MASS TRANSFER AND LIGHT TIME EFFECT STUDIES FOR AU SERPENTIS

The orbital period changes of theWUMa eclipsing binary AU Ser are studied using the (O?C) method. We conclude that the period variation is due to mass transfer from the primary star to the secondary one at a very low and decreasing rate dP/dt = ?8.872× 10 ?8 , superimposed on the sinusoidal variation due to a third body orbiting the binary with period 42.87 ± 3.16 years, orbital eccentricity e = 0.52±0.12 and a longitude of periastron passage ! = 133°.7±15. On studying the magnetic activity, we have concluded that the Applegate mechanism failed to describe the cycling variation of the (O ? C) diagram of AU Ser.