Lithium Abundances of Extremely Metal-Poor Turn-off Stars

We have determined Li abundances for eleven metal-poor turn-off stars, among which eight have [Fe/H] < −3, based on LTE analyses of high-resolution spectra obtained with the HDS on the Subaru telescope. The Li abundances for four of these eight stars are determined for the first time by this study. Effective temperatures are determined by a profile analysis of Hα and Hβ. While seven stars have Li abundances as high as the Spite Plateau value, the remaining four objects with [Fe/H] < −3 have A(Li) = log(Li/H)+12 . 2.0, confirming the existence of extremely metal-poor turn-off stars having low Li abundances, as reported by previous work. The average of the Li abundances for stars with [Fe/H]< −3 is lower by 0.2 dex than that of the stars with higher metallicity. No clear constraint on the metallicity dependence or scatter of the Li abundances is derived from our measurements for the stars with [Fe/H]< −3. Correlations of the Li abundance with effective temperatures, with abundances of Na, Mg and Sr, and with the kinematical properties are investigated, but no clear correlation is seen in the extremely metal-poor star sample. Subject headings: nuclear reactions, nucleosynthesis, abundances – stars: abundances –stars: Population II National Astronomical Observatory, Mitaka, Tokyo, 181-8588 Japan; email: [email protected] Department of Astronomical Science, The Graduate University of Advanced Studies, Mitaka, Tokyo, 181-8588 Japan Department of Physics and Astronomy, Uppsala University, Box 515, 751-20 Uppsala, Sweden; email: [email protected] Department of Physics and Astronomy, CSCE: Center for the Study of Cosmic Evolution, and JINA: Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, MI 48824-1116; email: [email protected] University of Heidelberg, ZAH, Landessternwarte Königstuhl 12, D-69117 Heidelberg, Germany, [email protected] Present address: Department of Physics, Kyoto University, Oiwake-cho, Kitashirakawa, Sakyo-ku, Kyoto 6068502, Japan; email:[email protected] Centre for Astrophysics Research, STRI and School of Physics, Astronomy and Mathematics, University of Hertfordshire, College Lane, Hatfield AL10 9AB, United Kingdom; email: [email protected] Research School of Astronomy and Astrophysics, The Australian National University, Mount Stromlo Observatory, Cotter Road, Weston, ACT 2611, Australia; email: [email protected], [email protected] INAF-Osservatorio Astronomico di Torino, Italy