Magnetic modeling of inflated low-mass stars using interior fields no larger than ~10 kilogauss

TL;DR

This study presents magneto-convective models of low-mass stars with interior magnetic fields capped at 10 kG, successfully fitting observed stellar radii and temperatures, addressing previous criticisms of unrealistically large interior fields.

Contribution

The paper introduces low-mass star models with interior magnetic fields limited to 10 kG, aligning with dynamo theory and stability constraints, and fits empirical data effectively.

Findings

Models replicate observed stellar radii and temperatures for 14 stars.

Interior magnetic fields in models are constrained to no more than 10 kG.

One star's data fits well with a standard age, while another requires a younger age for compatibility.

Abstract

We have previously reported on models of low-mass stars in which the presence of inflated radii is ascribed to magnetic fields which impede the onset of convection (e.g. MacDonald & Mullan [2017a] and citations therein). Some of our magneto-convection models have been criticized because, when they were first reported by Mullan & MacDonald (2001), the deep interior fields were found to be very large (50-100 MG). Such large fields are now known to be untenable. For example, Browning et al. (2016) used stability arguments to suggest that interior fields in low-mass stars cannot be larger than ~1 MG. Moreover, 3D models of turbulent stellar dynamos suggest that fields generated in low-mass interiors may be not much stronger than 10-20 kG (Browning 2008). In the present paper, we present magneto-convective models of inflated low-mass stars in which the interior fields are not permitted to be stronger than 10 kG. These models are used to fit empirical data for 15 low-mass stars for which precise masses and radii have been measured. We show that our 10 kG magneto-convective models can replicate the empirical radii and effective temperatures for 14 of the stars. In the case of the remaining star (in the Praesepe cluster), two different solutions have been reported in the literature. We find that one of these solutions (by Gillen et al. 2017) can be fitted well with our model using the nominal age of Praesepe (800 Myr). However, the second solution (by Kraus et al. 2017) cannot be fitted unless the star's age is assumed to be much younger (~ 150 Myr).