A PERIOD STUDY OF V502-OPHIUCHUS

All available published times of minima of a W-type contact binary V502 Oph have been compiled and critically examined. We revised ten times of minima from original observations, and derived five new times of minima from our own observations. A period study covering 53 yr of observations including 84 timings of minima light (63 of them from photoelectric observations) reveals that the orbital period of the system oscillates with a period of about 35 +/- 2 yr and amplitude of about 0.020 +/- 0.005 day while it undergoes a constant period decrease of about dP/dt almost-equal-to -1.45 10(-7) d yr-1. To satisfy such period decrease, a conservative mass transfer rate (with no magnetic effect) from more massive to less massive component would be of the order of 10(-7) M. yr-1. However, continuous angular momentum loss due to magnetically driven wind is inevitable since the system is formed of two late type (G2V + F9V) convective components. We found no grounds to support any relation between the period oscillation and the asymmetry measures of the light curves of V502 Oph. We think the most likely explanation of the period oscillation is the light time effect. A preliminary solution reveals that the hypothetical third body is at least 4 mag fainter than V502 Oph and has a very small mass of about 0.3 M..