Analysis of Apsidal Motion and Light Curves of Three Eccentric Eclipsing Binaries: V398 Lac, V2544 Cyg and V785 Cas

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 (k2,obs and k2,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).