Heavy elements in globular clusters and dwarf galaxies as probes of the origin of r-process elements

Abstract

Chemical abundances of very metal-poor stars record the nucleosynthesis products in the early Galaxy. Previous observational studies have revealed that the r-process is the dominant source of neutron-capture elements in extremely metal-poor stars, but the total amount of neutron-capture elements relative to lighter elements (e.g. Fe) shows large star-to-star scatter. These features are key to understanding the astrophysical sites of the r-process as well as the formation of stellar systems including extremely metal-poor stars. Such abundance studies for neutron-capture elements have been extended to metal-poor stars in globular clusters and dwarf galaxies around the Milky Way, in addition to field halo stars. We investigated the abundance ratios of neutron-capture elements for an extremely metal-poor star in the Sextans dwarf galaxy for which a significant excess of Ba was detected by a previous study, and found that the origin of heavy elements in this object is the sprocess. Although the sample size is still small, no r-process enhanced star has been found in dwarf galaxies at such low metallicity, in contrast to the Galactic halo. From ourmeasurements of neutroncapture elements in three very metal-poor globular clusters, we confirmed star-to-star scatter of Eu abundance ratios in M15, but found that these clusters are almost homogeneously enriched in lighter neutron-capture elements.