First Stars. III. A detailed elemental abundance study of four extremely metal-poor giant stars *,**
Observatoire de Paris-Meudon, GEPI, 92195 Meudon Cedex, France
2 GRAAL, Université de Montpellier II, 34095 Montpellier Cedex 05, France
3 Department of Physics & Astronomy, Michigan State University, East Lansing, MI 48824, USA
4 IAG, Universidade de São Paulo, Departamento de Astronomia, CP 3386, 01060-970 São Paulo, Brazil
5 Astronomical Observatory, NBIfAFG, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
6 Istituto Nazionale di Astrofisica - Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, 34131 Trieste, Italy
7 Lund Observatory, Box 43, 221 00 Lund, Sweden
8 European Southern Observatory (ESO), Karl-Schwarschild-Str. 2, 85749 Garching b. München, Germany
Corresponding author: P. François, Patrick.Francois@obspm.fr
Accepted: 21 March 2003
This paper reports detailed abundance analyses for four extremely metal-poor (XMP) giant stars with , based on high-resolution, high- spectra from the ESO VLT (Kueyen/UVES) and LTE model atmosphere calculations. The derived [ α/Fe] ratios in our sample exhibit a small dispersion, confirming previous findings in the literature, i.e. a constant overabundance of the α-elements with a very small (if any) dependence on [Fe/H]. In particular, the very small scatter we determine for [Si/Fe] suggests that this element shows a constant overabundance at very low metallicity, a conclusion which could not have been derived from the widely scattered [Si/Fe] values reported in the literature for less metal-poor stars. For the iron-peak elements, our precise abundances for the four XMP stars in our sample confirm the decreasing trend of Cr and Mn with decreasing [Fe/H], as well as the increasing trend for Co and the absence of any trend for Sc and Ni. In contrast to the significant spread of the ratios [Sr/Fe] and [Ba/Fe], we find [Sr/Ba] in our sample to be roughly solar, with a much lower dispersion than previously found for stars in the range .
Key words: stars: abundances / stars: Population II / Galaxy: abundances / Galaxy: halo / nuclear reactions, nucleosynthesis, abundances
Based on observations made with the ESO Very Large Telescope at Paranal Observatory, Chile (Large Programme ID 165.N-0276(A)).
© ESO, 2003