The TESS light curve of the eccentric eclipsing binary 1SWASP J011351.29+314909.7 – no evidence for a very hot M-dwarf companion

Abstract

A 2014 study of the eclipsing binary star 1SWASPJ011351.29+314909.7 (J0113+31) reported an unexpectedly high effective temperature for the M-dwarf companion to the 0.95-M? primary star. The effective temperature inferred from the secondary eclipse depth was ~600 K higher than the value predicted from stellar models. Such an anomalous result questions our understanding of low-mass stars and might indicate a significant uncertainty when inferring properties of exoplanets orbiting them. We seek to measure the effective temperature of the M-dwarf companion using the light curve of J0113+31 recently observed by the Transiting Exoplanet Survey Satellite (TESS). We use the pycheops modelling software to fit a combined transit and eclipse model to the TESS light curve. To calculate the secondary effective temperature, we compare the best-fitting eclipse depth to the predicted eclipse depths from theoretical stellar models. We determined the effective temperature of the M dwarf to be Teff,2 = 3208 ± 43 K, assuming log g2 = 5, [Fe/H] = -0.4, and no alpha-element enhancement. Varying these assumptions changes Teff,2 by less than 100 K. These results do not support a large anomaly between observed and theoretical low-mass star temperatures.