AAS 201st Meeting, January, 2003
Session 17. Stellar Evolution and Metal-Poor Stars
Poster, Monday, January 6, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[17.15] Discovery of a Lead-Enriched Blue Metal-Poor Field Star

C. Sneden (U. Texas, Austin; Carnegie Obs.), G. W. Preston (Carnegie Obs.), J. J. Cowan (U. Oklahoma)

We have obtained new high resolution spectra of several blue metal-poor (BMP) stars of the Galactic field halo population. Such stars lie on the main sequence but are 500-1000~K warmer than the position of the metal-poor turnoff; more than half of them are binaries (Preston & Sneden 2000, AJ, 120, 1014). Of our 10 BMP program stars, six are very metal-poor ([Fe/H]~~ --2.1). Of these six, three are known binaries, and three have constant radial velocities. Our abundance analysis reveals significant differences between the binaries and the non-variables: all of the binaries have substantial overabundances of carbon and heavy elements easily synthesized in slow neutron-capture nucleosynthesis (the s-process): <[C/Fe]>~= +1.9, <[Sr/Fe]>~= +1.1, and <[Ba/Fe]>~= +1.4. No enhancements of these elements are seen in the constant velocity stars. Thus the BMP metal-poor binaries must have gained their peculiar abundances via mass transfer during the AGB phases of their companions, which now should be compact objects.

One of the BMP binaries, CS~29497-030, exhibits a strong line of Pb~I at 4057~Å. The derived [Pb/Fe] = +3.7 is the largest lead overabundance reported to date in s-process-enriched stars. The relative [Pb/(Ba or Sr)] abundance ratios are consistent with two other recently discovered very lead-rich stars (van Eck et al. 2001, Nature, 412, 793; Carretta et al. 2002, AJ, 124, 481).

This research has been supported by NSF grants AST-9987162 to C.S. and AST-9986974 to J.J.C.

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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.