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

¹ Astronomical Institute, Charles University Prague, 180 00 Praha 8, V Holešovičkách 2, Czech Republic
² Astronomical Institute, Academy of Sciences, 251 65 Ondřejov, Czech Republic e-mail: hec@sunstel.asu.cas.cz
³ Astronomical Institute, University of Basel, Venusstrasse 7, 4102 Binningen, Switzerland e-mail: diethelm@astro.unibas.ch
⁴ Departamento de Astronomia, Universidad de Guanajuato, Apartado 144, 36000 Guanajuato, Gto, Mexico e-mail: eenens@astro.ugto.mx

Corresponding author: M. Wolf, wolf@mbox.cesnet.cz

Received: 22 October 2001
Accepted: 30 November 2001

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 () and U Oph (). 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 k₂ were also derived. It is estimated that the tertiaries of both systems are detectable via speckle interferometry.