AN ORBITAL PERIOD STUDY OF THE CONTACT SYSTEM AB ANDROMEDAE

The O-C curve of the contact binary AB Andromedae is analyzed using a new method which enables the calculation of the orbital period P(E) an d its rate of change dP/P as continuous functions of time. A critical consideration of the most probable physical mechanisms that modulate t he orbital period in the observed way, is made on the basis of a perio dic (i.e. Applegate mechanism, third body assumption) or non-periodic (i.e. main circulation system, stability properties) modulation. Short -time period variations can be explained by more than one way, while d ifficulties remain in the identification of the possible origin of the detected long-time period variation. Furthermore, the possible modula tion of a W-class W UMa-type light curve by the Applegate mechanism is also examined.