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J/A+A/310/933       C isotopic ratio in N- and SC-type stars (Ohnaka+, 1996)
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Quantitative analysis of carbon isotopic ratios in carbon stars.
I. 62 N-type and 15 SC-type carbon stars.
      Ohnaka K., Tsuji T.
     <Astron. Astrophys. 310, 933 (1996)>
     =1996A&A...310..933O      (SIMBAD/NED BibCode)
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ADC_Keywords: Stars, carbon ; Photometry, CCD
Keywords:  stars: abundances - stars: atmospheres - stars: carbon -
           stars: fundamental parameters - stars: evolution -
           stars: AGB and post-AGB

Description:
    We present a result of quantitative analysis of ^12^C/^13^C ratios in
    62 N-type and 15 SC-type carbon stars. By the use of CCD as a detector
    we can obtain spectra of resolution ~20,000 with enough
    signal-to-noise ratios for a large number of carbon stars, for which
    ^12^C/^13^C ratios have not yet been derived. Carbon isotopic ratios
    are determined from lines of the CN red system around 8000A, based on
    the iso-intensity method and line-blanketed model atmospheres. The
    average of ^12^C/^13^C ratios in 62 N-type carbon stars is found to be
    27+/-11 (standard deviation). The majority of the N-type carbon stars
    studied (about 85%) are found to have ^12^C/^13^C ratios less than 40,
    and the number of stars which have ^12^C/^13^C ratios larger than 40
    is found to be relatively small. This result shows a marked contrast
    to some of the previous results that have shown the opposite
    distribution, namely, ^12^C/^13^C ratios mostly larger than 40 in
    N-type carbon stars. The average of ^12^C/^13^C ratios in 15 SC-type
    carbon stars is found to be 22+/-14 (standard deviation). Most of the
    SC-type carbon stars studied are found to have ^12^C/^13^C ratios
    larger than 10, while only three of them turn out to be ^13^C-rich.
    This is in contrast with the earlier classification based on low
    resolution spectra which classified them as J-type, that is,
    ^13^C-rich. The earlier temperature scale which classified SC-type
    carbon stars as the latest (C8-9) based on their strong NaI D lines
    can not be necessarily justified. The strong NaI D lines of SC stars
    should be attributed to the peculiar atmospheric structure due to C/O
    ratios very near to unity. The resulting ^12^C/^13^C ratios are partly
    consistent with the scenario in which M giants evolve through SC-type
    to N-type carbon stars, as ^12^C produced during the helium shell
    flash is added to the envelope.

File Summary:
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  FileName      Lrecl  Records   Explanations
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ReadMe             80        .   This file
table1             63      135   Summary of the observations of 66 N-type
                                  carbon stars
table1.tex         78      202   LaTeX version of table1
table2             62       38   Summary of the observations of 19 SC-type
                                  carbon stars
table2.tex         72       73   LaTex version of table2
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Byte-by-byte Description of file: table1 table2
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   Bytes Format Units   Label     Explanations
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   2-  5  I4    ---     GCCGCS    ? Designation in "A General Catalogue of Cool
                                   Galactic Carbon Stars", Stephenson (1989)
                                   (Catalogue <III/156>)
   7- 10  I4    ---     CCCS      ? Designation in "A General Catalogue of Cool
                                   Carbon Stars", Stephenson (1973)
      11  A1    ---   n_CCCS      [)] A ')' indicates that the designation is in
                                   "A General Catalog of S stars",
                                   Stephenson (1976) (Catalogue <III/168>)
  14- 23  A10   ---     Name      Star Name
  25- 31  A7    ---     C-Class   C-Classification, Yamashita (1972, 1975)
  33- 37  F5.2  mag     Vmag      V magnitude or lowest V magnitude if interval
      39  A1    ---   n_Vmag      [-] A '-' indicates an interval of magnitudes
      40  A1    ---   l_Vmag2     Limit flag on Vmag2
  41- 45  F5.2  mag     Vmag2     ? Upper V magnitude if interval
  48- 58  A11   ---     Obs       Date of observations for two wavelength
  60- 63  I4    ---     S/N       Signal-to-noise ratio
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References:
   Stephenson C.B., 1973, Publ. Warner and Swasey Obs. 1, No.4
   Stephenson C.B., 1976, Publ. Warner and Swasey Obs. 2, No.2
     =Catalogue <III/168>
   Stephenson C.B., 1989, Publ. Warner and Swasey Obs. 3, No.2
     =Catalogue <III/156>
   Yamashita Y., 1972, Ann. Tokyo Astr. Obs. 2nd Ser. 13, 169
     =1972AnTok..13..169Y
   Yamashita Y., 1975, Ann. Tokyo Astr. Obs. 2nd Ser. 15, 47
     =1975AnTok..15...47Y
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(End)                                         Patricia Bauer [CDS]   26-Mar-1996