Quantitative analysis of carbon isotopic ratios in carbon stars. III. 26 J-type carbon stars including 5 silicate carbon stars

Details Quantitative analysis of carbon isotopic ratios in carbon stars. III. 26 J-type carbon stars including 5 silicate carbon stars Quantitative analysis of carbon isotopic ratios in carbon stars. III. 26 J-type carbon stars including 5 silicate carbon stars

May 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999a%26a...345..233o&link_type=abstract

Astronomy and Astrophysics, v.345, p.233-243 (1999)

Astronomy and Astrophysics

Astrophysics

27

Stars: Abundances, Stars: Carbon, Stars: Fundamental Parameters, Stars: Agb And Post-Agb

Scientific paper

We present the result of a quantitative analysis of (12C/({13)) C} ratios in 26 J-type carbon stars. The (12C/({13)) C} ratios are determined from lines of the CN red system around 8000 Angstroms, using the iso-intensity method and line-blanketed model atmospheres. The average of (12C/({13)) C}\ ratios in the 26 stars is 4.7 +/- 2.8 (standard deviation). All the stars studied, except for two stars, have (12C/({13)) C}\ ratios smaller than 10. (12C/({13)) C}\ ratios as low as 1 ~ 2, which are lower than the value at the equilibrium of the CN-cycle, are found for a significant fraction of our sample, suggesting the operation of non-equilibrium nuclear processes. For several stars previously analyzed by other authors, our result shows fair agreement. The serious disagreement of (12C/({13)) C}\ ratios, which we reported for N-type carbon stars in our preceding paper, is not found for J-type carbon stars. Five silicate carbon stars in our sample show no peculiar (12C/({13)) C} ratios among the stars studied in the present work. This result implies that the mechanism responsible for low (12C/({13)) C}\ ratios in silicate carbon stars might be the same with that operating in other J-type carbon stars. In other words, (12C/({13)) C}\ ratios in silicate carbon stars have turned out to give few clues to identify the mechanism responsible for their formation.

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