Apsidal motion and TESS light curves of three southern close eccentric eclipsing binaries: GM Nor, V397 Pup, and PT Vel^⋆

¹ Astronomical Institute, Faculty of Mathematics and Physics, Charles University Prague, V Holešovičkách 2, CZ-180 00 Praha 8, Czech Republic
² Institute of Theoretical Physics and Astrophysics, Masaryk University, Kotlářská 2, CZ-611 37 Brno, Czech Republic
³ FZU – Institute of Physics of the Czech Academy of Sciences, Na Slovance 1999/2, CZ-182 21 Praha 8, Czech Republic
⁴ Czech Astronomical Society, Variable Star and Exoplanet Section, Vídeňská 1056, CZ-142 00 Praha 4, Czech Republic
⁵ Observatory and planetarium Hradec Králové, Zámeček 456, CZ-500 08 Hradec Králové, Czech Republic
⁶ Private Observatory, CZ-683 41 Pavlovice 65, Czech Republic
⁷ Private Observatory, Plumstead, Cape Town, South Africa

Received: 9 April 2024
Accepted: 7 August 2024

Abstract

The study of apsidal motion in eccentric eclipsing binaries provides an important observational test of theoretical models of stellar structure and evolution. New ground-based and space-based photometric data have been obtained and archival spectroscopic measurements were used in this study of three detached early-type and southern-hemisphere eccentric eclipsing binaries GM Nor (P = 1^d​​.88, e = 0.05), V397 Pup (3^d​​.00, 0.30), and PT Vel (1^d​​.80, 0.12). Their TESS observations in several sectors have also been included and the corresponding light curves were solved using the PHOEBE code. As a result, new accurate photoelectric times of minimum light have been obtained. The newly completed O − C diagrams were analyzed using all reliable timings found in the literature and calculated using the TESS light curves. New or improved values for the elements of apsidal motion were obtained. Using ESO archive spectroscopy, for V397 Pup, the precise absolute parameters were newly derived: M₁ = 3.076(35) M_⊙, M₂ = 2.306(35) M_⊙, and R₁ = 2.711(55) R_⊙, R₂ = 1.680(55) R_⊙. For PT Vel the absolute dimensions were improved: M₁ = 2.204(25) M_⊙, M₂ = 1.638(25) M_⊙, and R₁ = 2.108(30) R_⊙, R₂ = 1.605(30) R_⊙. For GM Nor, the less accurate absolute parameters based on the light curve analysis were evaluated: M₁ = 1.94(15) M_⊙, M₂ = 1.84(14) M_⊙, and R₁ = 2.27(20) R_⊙, R₂ = 2.25(20) R_⊙. We found more precise and relatively short periods of apsidal motion of about 80, 335, and 160 years, along with the corresponding internal structure constants, log k₂, –2.524, –2.361, and –2.563, for GM Nor, V397 Pup, and PT Vel, respectively. Relativistic effects are small but not negligible, making up to 10% of the total apsidal motion rate in all systems. No marks of the presence of the third body were revealed in the light curves, on the O − C diagrams, or in the reduced spectra of the eccentric systems studied here.