Chemical Evolution of Heavy Elements in the Early Galaxy: Implications for Stellar Sources

An overview of the sources for heavy elements in the early Galaxy is given. It is shown that observations of abundances in metal-poor stars can be used along with a basic understanding of stellar models to guide the search for the source of the heavy r-process nuclei (r-nuclei). Observations show that this source produces very little of the elements from C through Zn including Fe. This strongly suggests that O-Ne-Mg core-collapse supernovae (SNe) from progenitors of ∼ 8–11M⊙ are the source for the heavy r-nuclei. It is shown that a two-component model based on the abundances of Fe (from Fe core-collapse SNe) and Eu (from O-Ne-Mg core-collapse SNe) gives very good quantitative predictions for the abundances of all the other elements in metal-poor stars.