2019A&A...621A..93S

Aims. Our aim is to obtain high-accuracy measurements of the physical and orbital parameters of two evolved eclipsing binary systems, and to use these measurements to study their evolutionary status. We also aim to derive the distances to the systems by using a surface brightness-colour relation and compare these distances with the measurements provided by Gaia.
Methods. We measured the physical and orbital parameters of both systems based on V-band and I-band photometry from OGLE, near-infrared photometry obtained with the NTT telescope and the instrument SOFI, as well as high-resolution spectra obtained at ESO 3.6m/HARPS and Clay 6.5/MIKE spectrographs. The light curves and radial-velocity curves were analysed with the Wilson-Devinney code.
Results. We analysed two double-lined eclipsing binary systems OGLE-BLG-ECL-123903 and OGLE-BLG-ECL-296596 from the Optical Gravitational Lensing Experiment (OGLE) catalogue. Both systems have a configuration of two well-detached giants stars. The masses of the components of OGLE-BLG-ECL-123903 are M₁=2.045±0.027 and M₂=2.074±0.023M_☉ and the radii are R₁=9.540±0.049 and R₂=9.052±0.060R_☉. For OGLE-BLG-ECL-296596, the masses are M₁=1.093±0.015 and M₂=1.125±0.014M_☉, while the radii are R₁=18.06±0.28 and R₂=29.80±0.33R_☉. Evolutionary status was discussed based on the isochrones and evolutionary tracks fromPARSEC andMESA codes. The ages of the systems were established to be around 1.3Gyr for the OGLE-BLG-ECL-123903 and 7.7Gyr for the OGLE-BLG-ECL-296596. We also determined the distance to both systems. For OGLE-BLG-ECL-123903 this is equal to d=2.95±0.06(stat.)±0.07(syst.)kpc, while for the OGLE-BLG-ECL-296596 it is d=5.68±0.07(stat.)±0.14(syst.)kpc. This is the first analysis of its kind for these unique evolved eclipsing binary systems.