Nucleosynthesis in High-Entropy Hot-Bubbles of SNe and Abundance Patterns of Extremely Metal-Poor Stars

TL;DR

This study investigates whether normal supernovae with ejected hot-bubble matter can reproduce the abundance patterns of extremely metal-poor stars, finding that hypernovae are more naturally suited for this purpose.

Contribution

It demonstrates that ejection of specific hot-bubble matter from normal supernovae can match EMP star abundances, but hypernovae provide a more straightforward explanation.

Findings

Neutron-rich and proton-rich hot-bubble matter can increase Zn/Fe and Co/Fe ratios.

Fine-tuned ejection of slightly proton-rich matter from normal SNe can reproduce EMP abundances.

Hypernovae more easily reproduce EMP star abundance patterns without fine-tuning.

Abstract

There have been suggestions that the abundance of Extremely Metal-Poor (EMP) stars can be reproduced by Hypernovae (HNe), not by normal supernovae (SNe). However, recently it was also suggested that if the innermost neutron-rich or proton-rich matter is ejected, the abundance patterns of ejected matter are changed, and normal SNe may also reproduce the observations of EMP stars. In this letter, we calculate explosive nucleosynthesis with various Ye and entropy, and investigate whether normal SNe with this innermost matter, which we call "hot-bubble" component, can reproduce the abundance of EMP stars. We find that neutron-rich (Ye = 0.45-0.49) and proton-rich (Ye = 0.51-0.55) matter can increase Zn/Fe and Co/Fe ratios as observed, but tend to overproduce other Fe-peak elements. In addition to it, we find that if slightly proton-rich matter with 0.50 <= Ye < 0.501 with s/kb ~ 15-40 is ejected as much as ~ 0.06 Msolar, even normal SNe can reproduce the abundance of EMP stars, though it requires fine-tuning of Ye. On the other hand, HNe can more easily reproduce the observations of EMP stars without fine-tuning. Our results imply that HNe are the most possible origin of the abundance pattern of EMP stars.