Evolution of heavy-element abundances as a constraint on sites for neutron-capture nucleosynthesis

Abstract

Observed heavy-element abundance ratios in the halo and the disk are compared with one-zone models of galactic chemical evolution. These comparisons provide useful insight into the kinds of stellar environments responsible for r- and s-process nucleosynthesis. The growth of r-process material appears to be associated with the ejection rate of material from massive stars. Low-mass Type II supernovae are slightly favored if the r-process is primary. The growth of s-process material is consistent with production in intermediate-mass stars. The yields for both the s- and the r-process, however, appear to require a neutron source which does not depend upon initial metallicity.