Magnetic Inhibition of Convection and the Fundamental Properties of Low-Mass Stars. II. Fully Convective Main Sequence Stars

TL;DR

This study investigates whether magnetic fields can explain the inflated radii of fully convective main sequence stars in binary systems, finding current models insufficient unless extremely strong magnetic fields are present.

Contribution

It critically assesses magnetic field hypotheses for stellar inflation and evaluates the physical plausibility of generating such strong interior magnetic fields.

Findings

Magnetic models cannot reproduce observed stellar radii without >10 MG interior fields.

Current models lack evidence that such strong magnetic fields are physically feasible.

Star spots are unlikely to be the primary cause of stellar inflation in these stars.

Abstract

We examine the hypothesis that magnetic fields are inflating the radii of fully convective main sequence stars in detached eclipsing binaries (DEBs). The magnetic Dartmouth stellar evolution code is used to analyze two systems in particular: Kepler-16 and CM Draconis. Magneto-convection is treated assuming stabilization of convection and also by assuming reductions in convective efficiency due to a turbulent dynamo. We find that magnetic stellar models are unable to reproduce the properties of inflated fully convective main sequence stars, unless strong interior magnetic fields in excess of 10 MG are present. Validation of the magnetic field hypothesis given the current generation of magnetic stellar evolution models therefore depends critically on whether the generation and maintenance of strong interior magnetic fields is physically possible. An examination of this requirement is provided. Additionally, an analysis of previous studies invoking the influence of star spots is presented to assess the suggestion that star spots are inflating stars and biasing light curve analyses toward larger radii. From our analysis, we find that there is not yet sufficient evidence to definitively support the hypothesis that magnetic fields are responsible for the observed inflation among fully convective main sequence stars in DEBs.