Oxygen overabundance in the extremely iron-poor star CS 29498-043

An abundance analysis for the carbon-enhanced, extremely iron-poor ([Fe/H] similar to -3.5) star CS 29498-043 has been obtained using new high-resolution, high signal-to-noise ratio spectra from the Subaru Telescope. The [O (I)] forbidden line at 6300 Angstrom and the O (I) triplet feature at 7771-7776 A 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 alpha-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.