Evolved eclipsing binary systems in the Galactic bulge: Precise physical and orbital parameters of OGLE-BLG-ECL-305487 and OGLE-BLG-ECL-116218

¹ Nicolaus Copernicus Astronomical Centre, Bartycka 18, 00-716 Warsaw, Poland
e-mail: ksenia@camk.edu.pl
² Nicolaus Copernicus Astronomical Centre, Rabiańska 8, 87-100 Toruń, Poland
³ Departamento de Astronomía, Universidad de Concepción, Casilla 160-C, Concepción, Chile
⁴ Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 911101-1292, USA

Received: 6 July 2022
Accepted: 30 September 2022

Abstract

Aims. Our goal is to determine, with high accuracy, the physical and orbital parameters of two double-lined eclipsing binary systems, where the components are two giant stars. We also aim to study the evolutionary status of the binaries, to derive the distances towards them by using a surface brightness–colour relation, and to compare these measurements with the measurements presented by the Gaia mission.

Methods. In order to measure the physical and orbital parameters of the systems, we analysed the light curves and radial-velocity curves with the Wilson–Devinney code. We used V-band and I-band photometry from the Optical Gravitational Lensing Experiment (OGLE) catalogue and near-infrared photometry obtained with the New Technology Telescope (NTT) equipped with the SOFI instrument. The spectroscopic data were collected with the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph mounted at the ESO 3.6-m telescope and the Magellan Inamori Kyocera Echelle (MIKE) spectrograph mounted at the 6.5-m Clay telescope.

Results. We present the first analysis of this kind for two evolved eclipsing binary systems from the OGLE catalogue: OGLE-BLG-ECL-305487 and OGLE-BLG-ECL-116218. The masses of the components of OGLE-BLG-ECL-305487 are M₁ = 1.059 ± 0.019 and M₂ = 0.991 ± 0.018 M_⊙, and the radii are R₁ = 19.27 ± 0.28 and R₂ = 29.99 ± 0.24 R_⊙. For OGLE-BLG-ECL-116218, the masses are M₁ = 0.969 ± 0.012 and M₂ = 0.983 ± 0.012 M_⊙, while the radii are R₁ = 16.73 ± 0.28 and R₂ = 22.06 ± 0.26 R_⊙. The evolutionary status of the systems is discussed based on the PARSEC and MIST isochrones. The ages of the systems were established to be between 7.3–10.9 Gyr for OGLE-BLG-ECL-305487 and around 10 Gyr for OGLE-BLG-ECL-116218. We also measured the distances to the binaries. For OGLE-BLG-ECL-305487, d = 7.80 ± 0.18 (stat.) ± 0.19 (syst.) kpc and for OGLE-BLG-ECL-116218, d = 7.57 ± 0.28 (stat.) ± 0.19 (syst.) kpc.