Bibcode
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
Citations
3
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.