Coronal Properties of Low-mass Population III Stars and the Radiative Feedback in the Early Universe

TL;DR

This study uses magnetohydrodynamic simulations to explore how magnetic fields influence the coronal properties of low-mass Population III stars and assesses their potential role in early universe reionization.

Contribution

It provides the first systematic analysis of coronal heating in metal-free stars and evaluates their radiative feedback on cosmic reionization.

Findings

Coronal temperature and density depend on magnetic field strength.

EUV and X-ray luminosities vary widely with magnetic field.

Low-mass Population III stars have a limited impact on reionization, but flares could contribute.

Abstract

We systematically investigated the heating of coronal loops on metal-free stars with various stellar masses and magnetic fields by magnetohydrodynamic simulations. It is found that the coronal property is dependent on the coronal magnetic field strength $B_{\rm c}$ because it affects the difference of the nonlinearity of the Alfv\'{e}nic waves. Weaker $B_{\rm c}$ leads to cooler and less dense coronae because most of the input waves dissipate in the lower atmosphere on account of the larger nonlinearity. Accordingly EUV and X-ray luminosities also correlate with $B_{\rm c}$, while they are emitted in a wide range of the field strength. Finally we extend our results to evaluating the contribution from low-mass Population III coronae to the cosmic reionization. Within the limited range of our parameters on magnetic fields and loop lengths, the EUV and X-ray radiations give a weak impact on the ionization and heating of the gas at high redshifts. However, there still remains a possibility of the contribution to the reionization from energetic flares involving long magnetic loops.