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Session 13 - Stellar Spectra.
Display session, Wednesday, January 07
Exhibit Hall,

[13.04] Neutron Capture Element Abundances in Galactic Halo Stars

D. L. Burris, J. J. Cowan (U. Oklahoma), C. A. Pilachowski, T. Armandroff (NOAO), C. Sneden (U. Texas)

New abundance results of the neutron capture (n-capture) elements (e.g. Ba, La, Eu, etc.) for 44 metal-poor Population II halo stars are presented. The Bond giants' echelle spectra analyzed were of resolution R 20,000 with S/N in the 100-200 range. The spectra were systematically analyzed so that direct star-to-star comparisons can be made. Isotopic hyper-fine splitting was considered in relative lines (e.g. Eu, Ba). The large sample size bridges the gap between analyses done on the old halo population (McWilliam et al 1995) and the younger Population I disk stars from the Woolf et al (1996) survey. At lower metallicites the abundance patterns appear to be correlated and the abundance pattern corresponds to the scaled solar system r-process signature. At higher metallicity, [Ba/Eu] trends can be attributed to the onset of the contribution of the s-process. Over the range of metallicity (-2.90<[Fe/H]<-0.86) there exist real star-to-star differences in the ratios of the [n-capture/Fe] abundances as well as in the actual spectra of the stars.

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