2011A&A...526A..29H

We present the results of our detailed spectroscopic and photometric analysis of two previously unknown <1M_☉ detached eclipsing binaries: ASAS J045304-0700.4 and ASAS J082552-1622.8. With the HIgh Resolution Echelle Spectrometer (HIRES) on the Keck-I telescope, we obtained spectra of both objects covering large fractions of orbits of the systems. We also obtained V and I band photometry with the 1.0-m Elizabeth telescope of the South African Astronomical Observatory (SAAO). The orbital and physical parameters of the systems were derived with the PHOEBE and JKTEBOP codes. We investigated the evolutionary status of both binaries with several sets of widely-used isochrones. Our modelling indicates that (1) ASAS J045304-0700.4 is an old, metal-poor, active system with component masses of M₁=0.8338±0.0036M_☉, M₂=0.8280±0.0040M_☉ and radii of R₁=0.848±0.005R_☉ and R₂=0.833±0.005R_☉, which places it at the end of the Main Sequence evolution - a stage rarely observed for this type of stars. (2) ASAS J082552-1622.8 is a metal-rich, active binary with component masses of M₁=0.7029±0.0045M_☉, M₂=0.6872±0.0049M_☉ and radii of R₁=0.694 ^+0.007_–0.011R_☉ and R₂=0.699 ^+0.011_–0.014R_☉. Both systems show significant out-of-eclipse variations, probably owing to large, cold spots. We also investigated the influence of a third light in the second system.