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Quantitative analysis of carbon isotopic ratios in carbon stars
III. 26 J-type carbon stars including 5 silicate carbon stars
K. Ohnaka * 1,2 and
T. Tsuji 1
Received 4 January 1999 / Accepted 18 February 1999
We present the result of a quantitative analysis of ratios in 26 J-type carbon stars. The ratios are determined from lines of the CN red system around 8000 Å, using the iso-intensity method and line-blanketed model atmospheres.
The average of ratios in the 26 stars is (standard deviation). All the stars studied, except for two stars, have ratios smaller than 10. ratios as low as , 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 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 ratios among the stars studied in the present work. This result implies that the mechanism responsible for low ratios in silicate carbon stars might be the same with that operating in other J-type carbon stars. In other words, ratios in silicate carbon stars have turned out to give few clues to identify the mechanism responsible for their formation.
Key words: stars: abundances stars: carbon stars: fundamental parameters stars: AGB and post-AGB
Send offprint requests to: K. Ohnaka (Technische Universität Berlin), (email@example.com.TU-Berlin.de)
Online publication: April 12, 1999