Searching for detached EBs in large samples: the persistence of the radius anomaly in low-mass stars

The majority of the short-period low-mass eclipsing binaries in the literature, with orbital periods of less than 2 days, presents measured stellar radii that are usually 5 to 20% larger than the expected values when compared to stellar models. This inflation trend is known as the radius anomaly of low-mass stars. We have searched for low-mass eclipsing binaries within the Catalina Sky Survey and the Kepler databases to determine their orbital and physical parameters. We adopted a purely photometric method to derive stellar parameters, such as the effective temperature, photometric mass, and fractional radius, by using the available light curves and the broad-band photometry from 2MASS, SDSS and Pan-STARRS. We performed the light-curve fitting with the JKTEBOP code (suitable for detached systems), associated with an asexual genetic algorithm, to derive the best orbital solution the radius of each component. The adopted method allowed an unprecedented analysis of a large sample with a homogeneous set of parameters for low-mass stars in short-period binary systems, despite large individual uncertainties. We characterized a sample of 230 detached EBs from the CSS and 35 detached systems from Kepler EB catalog. The distribution of the studied components in the mass-radius diagram not only confirms the radius inflation in low-mass main-sequence stars but also shows a relative increase of inflation towards lower masses. The distribution also suggests that the secondary components of these short-period systems are more inflated than the primary components, as they present larger radii than primaries of the same mass when compared to stellar evolutionary models.