Apsidal motion and light-time effect in eclipsing binaries HS Herculis and U Ophiuchi

Several new times of minima, based on photoelectric observations, have been secured for two bright and well-known eclipsing binaries with eccentric orbits and with very similar orbital periods: HS Her (P = 1.(d)637, e = 0.02) and U Oph (P = 1.(d)677, e = 0.003). For HS Her, an apsidal motion with a period of 78 years is confirmed and a third body in an eccentric orbit with a period of 85 years is found. An analysis of all available eclipse timings of U Oph has confirmed the presence of an apsidal motion with one of the shortest known periods (20.1 yr) and a light-time effect with the improved period of 37.6 yr. The corresponding internal structure constants log k(2) were also derived. It is estimated that the tertiaries of both systems are detectable via speckle interferometry.