The r-process in proto-neutron-star wind revisited

TL;DR

This study revisits the r-process nucleosynthesis in proto-neutron-star winds, exploring how different neutron star masses influence element production, and suggests PNS winds mainly produce light trans-iron elements and some low-level heavy elements.

Contribution

It provides a detailed analysis of r-process nucleosynthesis in PNS winds across a range of neutron star masses, incorporating recent findings on neutron-richness and massive neutron stars.

Findings

PNS winds produce Sr, Y, Zr via a weak r-process.

Massive PNS (>2.0 M_sun) can eject some heavy r-process elements.

PNS winds account for up to 10% of elements heavier than A~110.

Abstract

We examine the r-process in the neutrino-driven proto-neutron-star (PNS) wind of core-collapse supernovae in light of the recent findings of massive neutron stars in binaries as well as of an indication of neutron-richness in the PNS ejecta because of the nucleon potential corrections on neutrino opacities. To this end, a spherically symmetric, general relativistic, steady-state wind model is applied for a wide range of PNS masses between 1.2 M_sun and 2.4 M_sun with the latter reaching the causality limit. Nucleosynthesis calculations with these PNS models are performed by assuming a time evolution of electron fraction with its minimal value of Y_e = 0.4, which mimics recent hydrodynamical results. The fundamental nucleosynthetic aspect of the PNS wind is found to be the production of Sr, Y and Zr in quasi-equilibrium and of the elements with A = 90-110 by a weak r-process, which can be an explanation for the abundance signatures in r-process-poor Galactic halo stars. PNSs more massive than 2.0 M_sun can eject heavy r-process elements, however, with substantially smaller amount than what is needed to account for the solar content. PNS winds can be thus the major origin of light trans-iron elements but no more than 10% of those heavier than A ~ 110, although they may be the sources of the low-level abundances of Sr and Ba found in numerous metal-poor stars if the maximum mass of PNS exceeds 2.0 M_sun.