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R. S. French, C. Sneden (Univ. of Texas at Austin), J.J. Cowan (Univ. of Oklahoma), J.E. Lawler (Univ. of Wisconsin), F. Primas (ESO), T.C. Beers (Michigan State Univ.), J.W. Truran (Univ. of Chicago)
Abundances of the most massive stable elements (Os arrow Pb or 76 \leq Z \leq 82) in metal-poor stars can provide crucial information about the so-called ``third neutron-capture peak,'' and are critical to the radioactive-dating technique that uses unstable thorium and uranium as chronometers. As the relevant transitions occur in the UV and are inaccessable to ground-based telescopes, we have obtained high resolution (R ~q 30,000) UV spectra of 10 very metal-poor (--3.0 \leq [Fe/H] \leq --1.4) halo giants using the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope. Using iterative spectrum synthesis techniques, we derive abundances for some of these heavy elements. We compare our abundances to those predicted for very metal-poor stars based on a scaled solar system rapid-process (production in rapid neutron-capture synthesis events, such as occurs during supernovae explosions).
This research is supported by NASA STScI grant GO-08342 and NSF grants AST-9618364 to C.S. and AST-9618332 to J.J.C.