Bibcode
Behara, N. T.; Bonifacio, P.; Ludwig, H.-G.; Sbordone, L.; González Hernández, J. I.; Caffau, E.
Bibliographical reference
Astronomy and Astrophysics, Volume 513, id.A72
Advertised on:
4
2010
Journal
Citations
84
Refereed citations
73
Description
Context. The origin of carbon-enhanced metal-poor stars enriched with
both s and r elements is highly debated. Detailed abundances of these
types of stars are crucial to understand the nature of their
progenitors. Aims: The aim of this investigation is to study in
detail the abundances of SDSS J1349-0229, SDSS J0912+0216 and SDSS
J1036+1212, three dwarf CEMP stars, selected from the Sloan Digital Sky
Survey. Methods: Using high resolution VLT/UVES spectra (R ~ 30
000) we determine abundances for Li, C, N, O, Na, Mg, Al, Ca, Sc, Ti,
Cr, Mn, Fe, Co, Ni and 21 neutron-capture elements. We made use of
CO5BOLD 3D hydrodynamical model atmospheres in the analysis
of the carbon, nitrogen and oxygen abundances. NLTE corrections for Ci
and Oi lines were computed using the Kiel code. Results: We
classify SDSS J1349-0229 and SDSS J0912+0216 as CEMP-r+s stars. SDSS
J1036+1212 belongs to the class CEMP-no/s, with enhanced Ba, but
deficient Sr, of which it is the third member discovered to date.
Radial-velocity variations have been observed in SDSS J1349-0229,
providing evidence that it is a member of a binary system.
Conclusions: The chemical composition of the three stars is generally
compatible with mass transfer from an AGB companion. However, many
details remain difficult to explain. Most notably of those are the
abundance of Li at the level of the Spite plateau in SDSS J1036+1212 and
the large over-abundance of the pure r-process element Eu in all three
stars.
Based on observations obtained with the ESO Very Large Telescope at
Paranal Observatory, Chile (programmes 078.D-0217 and 383.D-0927).