The radius inflation problem in short-period low-mass binaries: a large sample analysis

Abstract

Due to the recent increase in the availability of photometric time-series databases, the characterisation of low-mass eclipsing binaries for the study of their orbital and physical parameters is now possible in large samples and with good precision. We have identified and photometrically characterised a sample of 230 detached close-orbiting eclipsing binaries with low-mass main-sequence components in the Catalina Sky Survey. These low-mass stars have masses of $M \leq 1.0\ M_{\odot}$ and orbital periods shorter than $2$ days. The adopted method provided a robust estimate of stellar parameters (as mass and fractional radius) by using only light curves and photometric colours, since no spectroscopic information was available for these objects. A SDSS-2MASS ten-colour grid of composite synthetic and observed colours and the K-Nearest Neighbours method were employed to identify main-sequence stars and to estimate their effective temperatures, typically of $T_{\rm eff}\leq 5720$ K. Each light curve was modelled with the JKTEBOP code together with an asexual genetic algorithm to obtain the most coherent values for the fitted parameters. The present work provides an unprecedented number of homogeneous estimates of main stellar parameters in short-period low-mass binary systems. The distribution of the components of the investigated detached eclipsing binaries in the mass-radius diagram supports a trend of radius inflation on low-mass main-sequence stars. A relative increase of inflation for lower masses is also found and our results suggest that the secondaries are more inflated, i.e. they present larger radii than the primary components of same mass, when compared to stellar evolutionary models.