Irradiated stars with convective envelopes

TL;DR

This paper investigates whether irradiation from close companions can explain the observed radius inflation in M dwarfs, concluding that irradiation effects are too small to account for the ~5% discrepancy.

Contribution

The study models the impact of irradiation on low-mass stars' structure, quantifying its effect on stellar radii and luminosities, and finds it insufficient to explain the observed radius anomaly.

Findings

Irradiation causes less than 0.4% radius inflation in similar-mass M dwarf binaries.

Stronger irradiation leads to a maximum of about 5% radius inflation due to saturation effects.

Irradiation effects are too small to explain the observed 5% radius discrepancy in M dwarfs.

Abstract

The observed radii of M dwarfs in eclipsing binaries exceed predicted radii by ~ 5%. To investigate this anomaly, the structure of low-mass stars irradiated by a close companion is considered. Irradiation modifies the surface boundary conditions and thereby also the adiabatic constants of their outer convection zones. This changes the models' radii and luminosities. For short-period M dwarf binaries with components of similar mass, radius inflation due to their mutual irradiation is found to be < 0.4%. This is an order of magnitude too small to explain the observed anomaly. Although stronger irradiation results in a monotonically increasing radius, a saturation effect limits the inflation to <~ 5\%.