The origins of light and heavy r-process elements identified by chemical tagging of metal-poor stars

TL;DR

This paper investigates the origins of light and heavy r-process elements in metal-poor stars, providing evidence that core-collapse supernovae produce light r-process elements while neutron star mergers produce heavy ones, with some mergers producing both.

Contribution

It offers new insights into the diverse nucleosynthesis processes in neutron star mergers and clarifies the roles of supernovae and mergers in r-process element production.

Findings

Core-collapse supernovae produce light r-process elements.

Neutron star mergers are responsible for heavy r-process elements.

Some neutron star mergers produce both light and heavy r-process elements.

Abstract

Growing interests in neutron star (NS) mergers as the origin of r-process elements have sprouted since the discovery of evidence for the ejection of these elements from a short-duration gamma-ray burst. The hypothesis of a NS merger origin is reinforced by a theoretical update of nucleosynthesis in NS mergers successful in yielding r-process nuclides with A>130. On the other hand, whether the origin of light r-process elements are associated with nucleosynthesis in NS merger events remains unclear. We find a signature of nucleosynthesis in NS mergers from peculiar chemical abundances of stars belonging to the Galactic globular cluster M15. This finding combined with the recent nucleosynthesis results implies a potential diversity of nucleosynthesis in NS mergers. Based on these considerations, we are successful in the interpretation of an observed correlation between [light r-process/Eu] and [Eu/Fe] among Galactic halo stars and accordingly narrow down the role of supernova nucleosynthesis in the r-process production site. We conclude that the tight correlation by a large fraction of halo stars is attributable to the fact that core-collapse supernovae produce light r-process elements while heavy r-process elements such as Eu and Ba are produced by NS mergers. On the other hand, stars in the outlier, composed of r-enhanced stars ([Eu/Fe]>+1) such as CS22892-052, were exclusively enriched by matter ejected by a subclass of NS mergers that is inclined to be massive and consist of both light and heavy r-process nuclides.