Formation of the Abundance Boundaries of the Heavier Neutron-capture Elements in Metal-poor Stars

TL;DR

This paper explores how the upper and lower boundaries of r-process element abundance ratios in metal-poor stars are formed, revealing the roles of single r-process events and supernovae in early Galactic chemical evolution.

Contribution

It provides a new understanding of how the abundance boundaries of heavy neutron-capture elements are established in metal-poor stars.

Findings

Upper [r/Fe] limits are mainly due to single r-process events.

Lower [r/Fe] limits are mainly due to single SN II events ejecting primary Fe.

The study links abundance boundaries to specific astrophysical pollution events.

Abstract

The abundance scatter of heavier r-process elements (Z > 56) relative to Fe ([r/Fe]) in metal-poor stars preserves excellent information of the star formation history and provides important insights into the various situations of the Galactic chemical enrichment. In this respect, the upper and lower boundaries of [r/Fe] could present useful clues for investigating the extreme situations of the star formation history and the early Galactic chemical evolution. In this paper, we investigate the formation of the upper and lower boundaries of [r/Fe] for the gas clouds. We find that, for a cloud from which metal-poor stars formed, the formation of the upper limits of [r/Fe] is mainly due to the pollution from a single main r-process event. For a cloud from which metal-poor stars formed, the formation of the lower limits of [r/Fe] is mainly due to the pollution from a single SN II event that ejects primary Fe.