Twin stars as tracers of binary evolution in the Kepler era

We present results of the combined photometric and spectroscopic analysis of four systems that are eclipsing binaries with a twin component (mass ratio q similar or equal to 1). These are exceptional tools to provide information for probing the internal structure of stars. None of the systems were previously recognized as twin binaries. We used a number of high-resolution optical spectra to calculate the radial velocities and later combined them with photometry to derive orbital parameters. Temperatures and metallicities of systems were estimated from high-resolution spectra. For each binary, we obtained a full set of orbital and physical parameters, reaching precision below 3 per cent in masses and radii for whole pairs. By comparing our results with PARSEC and MIST isochrones, we assess the distance, age, and evolutionary status of the researched objects. The primary and/or secondary stars of EPIC216075815 and EPIC202843107 are one of the cases where asteroseismic parameters of delta Sct and gamma Dor pulsators were confirmed by an independent method and rare examples of the twin-eclipsing binaries therefore the following analyses and results concern the pulsating nature of the components.