THE ORBITAL PERIOD STUDY AND PHOTOMETRIC ANALYSIS OF XY URSAE-MAJORIS

Photoelectric observations of the eclipsing binary XY UMa have been ca rried out in B and V colours at the Ege University Observatory. Combin ing these newly obtained data with the previous ones available in the literature, the problem pertaining to the orbital period of the system has been investigated through a detailed description of the O-C diagr am. The sinusoidal and secular changes have been found. Such variation s of the orbital period have been examined in terms of three plausible mechanisms, namely (i) a light-time effect due to a third body, (ii) the orbital period modulation due to magnetic activity cycle of a comp onent star, and (iii) a mass loss case in which the ejected material e scapes out from the binary system. A combination of a magnetic activit y cy de mechanism and a mass loss case is found to reproduce satisfact orily the period changes. Further, the observed photoelectric light cu rves of the system have been analyzed with the Wilson-Devinney approac h. This analysis shows that the asymmetries of the light curves of XY UMa can be interpreted in terms of cool star-spot covering 7% of the s tellar photosphere of the primary component of this binary. The system is found to be a beta Lyrae type detached binary. The absolute elemen ts of the system are also deduced.