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

Abstract

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 ($P = 1\fd637, e = 0.02$) and U Oph ($P = 1\fd677, e = 0.003$). 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.