Coronal properties of low-mass Population III stars and the radiative feedback in the early universe

Abstract

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 Bc because it affects the difference of the non-linearity of the Alfvénic waves. Weaker Bc leads to cooler and less dense coronae because most of the input waves dissipate in the lower atmosphere on account of the larger non-linearity. Accordingly EUV and X-ray luminosities also correlate with Bc, 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.