Irradiated stars with convective envelopes

Astrophysics Group, Blackett Laboratory, Imperial College London, Prince Consort Road, London, SW7 2AZ, UK
e-mail: l.lucy@imperial.ac.uk

Received: 4 November 2016
Accepted: 26 March 2017

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%.