Astronomy and Astrophysics – Astrophysics
Scientific paper
May 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003a%26a...402.1061p&link_type=abstract
Astronomy and Astrophysics, v.402, p.1061-1071 (2003)
Astronomy and Astrophysics
Astrophysics
12
Stars: Chemically Peculiar, Stars: Abundances
Scientific paper
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 [Fe/H]=-0.34 and HD 87080 with a metallicity of [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.
Based on observations made with the 1.52 m telescope at the European Southern Observatory (La Silla, Chile) under the agreement with the Observatório Nacional, Brazil.
Tables 1 and 2 are only available in electronic form at http://www.edpsciences.org
Junqueira Selma
Pereira Claudio Bastos
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