First enrichment of r-process elements in our Galaxy Original Research Article

Observed large scatters in Eu, Ba, and Sr abundances of metal-poor stars provide clues to determine the site(s) of r-process. In particular, our observation using Subaru HDS gives sub-solar values of [Eu/Fe] for three extremely metal-poor stars. Using an inhomogeneous chemical evolution model, we show that the dominant source of Eu to be the low-mass end of the supernova mass range to account for the observation. On the other hand, scatters in [Sr/Ba] suggest existence of “weak” r-process, which produces lighter nuclei. We also discuss the yield of weak r-process, using new data of Pd abundances.