Absolute dimensions and apsidal motion of the eclipsing binaries V889 Aquilae and V402 Lacertae

¹ Institut de Ciències de l’Espai (ICE, CSIC), Campus UAB, c/ Can Magrans s/n, 08193 Bellaterra, Barcelona, Spain
² Institut d’Estudis Espacials de Catalunya (IEEC), c/ Gran Capità 2-4, 08034 Barcelona, Spain
e-mail: baroch@ieec.cat
³ Centro de Astrobiología (CSIC-INTA), Ctra. Ajalvir, km 4., 28850 Torrejón de Ardoz, Madrid, Spain
⁴ Department of Physics, Ariel University, 40700 Ariel, Israel
⁵ Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
⁶ Dept. Física Quàntica i Astrofísica, Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (IEEC-UB), Martí i Franquès 1, 08028 Barcelona, Spain
⁷ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
⁸ Instituto de Astrofísica de Canarias, Vía Láctea S/N, 38205 La Laguna, Tenerife, Spain
⁹ Universidad de La Laguna, Departamento de Astrofísica, 38206 La Laguna, Tenerife, Spain

Received: 16 June 2022
Accepted: 24 June 2022

Abstract

Context. Double-lined eclipsing binaries allow the direct determination of masses and radii, which are key for testing stellar models. With the launch of the TESS mission, many well-known eclipsing binaries have been observed at higher photometric precision, permitting the improvement of the absolute dimension determinations.

Aims. Using TESS data and newly obtained spectroscopic observations, we aim to determine the masses and radii of the eccentric eclipsing binary systems V889 Aql and V402 Lac, together with their apsidal motion parameters.

Methods. We simultaneously modelled radial velocity curves and times of eclipse for each target to precisely determine the orbital parameters of the systems, which we used to analyse the light curves and then obtain their absolute dimensions. We compared the obtained values with those predicted by theoretical models.

Results. We determined masses and radii of the components of both systems with relative uncertainties lower than 2%. V889 Aql is composed of two stars with masses 2.17 ± 0.02 M_⊙ and 2.13 ± 0.01 M_⊙ and radii 1.87 ± 0.04 R_⊙ and 1.85 ± 0.04 R_⊙. We find conclusive evidence of the presence of a third body orbiting V889 Aql with a period of 67 yr. Based on the detected third light and the absence of signal in the spectra, we suggest that this third body could in turn be a binary composed of two ∼1.4 M_⊙ stars. V402 Lac is composed of two stars with masses 2.80 ± 0.05 M_⊙ and 2.78 ± 0.05 M_⊙ and radii 2.38 ± 0.03 R_⊙ and 2.36 ± 0.03 R_⊙. The times of minimum light are compatible with the presence of a third body for this system too, although its period is not yet fully sampled. In both cases we have found a good agreement between the observed apsidal motion rates and the model predictions.