Apsidal motion in five eccentric eclipsing binaries

Abstract

Aims. As part of the long-term Ondand Ostrava observational projects, we aim to measure the precise times of minimum light for eccentric eclipsing binaries, needed for accurate determination of apsidal motion. Over fifty new times of minimum light recorded with CCD photometers were obtained for five early-type and eccentric-orbit eclipsing binaries: V785 Cas (P = 2. 70, e = 0.09), V821 Cas (1. d 77, 0.14), V796 Cyg (1. d 48, 0.07), V398 Lac (5. d 41, 0.23), and V871 Per (3. d 02, 0.24). Methods. O−C diagrams of binaries were analysed using all reliable timings found in the literature, and new elements of apsidal motion were obtained. Results. We derived for the first time or improved the relatively short periods of apsidal motion of about 83, 140, 33, 440, and 70 years for V785 Cas, V821 Cas, V796 Cyg, V398 Lac, and V871 Per, respectively. The internal structure constants, log k2, for V821 Cas and V398 Lac are then found to be -2.70 and -2.35, under the assumption that the component stars rotate pseudosynchronously. The relativistic effects are weak, up to 7% of the total apsidal motion rate.