Ther‐Process in the Early Galaxy

We report Sr, Pd, and Ag abundances for a sample of metal-poor field giants and analyze a larger sample of Y, Zr, and Ba abundances. The [Y/Zr] and [Pd/Ag] abundance ratios are similar to those measured for the r -process-rich stars CS 22892-052 and CS 31082-001. The [Pd/Ag] ratio is larger than predicted from the solar system r -process abundances. The constant [Y/Zr] and [Sr/Y] values in the field stars place strong limits on the contributions of the weak s -process and the main s -process to the light neutron-capture elements. Stars in the globular cluster M15 possess lower [Y/Zr] values than the field stars. There is a large dispersion in [Y/Ba]. Because the r -process is responsible for the production of the heavy elements in the early Galaxy, these dispersions require varying light-to-heavy ratios in r -process yields.