Three carbon-enhanced metal-poor dwarf stars from the SDSS - Chemical abundances from CO5BOLD 3D hydrodynamical model atmospheres

摘要

Context. The origin of carbon-enhanced metal-poorstars enriched with boths andrelements is highly debated. Detailed abundances of these types of starsare crucial to understand the nature of their progenitors. Aims. The aim of this investigation is to study indetail the abundances of SDSS J1349-0229, SDSSJ0912+0216 andSDSSJ1036+1212, three dwarf CEMP stars, selected from theSloan Digital Sky Survey. Methods. Using high resolution VLT/UVES spectra ()we determine abundances forLi, C, N, O, Na, Mg, Al, Ca, Sc,Ti, Cr, Mn, Fe, Co, Ni and 21neutron-capture elements. Wemade use of CO5BOLD 3D hydrodynamical modelatmospheres in the analysis of the carbon, nitrogen and oxygenabundances. NLTE corrections for C I and O Ilines were computed using the Kiel code. Results. We classify SDSSJ1349-0229 andSDSSJ0912+0216 as CEMP-r+s stars. SDSS J1036+1212 belongs tothe class CEMP-no/s, with enhanced Ba, but deficient Sr, of which it isthe third member discovered to date. Radial-velocity variations havebeen observed in SDSSJ1349-0229, providing evidence that itis a member of a binary system. Conclusions. The chemical composition of the threestars is generally compatible with mass transfer from an AGB companion.However, many details remain difficult to explain. Most notably ofthose are the abundance of Li at the level of the Spite plateau inSDSSJ1036+1212 and the large over-abundance of the pure r-processelement Eu in all three stars. Key words: stars: individual:SDSSJ1349-0229 - stars: individual: SDSSJ0912+0216- stars: individual: SDSSJ1036+1212 - stars: abundances -stars: AGB and post-AGB - stars: atmospheres