J/A+A/310/933 C isotopic ratio in N- and SC-type stars (Ohnaka+, 1996)
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 1996A&A...310..933O (SIMBAD/NED BibCode)
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 12C/13C 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
12C/13C 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 12C/13C 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 12C/13C ratios less than 40,
and the number of stars which have 12C/13C 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, 12C/13C ratios mostly larger than 40 in
N-type carbon stars. The average of 12C/13C 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 12C/13C ratios
larger than 10, while only three of them turn out to be 13C-rich.
This is in contrast with the earlier classification based on low
resolution spectra which classified them as J-type, that is,
13C-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 12C/13C ratios are partly
consistent with the scenario in which M giants evolve through SC-type
to N-type carbon stars, as 12C 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 1972AnTok..13..169Y
Yamashita Y., 1975, Ann. Tokyo Astr. Obs. 2nd Ser. 15, 47
=1975AnTok..15...47Y 1975AnTok..15...47Y
(End) Patricia Bauer [CDS] 26-Mar-1996