ar X iv : a st ro - p h / 04 02 58 5 v 1 2 5 Fe b 20 04 Oxygen Overabundance in the Extremely Iron - Poor Star CS 29498

An abundance analysis for the carbon-enhanced, extremely iron-poor ([Fe/H]∼ −3.5) star CS 29498–043 has been obtained using new high-resolution, high signalto-noise spectra from the Subaru Telescope. The [O I] forbidden line at 6300 Å and the O I triplet feature at 7771-7776 Å are both clearly detected. The overabundance of oxygen is significant ([O/Fe]> 2). In addition, Na, Co, and Ni abundances have been newly measured. The abundance pattern from C to Ni of this object is quite similar to that of CS 22949–037, another extremely metal-poor star with large excesses of C, N, O, and the α-elements. The abundance patterns of these two stars suggest the existence of supernovae progenitors that ejected relatively little material from their iron cores during the very early era of nucleosynthesis in the Galaxy. The metallicity in these objects, when one includes the elements C, N, and O in the tally of total metals, is not as low as in the most metal-poor stars, suggesting the existence of quite different formation processes for these iron-deficient objects than pertain to the bulk of other metal-deficient stars. Subject headings: nuclear reactions, nucleosynthesis, abundances — stars: abundances — stars: carbon — stars: individual (CS 29498–043) — stars: Population II National Astronomical Observatory, Mitaka, Tokyo, 181-8588 Japan; email: [email protected], [email protected] Research School of Astronomy and Astrophysics, The Australian National University, Mount Stromlo Observatory, Cotter Road, Weston, ACT 2611, Australia; email: [email protected] Department of Physics and Astronomy, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK; email: [email protected], [email protected] Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824-1116; email: [email protected] Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany; [email protected] Based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.