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Chemical Abundance Patterns of Extremely Metal-Poor Stars with [Fe/H]$\lesssim -3.5$

Published online by Cambridge University Press:  23 December 2005

W. Aoki ,
T. C. Beers ,
N. Christlieb ,
A. Frebel ,
J. E. Norris ,
S. Honda ,
M. Takada-Hidai ,
M. Asplund ,
H. Ando  and
S. G. Ryan
...Show all authors
W. Aoki
Affiliation:
National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo, 181-8588, Japan email: aoki.wako@nao.ac.jp
T. C. Beers
Affiliation:
Department of Physics and Astronomy and JINA: Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, MI 48824, USA
N. Christlieb
Affiliation:
Hamburger Sternwarte, University of Hamburg, Gojenbergsweg 112, D-21029 Hamburg, Germany
A. Frebel
Affiliation:
Research School of Astronomy and Astrophysics, Mount Stromlo Observatory, Cotter Road, Weston, ACT 2611, Australia
J. E. Norris
Affiliation:
Research School of Astronomy and Astrophysics, Mount Stromlo Observatory, Cotter Road, Weston, ACT 2611, Australia
S. Honda
Affiliation:
National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo, 181-8588, Japan email: aoki.wako@nao.ac.jp
M. Takada-Hidai
Affiliation:
Liberal Arts Education Center, Tokai University, 1117 Kitakaname, Hiratsuka-shi, Kanagawa 259-1292, Japan
M. Asplund
Affiliation:
Research School of Astronomy and Astrophysics, Mount Stromlo Observatory, Cotter Road, Weston, ACT 2611, Australia
H. Ando
Affiliation:
National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo, 181-8588, Japan email: aoki.wako@nao.ac.jp
S. G. Ryan
Affiliation:
Department of Physics and Astronomy, Open University, Walton Hall, Milton Keynes MK76AA, UK
S. Tsangarides
Affiliation:
Department of Physics and Astronomy, Open University, Walton Hall, Milton Keynes MK76AA, UK
K. Nomoto
Affiliation:
Department of Astronomy, School of Science, University of Tokyo, Tokyo 113-0033, Japan
M. Y. Fujimoto
Affiliation:
Department of Physics, Hokkaido University, Sapporo 060-0810, Japan
T. Kajino
Affiliation:
National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo, 181-8588, Japan email: aoki.wako@nao.ac.jp
Y. Yoshii
Affiliation:
Institute of Astronomy, School of Science, University of Tokyo, Mitaka, Tokyo 181-0015, Japan
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Abstract

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We present preliminary results on the chemical abundance patterns of extremely metal-poor stars obtained during an ongoing observing program with Subaru/HDS. High-resolution, high signal-to-noise spectra have been obtained for 14 stars with [Fe/H]$\lesssim -3$. Five of them exhibit clear overabundances of carbon, a remarkable characteristic found only in the most metal-poor range. One of the carbon-rich stars, HE 1327–2326, has [Fe/H]$_{\rm NLTE}=-5.4$, the lowest Fe abundance known. No stars with ${-}5\,{<}\,$[Fe/H]$\,{<}\,{-}4$ have yet been found in our program, suggesting that quite different enrichment processes were responsible for stars with [Fe/H]$\,{<}\,{-}5$ and [Fe/H]$\,{>}\,{-}4$. While neutron-capture elements are deficient in most of our stars, one star (BS 16550–087) exhibits large enhancements of its light neutron-capture elements (Sr, Y and Zr), providing a strong constraint on models for the production of such elements in the very early Galaxy.

Keywords

Stars: abundancesstars: Population IIGalaxy: halo

Footnotes

Based on data collected with the Subaru telescope, which is operated by the National Astronomical Observatory of Japan.