A&A Supplement series, Vol. 127, January II 1998, 257-267
Received December 9, 1996; accepted May 9, 1997
A. Erdem and N. Güdür
Send offprint request: A. Erdem
Department of Physics, Faculty of Arts and Sciences, Canakkale Onsekiz, Mart
University, 17100 Canakkale, Turkey
e-mail: comummfd@turnet.net.tr
or aerdem@bornova.ege.edu.tr
Photoelectric observations of the eclipsing binary XY UMa
have been carried out in B and V colours at the Ege University
Observatory. Combining 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
diagram. The sinusoidal and secular changes have been found.
Such variations 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 component star,
and (iii) a mass loss
case in which the ejected material escapes out
from the binary system. A combination of a magnetic activity
cycle mechanism and a mass loss case is
found to reproduce satisfactorily the period changes.
Further, the observed photoelectric light curves of the system
have been analyzed with the Wilson-Devinney approach.
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 stellar photosphere of the primary component
of this binary. The system is found to be a
Lyrae type detached binary. The
absolute elements of the system are also deduced.
keywords: stars: binaries -- close -- stars: individual -- XY UMa -- fundamental parameters -- starspots