Explosive Nucleosynthesis of Weak r-Process Elements in Extremely Metal-Poor Core-Collapse Supernovae

TL;DR

This study explores how explosive nucleosynthesis in high-energy supernovae can produce weak r-process elements like Sr, Y, and Zr, explaining their high abundance in extremely metal-poor stars, unlike normal supernovae.

Contribution

It demonstrates that hypernovae can reproduce observed weak r-process element abundances, highlighting the importance of high entropy flows in nucleosynthesis models.

Findings

Hypernovae can produce high Sr, Y, Zr abundances.

Normal supernovae cannot reproduce these element ratios.

High entropy flows are necessary for element ejection in normal supernovae.

Abstract

There have been attempts to fit the abundance patterns of extremely metal-poor stars with supernova nucleosynthesis models for the lighter elements than Zn. On the other hand, observations have revealed that the presence of EMP stars with peculiarly high ratio of "weak r-process elements" Sr, Y and Zr. Although several possible processes were suggested for the origin of these elements, the complete solution for reproducing those ratios is not found yet. In order to reproduce the abundance patterns of such stars, we investigate a model with neutron rich matter ejection from the inner region of the conventional mass-cut. We find that explosive nucleosynthesis in a high energy supernova (or "hypernova") can reproduce the high abundances of Sr, Y and Zr but that the enhancements of Sr, Y and Zr are not achieved by nucleosynthesis in a normal supernova. Our results imply that, if these elements are ejected from a normal supernova, nucleosynthesis in higher entropy flow than that of the supernova shock is required.