by observing molecular i2c*2C bands, and to note some of the grosser features in the spectra. Slit 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 star spectra, region 1 Figure 6(b) Carbon star spectra, region 2 79 Tololo in 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 details of the observations are found in table IV. On such long exposures with an image tube the number of ion events becomes significant and hence the background fog level 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 02.9 | Dec. 14/74 J 91 min. 5 39 19 | -72 10.4 I Dec.14/74 | 85 11 5 00 26 1-65 02. 5 JDec.15/74 |118 »• 5 05 06 1-70 27.6 |Dec.15/74 J 92 " 5 38 00 1-70 49. 1 |Dec.16/74 i 123 » 5 17 10 |-64 48.5 | Dec. 16/74 |91 " 5 02 04 |-70 53. 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 in 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"°^ is typical of the carbon Long Period Variables. In general the only atomic lines seen were the D-lines and H°<. Tracings of the spectra over the wavelength interval 850-6950A are shown in Figure 6 (a) while Figure 6(b) shows the interval from ^5000 to ^5900. These tracings were produced by digitizing the spectra at 5/c intervals on the Joyce-loebl•Microdensitometer of the Geophysics and Astronomy Department at OBC. The resulting data was smoothed with a nine-point triangular filter to reduce the noise. For comparison, two Galactic carbon stars were also reduced in the same manner. The Large Magellanic' Cloud has a systematic velocity relative to the sun of about 250 kmsec-1. Almost all of this is due to solar motion. This enables one to ascertain whether a star is a probable member of the Cloud or not just by measuring the radial velocity of the star. Several spectra of Galactic carbon stars were obtained each night to serve as radial velocity standards and since the only atomic lines definitely present in the Large Magellanic Cloud stars were the D-lines of sodium, I had to rely on the position of the molecular band heads for radial velocity measurements. This procedure admittedly introduces more error into the velocity measurements but the result should still indicate whether or not the star is a • member of the Large Magellanic Cloud. The wavelengths of several band heads in the Galactic carbon stars were measured and :after correcting for the motion of the earth a set of standard wavelengths was produced. The positions of the 81 corresponding band heads in the Large Magellanxc Cloud carbon stars were'then measured relative to this set of standard wavelengths. The final radial velocity was found after correcting for the earth's motion in the direction of the Large Magellanic 'Cloud; The results are shown in Table V along with other pertinent quantities for the seven stars. Ihe number in parentheses is the probable error in the radial velocity. The average velocity of 245 kmsec-1 is in excellent agreement with the systematic velocity of the Large Magellanic Cloud found by Bok (1966). 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 13.87 |1.14 I2.00 1-4.61 -5. 7 | 6-6 | 346(66) J14.27 I 1.33 J2.32 j-4.21 -6. 0 I6-4 I 198 (50) |15.29 | 2. 07 |3. 29 1-3.2| -6. 6 16-22 | 189 (34) 115.39 | 2.06 J3.17 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) | 15.57 I 2. 12 I3.33 1-2.91 -6. 5 |4-9 j 253 (17) | 15.77 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 characteristics of the program stars quite well, paricularly Figure 6 (b). Prominent features are marked on the tracings. Night sky lines are indicated by n.s. while plate flaws are 82 marked by a dot. Table VI gives the C-classisication as defined by Yamashita(1972) for each star together with an intensity measure for each specific line or band on Yamashita's scale. These intensities were determined by comparing the Large Magellanic Cloud carbon stars with the Galactic ones. (D= Na D-lines; CA = i2CizC bands at XA5636,6T91; 13=i*Ci3C b^nd at X6168 and i3Ci4N band at )*6260; CN="Ci*N band at X5730 and ^6206; Li- LithiumI 6708 ; H«< — X6563) A discussion of the spectrum of each individual star follows. Table VI Classification 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 Li 0 0 0 0+ 0 0 0 0 0 e? 0 0 0 0 1-12 - This star was the bluest and brightest(in V) of any of the stars observed. It shows moderate J-star characteristics as defined by Bouigue(1954) and Gordon (1967) with the i3Ci*N (4,0) band at )\6260 83 slightly stronger than the corresponding 12Cl+N band at )i6206. The (0,0) band of i2C"C is of moderate strength but the (0,1) band is suprisingly weak. The (0,2) band of i2ci2C is barely visible while the (1,3) and (2,4) bands are present but weak. The Sodium D-lines are present with seme strength but Li \6708 and H<*> are definitely not present at the resolution used. 6-6 - This star was the next bluest one observed as well as being the second brightest visually. The (0,0) and (0,1) bands of 1ZC12C are moderately strong and are very well defined. The +2 sequence of 12C12C, (0,2) , (1,3) , and (2,4) ,is present but weak. The wavelengths of these features are ^6191, \ 6122,and ^6060 respectively. The *2c*3C band at X6168 is present with considerable strength as is the l3C1*N(4,0) band at ^6260, implying a relatively high abundance of *3C. Although the spectrum is somewhat weakly" exposed shortward of W 5000 A there is an indication that the Merrill-Sanford band(probably SiCjJ is present at^ 4977 . The sodium D-lines are quite strong but they are not resolved. There is no trace of either H or Li/\6708. 6-4 - In the spectrum of this star the IZQIZQ (0,1) and (0,0) bands are weak to moderate in strength while the 84 (1,3) and (2,4) band heads are much stronger. There is a weak trace of izc13C at ^6168 and the region from ^6260 to ^ 6285 seems to be depressed slightly implying a somewhat higher than normal abundance of l3C. The l2CJ*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 12C12C(0,0) and (0,1) bands are of moderate strength and are quite well defined in this star. The 12G14N 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 Li ^6708 line appears to be present with considerable strength along with the KI line at ^7699. There is 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 in 6-22 than in WZ Cas while the Na D-lines are weaker.'• The abundance of *3C in this star appears to be normal. 6-25 - The sodium D-lines are present but weaK. while most of the i2cl2C bands appear to be of moderate strength. 85 The abundance of 13C seems to be normal as the l2Ci3C band is present but very weak and the ^c14!) band at V)S6260 is not at all visible.. Neither Li ^6708 nor He* are present. 1-20 - All the 1ZC>2C bands in this star are very well developed. The +2 seguence is especially strong. The abundance of l3C appears to be normal as the i3c1*N band at ^6260 is not visible while ^6168, *zcl3C, is visible but weak. The sodium D-lines are of moderate strength and there is no trace of Li ^6 708 or JP< . 4-9 - This star shows an extremely high abundance of 13C as displayed by the strength of the i2C13C and l3Cl*M bands. The most outstanding feature in the entire spectrum of 4-9 is the(4,0) band of i3c1*N at X 6260. The1 corresponding I2QI4JJ at X 6206 is present but weak. The l2Cl2C band at ^5636 is very strong but the i2C12C band at X&191 is actually weaker than the corresponding i2c13C band at ^6168. There may be two i3cn3C bands present, the (1,3) band at "X6080 and the (0,2) band at)\6145. The Na D-lines are weak but this should ,be considered in light of the fact that the entire region frcm ^\5750 to ^6150 is depressed due to absorption from i2cl3G and i3cl3C as is the case for the more extreme Galactic J stars (Yamashita 1972). 86 It is also possible that this star shows a weak KI line at ^7699. All of the stars above display molecular bands of Cj,. It is perhaps significant that three of the seven show higher than normal abundances of •• 13G. This is proportionally more stars than for Galactic carbon stars. It is also suprising that none of the stars show definite H~- emission, which is characteristic of the Long Period Variables. It is possible that the two bluest carbon stars(1-12 and 6-6) are not members- of the Large Magellanic Cloud but are actually high latitude CH stars. 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 will assume that all seven are members of the Large Magellanic Cloud. 87 I Carbon Stars in the H-R Diagram The precise evolutionary phase (or phases) of caroon stars is not presently understood. They are believed to be highly evolved objects which are exhibiting the products of nucleosynthesis in their spectra. Besides determining their evolutionary status from data on masses, ages, spectra, and atmospheric abundances, one would like to know their position in 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 in the theoretical H-R diagram it is necessary to know the absolute bolometric magnitude as well as the effective temperature of the object. First I will 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 distribution over all frequencies to find the total energy emitted by the' object. However this can only be done for the brighter objects; Mendoza and Johnson (1965) have done this for a few dozen Galactic carbon stars, with photometric observations extending far out into the infrared where most of the carbon star's radiation is emitted. It is fortunate that their results show a good correlation between the calculated bolometric correction - and the (V-R) colour index for both R and N stars. Olson and Richer(1975) have investigated this correlation and find the relationship shown in Figure 7. There are two 88 Figure 7. Bolometric corrections • N - s t a r © R-slar •~5> ? y / / 0/ e / / o / © s V-R 2 89 different relations shown; one for the R stars and one for the S stars. Since the R stars are much fainter(absolutely) than the N stars it is expected that all the carbon stars observed in 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 slightly bluer in (V-B) than the bluest Galactic. N star- used in the calibration the bolometric correction was calculated by simply extending the linear portion of the calibration curve for N stars to find the correct value. It is expected that the bolometric corrections are good to about 0.3 magnitudes. I have neglected interstellar reddening in obtaining the absolute bolometric magnitude for these stars for two reasons. First, there is very little reddening in the direction of the Large Magellanic Cloud (Bok and Bok 1972). Second, any reddening which is present will tend to move the stars along the calibration curves rather than across them. This is because'the reddening will cause the star to appear fainter visually but it will also increase the bolometric correction, hence the two effects tend to cancel out. The problem of assigning effective temperatures to the cool carbon stars is not as easily resolved as the question of bolometric' corrections. First, there are only two N stars for which radii have been measured by the method of lunar occultation. Further, no N star is a known member of an eclipsing binary system so that the radius may not be determined by this method. It is not possible to use the calibration based on various photometric colours set up for M giants as the 90 sources of opacity are- quite different for the carbon and H giants. In fact the late type carbon stars radiate more nearly like 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 calibration. 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 typical total spread in derived blackbody temperature is only 50-200°K. The requirement that the blackbody temperatures be consistent is a necessary requirement for their use -as effective temperatures but it is not sufficient. Thus it-is 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 significantly different results. Bartholdi et al. (1972) have measured an occultation angular diameter for the N star, XCnc. Using Mendoza's(1967) relation between Te and-bolometric correction to eliminate the bolometric correction, they find a Te of about 2500°K. However, aendoza's (I-L)' temperatures are probably too small. If one uses the bolometric correction derived from the (V-R) colour index a Te of about 26400K is obtained for a fully darkened disk or 2810QK for a uniformly illuminated one. Various authors have measured 91 occultation diameters for 19 Psc(Lasker et ai 1973; De Vegt 1974) and analysed them for effective temperatures. Scalo(1976) adopts a temperature of 3050±2000K for 19 Psc and 27QO±100°K for X Cnc after considering all the derived values. Figure 8 shows a plot of colour temperature as a function of (R-I). The filled circles are the calibration of G and M giants by Johnson (1966) while the open circles are the calibration of M giants given by Lee (1970). The open squares are the calibration of & supergiants by Lee(1970) and the crosses represent the calibration of late type Miras by Mendoza(1967). The solid line represents the blackbody relation while the filled triangles are the approximate positions of the two carbon stars for which angular diameters have been measured. Note how the two carbon stars fall closer to the blackbody line than to the H giant calibration. Therefore it seems reasonable to use blackbody temperatures derived from the (R-I) colour index. In order to help understand the carbon star's place in stellar evolution it is convenient to place them in a theoretical H-R diagram. Figure 9 is such a diagram. The forty stars for which photometry has been obtained are plotted. The effective temperatures used were those derived from a blackbody curve fitted to the (R~I) colour while the bolometric correction used was that of Olson and Richer (1975) from (V-R) photometry The theoretical evolutionary tracks shown have been adopted from Scale (1976) and Scalo,Despain and Ulrich(1975) and references Figure 8. Colour temperature versus R-94 cited therein. All these models represent stars of disk composition, The thinner lines correspond to the first ascent of the giant branch to core helium burning, as well as double shell source models. The double shell source models are the ones lying to the right of the diagram. The thick line represents the locus of'points at which the first helium shell flash 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 this line have two active burning shells and are undergoing thermal pulses in the helium shell at fairly regular intervals. The broken line corresponds to the mean position of supergiants of luminosity class lab. The seven stars'from'Table V for which-spectra were obtained are identified 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. Ulrich and Scalo(1976) esitimate that the uncertainties in the temperatures of the double shell source tracks due to possible errors in convection theory and in the atmospheric opacities is- no more than ±2000R. Scalo(1976) estimates that the uncertainty in- the 'temperatures adopted from the (R-I) colour to be about 300°K. These uncertainties, along with the effect of composition changes(Scalo and Dlrich 1975) make it dangerous to' assign a mass solely from the position in the H-R diagram. Therefore the tracks are labeled mainly for ease of reference although I will be assuming that the stars do have the masses assigned to them. 95 The first conclusion to be drawn from Figure 9 is that all the stars observed appear to be in the double shell source phase of'evolution. This is in disagreement with the suggestion of Eggen(1972b) that the N stars are in the core helium ignition phase. In the double-shell source phase a star consists of a carbon-oxygen core •surrounded by a helium burning shell and still further out lies the hydrogen burning shell. Above this lies the outer convective envelope of the star. The two warmest stars in this sample lie fairly close to the tip of the 9 M<s> first giant branch so that it is not clear that tnese are double shell source stars as opposed to core helium ignition stars. However for the remaining discussion I will assume that they are in fact double shell source stars. The next"thing to note from this diagram is the fact that, except for the five stars -lying to the left of the 7 track all the stars* are bounded on the lower left by the onset of helium shell flashes* -No cool carbon star less massive than 7 M© is found in-the pre-helium shell flash phase of evolution. This strongly suggests that stars less massive than 7 II <g become cool carbon stars 'because of the onset of helium shell flashes. For stars more-massive than 7 MQ this fact is uncertain as no models have been constructed which are evolved to the stage of helium shell flashes. These stars could very well be post-helium shell flash objects as well. The exact mechanism by which the carbon is mixed to the 96 surface after the onset of the helium shell flashes is uncertain. Several different mechanisms have been suggested (Olrich and Scalo 1972; Scalo and Ulrich 1973; Ulrich 1973; Smith,Sackmann,and Despain 1973; Sackmann,Smith and Despain 1974; Iben 1975,1976). The basic idea is to bring hydrogen, carbon and helium into contact at high temperatures. It is possible that the individual mechanisms work more efficiently for certain mass ranges than for others. There exists an almost unique core mass-luminosity relationship for double shell source red giants (Paczynski 1971; Iben 1976). Knowing the absolute bolometric magnitude of a double shell source star allows one to assign a mass to the core, assuming that the core is non-rotating. It is interesting to calculate the core mass of the most luminous(bolometrically) star in this .sample. Using Iben's relationship, L/LQ = 6x10* (Mcore - 0.41) one finds a core mass of 1.73 . This is well above the Chandrasekhar limiting mass { 1.4M<9 ) which is the maximum mass for such a carbon-oxygen configuration. The spectra of stars 1-12 and 6-6 indicate that significant mixing has already occured in these stars. Since they are both above the theoretical upper mass limit for the core flash( 2.3MQ ) and if they are pre-helium shell flash objects this implies that the "hot-bottom" convective envelope hypothesis of Sealo,Despain, and Ulrich (1975) may be responsible for the mixing observed in these stars. These stars are well above the critcal luminosity for 97 this effect to occur. It is also worthwhile to comment on the very interesting star 4-9, number seven in Fiqure 9. This star exhibits an extremely high abundance of 13C so that it is presumably the most highly evolved object in this sample of seven stars in the sense that shell flashes have been occuring in this object for a significant period of time. As the temperature at the base of the convective envelope increases it becomes easier for 12C to form l3C and 14N by single and double proton captures respectively. If the temperature at the base of the convective envelope keeps rising it is possible that 4-9 could ba on its way to destroying its carbon star characteristics. 98 VI Summary In this thesis a catalogue of cool carbon stars in the Large Magellanic Cloud has been presented. The catalogue is expected to be complete to an I magnitude of about 13.5, the approximate limiting magnitude of the objective prism survey from which the- stars were identified. The stars were kindly identified by Dr. B.E. aesterlund from plates he obtained at the Uppsala Southern Station on Mount Stromlo. Finding charts and equatorial coordinates for the 309 stars which comprise the catalogue have been given. Such a catalogue should prove to be useful now that several large telescopes are operatioal in the southern hemisphere. • The fact that the distance to the Large Magellanic Cloud is well known allows many observations to be made which otherwise would not be possible. It is important to obtain as many accurate absolute magnitudes as possible for carbon stars as the data available now is quite sparse. Photometric observations on the VRI system of forty carbon stars, selected frcm the - catalogue, were made in order to investigate the photometric properties of carbon stars with known absolute magnitudes. Correlations between absolute visual magnitude and various photometric colours have been searched for but no significant results were found. The bulk of the stars investigated ' seem to form an empirical bright giant branch on the Mbol - V-R diagram. However this could be a selection effect as the photometric observations were restricted to a brighter than average qroup. Two mildly peculiar stars were 99 found in this sample of stars. These sere stars 1-12 and 6-6 in the catalogue. They are warm luminous stars which exhibit substantial amounts of 13C in their atmospheres. They also appear to lie 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 characteristics:"a higher than normal abundance of 13C, as defined by Bouigue (1954) and Gordon (1967). This was unexpected as this is proportionally a much larger number of stars than for carbon stars in our Galaxy. One star, 4-9, showed extreme J star characteristics. The most outstanding feature in the spectrum of 4-9 is the 13Ca*N band at ^6260. In many cases the- bands involving 13C are stronger than the corresponding iZC ones. The evolutionary status of carbon stars is not presently well understood.- It is useful to place the stars in a theoretical Hertzsprung-Russell diagram to aid in explaining their evolutionary development. Using the best available data for bolometric -corrections and using blackbody temperatures as effective temperatures as argued for by Scalo(1976) the stars were placed in a theoretical H-R diagram. Although the positions of the stars are a bit uncertain due to the effects of 100 composition changes and uncertainties in the derived temperatures, the cool carbon stars are almost certainly in the double shell source phase of evolution. In this phase the stars have two active burning shells, one of helium and one of hydrogen. It also.appears as though they are undergoing thermal pulses in the helium burning shell as described by Shwarzschild and Harm (1965).' In fact the stars less massive tuan seven solar masses seem to be bounded below by the onset of these helium shell flashes. It is guite possible that the helium shell flashes are the mechanism by which intermeriate mass stars become carbon stars(Iben 1975). The two mildly peculiar stars, 1-12 and 6-6, appear to be slightly more massive than seven solar masses. These stars may ba pre-helium shell flash objects although this point is uncertain as models have not yet been constructed which are detailed enough at this point in the star's evolution. Now that several large telescopes exist in the southern hemisphere a program of obtaining medium dispersion spectra of as many of these stars as possible should be started. Then it may be possible to devise a classification system in which the temperature,luminosity and abundance effects can be sorted out. Higher dispersion spectra should be obtained of some of the brighter objects to aid in unerstanding the evolutionary status of the cool carbon stars. 101 Bibliography, Bahng, L. 1966, in Colloquium on Late-Type Stars, ed. M. Hack (Trieste:Observatorio di Trieste), p. 255. Barnes, T.G. 1973, Ap. J. Suppl. Ser. No. 221, 25 , 369. Bartholdi, P., Evans, D.S., Mitchell, H.I., Silverberg, E.C., Sells, D.C., and Hiant, J.R. 1972 A.J., 77 , 756. Bessell, M.S., and Youngbom, L. 1972, Proc. Astr. Soc. Australia, 2 ,154. 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 ,40. De Vegt, C. 1974, Astr. 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, dissertation, University 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 published. Johnson, H.L. 1966, Ann. - Rev. Astr. 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. Mavridis, L.N. 1967, in Colloguium on Late-Type Stars, ed. M. Hack (Trieste:Observatorio di Trieste), p. 420. Mendoza, E.E. 1967, Bull. Tonantzintla y Tacubaya Obs., 3 , 305. Mendoza, E.E., and Johnson, H.L. 1965, Ap. J., 141 , 161. 102 Olsen, B.I., ana Richer, H.B. 1975, Ap. J., 200 , 88. Paczynski, B. 1970, Acta Astr., 20 , 47. Richer, H.B. 1971, Ap. J. , J.67 , 521. Richer, H.B. 1972, Ap. J. (Letters) , 172 , L63. i Richer, H.B. 1975, Ap. J., 197 , 611. Sackmann, I.J., Smith, R.L., and Despain, K.H. 1974, Ap. J., 187 , 555. Scalo, J.M. 1973, Ap. J., J86 , 967. Scalo, J.M. 1976, Ap. J.1, 206 , 474. Scalo, J.M., Despain, K.H., and Ulrich, R.K. 1975, Ap. J., 196 , 805. > Scalc,J.M., and Ulrich, R.K. 1975, Ap. J., 200 , 682. Schwarzschild, M. , and Harm, R. 1965, Ap. J., 145 ,496. Shane, CD. 1928, Lick Obs. Bull., "1.3 , 123. Smart, W.M. 1971, Textbook on Spherical Astronomy(5th ed.; Cambridge:Cambridge:University Press),p. 278. Smith, R.L. Sackmann, I.J. , and Despain, K. H. , 1973, in Explosive Nucleosynthesis, ed. D.N. Schramm and W.D. Arnett (Austin:University of Texas Press), p. 168. Ulrich, R.K. 1973, in Explosive Nuleosynthesis, ed. D.N. Schramm and M.D. Arnett(Austin:University of Texas Press) , p. 139. Ulrich, R.K., and Scalo, J.M. 1972, Ap. J.(Letters), 176 , L37. Ulrich, R.K., and Scalo, J.M. 1976, in preparation. Hallerstein, G. 1973, Ann. Rev. Astr. and Ap., H , 115. westerlund, B.E. 1964, in 1AU Symposium 20, The Galaxy and the Magellanic Clouds, ed. F.J. Kerr and A.8. Rodgers(Canberra: Australian Academy of Science), p. 239. Westerlund, B.E. 1972, Proc. 1st European Astronomical Meeting, ed. L.N. Mavridis. Wing, R.F. 1967, Ph.D. Dissertation, University of California, B erkely. 103 Yamashita, Y. 1972, Ann. Tokyo Astr. Obs., 2d Ser., Vol. 13 , No. 3. 

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