Photometric Study on the Spot-Double Star XY Urase Majoris (I)

The long-term observational properties of the photometric behaviours of the short period (p=0.48 day) eclipsing binary system XY UMa are discussed. They are based on the UBV observations, which were carried out by Geyer in the years 1955-1961, 1968, 1975-1984. Light curves of XY UMa revealed very large changes not only between consecutive observing nights, but also from season to season. Between 1955 and 1984, the mean system brightness increased about 30% during this time intervals, meanwhile, the orbital period of this system was constant whithin 1.6% of its period. The colour index curve shows similar variations like the light curve but with a phase offset oscillation around the time instants of the primary minima. Observational evidence for photospheric and chromospheric activities on the XY UMa are also discussed