EDP Sciences
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Volume 402, Number 3, May II 2003
First Science with the ODIN satellite
Page(s) 1061 - 1071
Section Formation and evolution of planetary systems
DOI http://dx.doi.org/10.1051/0004-6361:20030209

A&A 402, 1061-1071 (2003)
DOI: 10.1051/0004-6361:20030209

Spectroscopic analysis of two CH subgiant stars: HD 50264 and HD 87080

C. B. Pereira1, 2 and S. Junqueira1

1  Observatório Nacional-MCT, Rua José Cristino, 77, CEP 20921-400, São Cristóvão, Rio de Janeiro-RJ, Brazil
2  CENTRA, Instituto Superior Técnico, Avenida Rovisco Pais 1, 1096, Lisboa, Portugal

(Received 23 April 2002 / Accepted 17 January 2003 )

We present the abundance pattern of two CH subgiant stars HD 50264 and HD 87080 based on high-resolution optical spectra. We also determined the spectroscopic stellar atmospheric parameters, temperature and microturbulent velocity as well as stellar surface gravity from a solution of excitation and ionization equilibria of Fe I and Fe II lines under the assumption of local thermodynamic equilibrium. The abundance analysis reveals HD 50264 with a metallicity of $\rm [Fe/H]=-0.34$ and HD 87080 with a metallicity of $\rm [Fe/H]=-0.51$.

We compare the abundance pattern with abundances of disk stars and also with other stars of the same class. We found that iron group, $\alpha$-elements, manganese, as well as sodium and aluminum of HD 50264 and HD 87080 follow the abundance pattern of the disk stars. The heavy-element abundance pattern of both stars shows enhancements by a factor of 4-6 with respect to the sun. By heavy-element we mean the elements that have been synthesized by neutron capture, such as barium, yttrium and zirconium. We also discuss the abundances of the s-process elements and compare our results with other binary systems that display enrichment due to neutron-capture reactions, through several diagrams involving the index [hs/ls] and [s/Fe], the metallicity and [C/Fe] ratio. We compare the observed abundance of the heavy elements with theoretical nucleosynthesis calculations. This shows that the s-process are best fit by models in which the seed nuclei are exposed to single neutron irradiation and with a neutron exposure of $\tau=0.9$ and $\tau=1.0$ respectively for HD 50264 and HD 87080. We also use the [Rb/Zr] ratio in order to investigate how this ratio behaves versus metallicity for other binary systems, including HD 50264 and HD 87080 that are s-process enriched.

Key words: stars: chemically peculiar -- stars: abundances

Offprint request: C. B. Pereira, claudio@on.br

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