Empirical measures of the largest amounts of magnetically-induced radius inflation in low-mass stars

TL;DR

This study uses empirical data from eclipsing binaries to estimate the maximum magnetic field strengths inside low-mass stars, linking magnetic activity to observed stellar radius inflation.

Contribution

It introduces a method to set upper limits on internal magnetic field strengths in low-mass stars based on empirical radius inflation measurements.

Findings

Magnetic field strengths of about 10 kG can explain radius inflation in stars >0.65 MSun.

Lower mass stars (<0.4 MSun) may require magnetic fields of 100-300 kG to account for inflation.

The approach constrains internal magnetic fields using observational data and magneto-convective modeling.

Abstract

Access to precise empirical estimates of stellar radii in recent decades has revealed that the radii of certain low-mass stars are inflated relative to stellar structure predictions. The largest inflations are found in magnetically active stars. Although various attempts have been made to incorporate magnetic effects into stellar structure codes, a major source of uncertainty is associated with our lack of knowledge as to how the field strength varies inside the star. Here, we point out that a recent study of 44 eclipsing binaries in the Kepler field by Cruz et al. may enable us for the first time to set an upper limit Bc on the field strengths inside the 88 stars in the sample. According to our magneto-convective model, the largest empirical inflations reported by Cruz et al. can be replicated if Bc is about 10 kG inside stars with masses greater than 0.65 MSun. On the other hand, in lower mass stars, especially those with masses less than 0.4 MSun, our model predicts that the largest empirical inflations may require significantly stronger fields, i.e. Bc approximately 100-300 kG.