Apsidal motion and TESS light curves of two southern eclipsing binaries with high eccentricity: V1647 Sgr and V2283 Sgr

¹ Astronomical Institute, Faculty of Mathematics and Physics, Charles University Prague V Holešovičkách 2 CZ-180 00 Praha 8, Czech Republic
² Department 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

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 5 September 2025
Accepted: 30 January 2026

Abstract

The study of apsidal motion rates in eccentric eclipsing binaries provides an important observational test of theoretical models of stellar structure and evolution. Precise physical parameters of the stellar components together with systematic measurements of the periastron advance are needed. We present new results of our long-term observational project to analyze the apsidal motion in early-type eccentric eclipsing binaries. New ground- and space-based photometric data were obtained, and archival spectroscopic measurements were used in this study of two detached southern hemisphere eclipsing binaries: V1647 Sgr (P = 3_.^d,e = 0.41), and V2283 Sgr (3_.^d,47, 0.49). Their TESS observations in four sectors were also included, and the corresponding light curves were solved using the code PHOEBE. 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 were obtained for the elements of apsidal motion. Using archival spectroscopy for V1647 Sgr, we improved the precise absolute parameters to M₁ = 2.184(0.035) M_⊙, M₂ = 1.957(0.035) M_⊙, and R₁ = 1.839(0.015) R_⊙, R₂ = 1.716(0.015) R_⊙. For V2283 Sgr, the absolute dimensions were newly estimated to M₁ = 2.178(0.10) M_⊙, M₂ = 1.547(0.10) M_⊙, and R₁ = 1.796(0.01) R_⊙, R₂ = 1.544(0.01) R_⊙. We improved relatively long periods of apsidal motion of about 580 and 530 years, together with the corresponding internal structure constants, log k₂, –2.394, and –2.418, for V1647 Sgr and V2283 Sgr, respectively. The relativistic contribution to apsidal motion is not negligible. It is about 12 and 14% of the total rate of apsidal motion for V1647 Sgr and V2283 Sgr, respectively. No signs of an additional body were revealed in the light curves or in the O − C diagrams of the two eccentric systems.