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, M-1 = 3.83 +/- 0.35 M-circle dot and M-2 = 3.27 +/- 0.35 M-circle dot; for V2544 Cyg, M-1 = 1.75 +/- 0.38 M-circle dot and M-2 = 1.40 +/- 0.38 M-circle dot; for V785 Cas, M-1 = 5.64 +/- 0.41 M-circle dot and M-2 = 5.18 +/- 0.41 M-circle dot. 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).