2015MNRAS.453.2937Y

We present the Kepler photometric light-variation analysis of the late-type double-lined binary system V568 Lyr that is in the field of the high metallicity old open cluster NGC 6791. The radial velocity and the high-quality short-cadence light curve of the system are analysed simultaneously. The masses, radii and luminosities of the component stars are M1 = 1.0886±0.0031M_☉, M2 = 0.8292±0.0026M_☉, R1 = 1.4203±0.0058R_☉, R2 = 0.7997±0.0015R_☉, L1 = 1.85±0.15L_☉, L2 = 0.292±0.018L_☉ and their separation is a = 31.060±0.025R_☉. The distance to NGC 6791 is determined to be 4.260±0.290kpc by analysis of this binary system. We fit the components of this well-detached binary system with evolution models made with the Cambridge stars and ev(twin) codes to test low-mass binary star evolution. We find a good fit with a metallicity of Z = 0.04 and an age of 7.704Gyr. The standard tidal dissipation, included in ev(twin) is insufficient to arrive at the observed circular orbit unless it formed rather circular to begin with.