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Issue A&A
Volume 429, Number 3, January III 2005
Page(s) 1031 - 1042
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20040415



A&A 429, 1031-1042 (2005)
DOI: 10.1051/0004-6361:20040415

New analysis of the two carbon-rich stars CS 22948-27 and CS 29497-34: Binarity and neutron capture elements

B. Barbuy1, M. Spite2, F. Spite2, V. Hill2, R. Cayrel3, B. Plez4 and P. Petitjean5

1  Universidade de São Paulo, Rua do Matão 1226, São Paulo 05508-900, Brazil
    e-mail: barbuy@astro.iag.usp.br
2  Observatoire de Paris-Meudon, GEPI, URM 8633 du CNRS, 92195 Meudon Cedex, France
3  Observatoire de Paris, GEPI, 61 Av. de l'Observatoire, 75014 Paris, France
4  GRAAL cc72, Université de Montpellier II, 34095 Montpellier Cedex 5, France
5  Institut d'Astrophysique, 98bis Bd. Arago, 75014 Paris, France

(Received 9 March 2004 / Accepted 27 August 2004 )

Abstract
We have carried out a new determination of abundances in the very metal-poor CH/CN strong stars CS 22948-27 and CS 29497-34, using high-resolution spectra obtained with the HARPS spectrograph at the 3.6 m telescope of ESO, La Silla, that covers the range $\lambda\lambda$ 4000-6900 Å at a resolution of  $R = 100\,000$. Both stars are found to be long period binaries. It is confirmed that the abundance patterns show an enhancement of the $\alpha$-elements (like Mg, Ca), of the proton capture elements (like Na and Al) and a strong enrichment in "r" and "s" process elements, where the s-enrichment is probably due to a mass transfer episode from a companion in its AGB phase. The possible origins of the abundance pattern and especially of the strong enhancement of both "s" and "r" elements are discussed.


Key words: stars: abundances -- stars: population II -- stars: carbon -- stars: binaries: spectroscopic -- Galaxy: bulge -- nuclear reactions, nucleosynthesis, abundances

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© ESO 2005


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