Alpha-constrained QSE Nucleosynthesis in High-entropy and Fast-expanding Material

TL;DR

This paper explores a unique nucleosynthesis process in high-entropy, rapidly expanding material, where heavy nuclei form a quasi-statistical equilibrium constrained by alpha particles, relevant to hypernova neutrino-driven winds.

Contribution

It introduces the concept of alpha-constrained QSE and demonstrates its role in synthesizing heavy nuclei in extreme astrophysical environments.

Findings

Heavy nuclei of A>100 achieve QSE at high temperature.

The process occurs in neutrino-driven winds from proto-neutron stars.

A~140 p-nuclei are synthesized in hypernova conditions.

Abstract

We investigate the nucleosynthesis process in high-entropy ($s/k_{\rm B}\gtrsim100$) and very fast-expanding ($\tau_{\rm exp}\sim10^{-3}\ {\rm s}$) materials. In such a material with the electron fraction near 0.5, an interesting nucleosynthesis process occurs. In this process, the abundance distribution of heavy-nuclei of $A>100$ achieve quasi-statistical equilibrium (QSE) at high temperature and the abundances are frozen at the end of the nucleosynthesis. We explain this abundance distribution using the "alpha-constrained QSE" abundances formulated in this paper. We demonstrate that this nucleosynthesis would occur in neutrino-driven winds from massive proto-neutron stars in hypernovae, where $A\sim140$ $p$-nuclei are synthesized.