Evolution of Low-Mass Population III Stars: Convection, Mass Loss, Nucleosynthesis, and Neutrinos

TL;DR

This paper models the evolution of low-mass Population III stars using hydrodynamic simulations to explore how uncertain physics affects their nucleosynthesis, remnants, and potential observational signatures, aiding in identifying surviving ancient stars.

Contribution

It introduces detailed evolutionary models for low-mass Pop III stars, systematically analyzing the impact of physics uncertainties on their evolution and observable features.

Findings

Surface enrichment from convective shell mergers

Predicted properties of Pop III white dwarf remnants

Potential neutrino signals during shell events

Abstract

The first stars likely formed from pristine clouds, marking a transformative epoch after the dark ages by initiating reionisation and synthesising the first heavy elements. Among these, low-mass Population III stars are of particular interest, as their long lifespans raise the possibility that some may survive to the present day in the Milky Way's stellar halo or satellite dwarfs. As the first paper in a series, we present hydrodynamic evolutionary models for 0.7 - 1 MSun stars evolved up to the white dwarf phase, utilising the MESA software instrument. We systematically vary mass-loss efficiencies, convective transport, and overshooting prescriptions, thereby mapping how uncertain physics influences nucleosynthetic yields; surface enrichment, including nitrogen-rich post-main sequence stars arising from convective shell mergers; remnant properties, such as low-mass helium or carbon-oxygen white dwarfs (M_WD ~ 0.45-0.55 MSun) and transient UV-bright phases; and potential observational signatures, including neutrino emission during shell mergers and helium flashes. These models establish a predictive framework for identifying surviving Pop III stars and their descendants, providing both evolutionary and observational constraints that were previously unexplored.