ULTRAMETAL-POOR HALO STARS - THE REMARKABLE SPECTRUM OF CS-22892-052

The star CS 22892-052, discovered in the HK Objective-Prism survey of the southern Galactic halo, is extremely weak-lined at low resolution. At higher resolution, features of very heavy neutron-capture elements and CH dominate the spectrum. An abundance analysis reveals that this star is indeed very metal-poor: [Fe-peak/H] approximately -3.1. The a lpha elements Mg, Ca, and Ti are enhanced by factors typical for halo stars, [alpha/Fe] congruent-to + 0.4. The neutron-capture elements are strongly overabundant: + 0.3 < [n-capture/Fe] < + 1.8 in the range 38 less-than-or-equal-to Z less-than-or-equal-to 68, with the enhancemen ts generally growing with increasing Z. The ratio [C/Fe] approximately + 1 also is much larger than in any other known star of this metallic ity range. The total n-capture element distribution is well represente d by an r-process nucleosynthesis yield. This star provides the cleare st evidence for element enrichment from '' local '' supernovae nucleos ynthesis events in an unmixed early Galactic halo.