Abstract
We derive accurate relative abundances of elements in very metal-poor stars of high space motion from new high-resolution spectra. Our abundance results have several implications for nucleosynthesis in the collapsing gas of the galactic halo. We rule out the possibility of synthesis by supermassive objects, or by a single event whose products subsequently were diluted. Our abundance results for the elements through the iron peak support explosive nucleosynthesis with a constant ratio of the products of carbon-, oxygen-, and silicon-burning at all (Fe/H), and with low values of the neutron excess at (Fe/H)=-1.5, consistent with helium burning but not hydrostatic carbon burning as the preceding stage of stellar evolution. The relative abundances of the s-process elements show the predicted aging effect, decreasing in proportion to the iron-peak elements as (Fe/H) decreases. The large values derived for the average number of neutron captures at low (Fe/H) argue against /sup 22/Ne as the source of s-process neutrons. The rapid rise of the proportion of s-process elements to the solar-system value at (Fe/H)=-1.0 implies that objects of greater than 5 M/sub sun/ must have been responsible for s-process element production when values of (Fe/H) were low. (AIP)
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