The Effect of Mass Loss and Convective Overshooting on the Pre-Collapse Structure, Composition, and Neutrino Emission of Red Supergiants

TL;DR

This study investigates how mass loss and convective overshooting in stellar models influence the pre-collapse core properties and neutrino emissions of red supergiants, revealing complex core dynamics before supernovae.

Contribution

First comprehensive analysis of combined effects of mass loss and convective overshooting on RSG pre-supernova core structure and neutrino signals using detailed stellar modeling.

Findings

Core contraction, heating, and deleptonization occur in the last days of RSGs.

Core silicon and shell burning episodes cause temporary core expansion and mixing.

Pre-supernova neutrino spectra shift to higher energies and fluxes, dominated by beta processes hours before collapse.

Abstract

Prior to core collapse, the neutrino emission from red supergiants (RSGs) is so large that a nearby ($\lesssim1$kpc) RSG will become visible in current and near-future neutrino detectors. The rate of emission and the spectra of the pre-supernova (pre-SN) neutrinos from RSGs are sensitive to the temperature, density, and detailed isotopic composition of the core. During the last year of the star's life, these properties change considerably. Several factors of stellar evolution modeling - such as the treatment of mass loss and convective overshooting - alter the thermal conditions and composition of the RSG core as it approaches collapse. In this paper we present the first study of how varying the treatment of mass loss and convective overshooting together affects the pre-collapse core properties and neutrino emission of RSGs. We use the stellar evolution instrument MESA and construct a grid of 32 models with zero-age main sequence masses of $\{ 12, 15, 18, 20\}$ $M_\odot$, use the so-called 'Dutch' mass-loss scheme with wind efficiencies of $\{0.2, 0.4, 0.8, 1.0\}$, and consider two convective overshooting schemes. Our models use a large 206-isotope nuclear network in order to accurately compute the structure and composition of the star. We find that, in the last few days of the star's life, the general trend of the conditions and composition in the core of the star is one of contraction, heating, and deleptonization, but that during this phase, this general trend will be interrupted by the initiation of core silicon burning and shell burning episodes that cause the core to expand and undergo convective mixing with material of a higher proton fraction that temporarily reverses the deleptonization. The pre-SN neutrino emission reflects these changes with a gradual shift to higher energies and larger flux that becomes dominated by beta processes a few hours prior to the collapse.