The chemical composition of R-stars

Zamora, O.; Abia, C.; Plez, B.; Domınguez, I.
Bibliographical reference

Memorie della Società Astronomica Italiana, v.77, p.973 (2006)

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2006
Number of authors
4
IAC number of authors
0
Citations
4
Refereed citations
3
Description
The preliminary results of the chemical analysis of a sample of 22 galactic R-stars with measured parallaxes are presented. We have derived the C/O and 12C/13C ratios, the average metallicity ([M/H]) and the Li abundances. We find that most of the stars have 12C/13C below ˜ 20 with no significant difference between cool and hot R-stars. The C/O ratio ranges between ˜ 1 to 2. We obtain a clear separation in the Li abundance between hot and cool R stars, with a mean value of log epsilon (Li) = +0.90 and log epsilon (Li) =-0.50, respectively. Cool stars are of near solar metallicity whereas hot stars show a larger spread, -0.5< [Fe/H] < +0.1. Concerning the possibility of s-element enhancements, we obtain [Rb/M] > 0 in seven hot stars and in three of them (R-hot) the analysis of the 5924 {Å} TcI line might be compatible with Tc detection. However, the detection of other s-element enhancements is necessary to elucidate the evolutionary stage of these carbon stars of which origin is still unknown.