Spectroscopic analysis of two CH subgiant stars: HD 50264 and HD 87080 *,**
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
Corresponding author: C. B. Pereira, claudio@on.br
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 
and HD 87080 with a metallicity
of 
.
We compare the abundance pattern with abundances of disk stars
and also with other stars of the same class. We found that iron group,
α-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 
and 
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
© ESO, 2003