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Originally published in Science Express on 2 June 2005
Science 15 July 2005:
Vol. 309. no. 5733, pp. 451 - 453
DOI: 10.1126/science.1112997
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Reports

The First Chemical Enrichment in the Universe and the Formation of Hyper Metal-Poor Stars

Nobuyuki Iwamoto,1 Hideyuki Umeda,2 Nozomu Tominaga,2 Ken'ichi Nomoto,2* Keiichi Maeda3

The recent discovery of a hyper–metal-poor (HMP) star, with a metallicity Fe/H smaller than 1/100,000 of the solar ratio, together with one earlier HMP star, has raised a challenging question whether these HMP stars are the actual first-generation, low-mass stars of the universe. We argue that these HMP stars are second-generation stars formed from gases that were chemically enriched by the first-generation supernovae. The key to this solution is the very unusual abundance patterns of these HMP stars and the similarities and differences between them. We can reproduce these abundance features with core-collapse "faint" supernova models that include extensive matter mixing and fallback during explosions.

1 Nuclear Data Center, Japan Atomic Energy Research Institute, Ibaraki 319-1195, Japan.
2 Department of Astronomy, School of Science, University of Tokyo, Tokyo 113-0033, Japan.
3 Department of Earth Science and Astronomy, College of Arts and Sciences, University of Tokyo, Tokyo 153-8902, Japan.

* To whom correspondence should be addressed. E-mail: nomoto{at}astron.s.u-tokyo.ac.jp

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Science. ISSN 0036-8075 (print), 1095-9203 (online)