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Research in Astronomy and Astrophysics, vol.25, no.10, 2025 (SCI-Expanded)
In this study, the apsidal motion analyses of the eclipsing binary systems V398 Lac, V2544 Cyg, and V785 Cas are presented. The (O − C) diagrams of the selected systems were constructed using all available and reliable times of minimum light compiled from the literature. As a result, the apsidal motion periods were determined to be 353 ± 50 yr, 43.3 ± 5.1 yr and 83.4 ± 8.5 yr, respectively. Furthermore, the TESS light curves of the three systems were analyzed to derive their photometric and absolute parameters. The component masses were determined as follows: for V398 Lac, M1 = 3.83 ± 0.35 M⊙ and M2 = 3.27 ± 0.35 M⊙; for V2544 Cyg, M1 = 1.75 ± 0.38 M⊙ and M2 = 1.40 ± 0.38 M⊙; for V785 Cas, M1 = 5.64 ± 0.41 M⊙ and M2 = 5.18 ± 0.41 M⊙. The parameters related to apsidal motion, as well as the observational and theoretical internal structure constants ( k ¯ 2 , obs and k ¯ 2 , teo ), were calculated for studied binaries. The relativistic contribution to the observed apsidal motion rate was found to be relatively small, constituting less than approximately 5% of the total rate in each system. The theoretical internal structure constants were derived from the evolutionary models, assuming a standard chemical composition of (X, Z) = (0.70, 0.01).