BARIUM ABUNDANCES IN EXTREMELY METAL-POOR STARS

New, improved, barium abundances for 33 extremely metal-poor halo star s from the 1995 sample of McWilliam et al. have been computed. The mea n [Ba/Eu] ratio for stars with [Fe/H] less than or equal to -2.4 is -0 .69 +/- 0.06 dex, consistent with pure r-process nucleosynthesis withi n the measurement uncertainties. Although the [Sr/Fe] and [Ba/Fe] abun dance ratios span a range of 2.6 dex, the mean values are approximatel y constant with [Fe/H]. This is consistent with a model of chemical ev olution in which the parent clouds were enriched by small numbers of s upernova events. In this model, the decreasing heavy-element dispersio n with increasing [Fe/H] is simply due to the averaging of element yie lds from many supernovae at higher [Fe/H]; however, it is necessary to increase the number of extremely metal-poor stars known in order to c onfirm this picture. In addition to the random Sr component from the r -process, the [Sr/Ba] ratios indicate that there is a second, also ran dom, source of Sr from an as yet unidentified nucleosynthesis site.