Abstrakt
We present new results of our long-term observational project to analyze the variations of the orbital period for early-type eccentric eclipsing binaries. Altogether 77 new mid-eclipse times were measured or derived for two eclipsing binaries, namely V539 Ara and V335 Ser.
Based on current O - C diagrams, we found in both systems that times of minima besides the typical apsidal motion show additional cyclical changes likely caused by the third or fourth bodies orbiting the eclipsing pair. The improved periods of apsidal motion are 155 and 1080 years, respectively.
For the first time we propose a third and fourth body orbiting V539 Ara, stellar companions in a hierarchical system with a minimal mass of 0.41 and 1.74 M-circle dot. In V355 Ser we found a possible third body with a mass of 0.18 M-circle dot orbiting this eclipsing pair.
The third- and fourth-body orbital periods are relatively short 29 and 57 yr in case of V539 Ara, and 25 yr for V335 Ser.