2. Observational data

The system was observed photoelectrically at the Ege University Observatory. The observations were performed in the observational season of 1994. The 48 cm (f/13) Cassegrain reflector equipped with an unrefrigerated EMI 9781 A photomultiplier tube was used. All observations were made with the B and V filters of the UBV system. A total of 197 observational points were obtained in each colour. BD 1278 and BD 1275 were used as comparison and check stars, respectively. Data related to the variable, comparison and check stars are given in \ Table 1 (click here). The atmospheric extinction coefficients in each colour for each night were calculated from the observations of the comparison star using conventional methods. Then, all the instrumental differential B and V magnitudes (in the sense variable minus comparison) were corrected for atmospheric extinction. Light and colour curves are shown in Fig. 1 (click here) and Fig. 2 (click here), respectively. The phases were calculated with the formula (2) which is given in Sect. 3.1.

The shape of the light curves of XY UMa in Fig. 1 (click here) are typical of Lyrae type. A pronounced asymmetry is evident in the light curves. This asymmetry is located between the descending and ascending shoulders of the primary minimum. In the literature, the existence of the asymmetry in the light curves of XY UMa has been stated and the responsibility was put on a star-spot activity. The fact that the asymmetry is observed in the phases of secondary minimum and afterwards, and also the unexpected light loss during these phases, might indicate to a star-spot activity on the surface of the primary component. The colour curve in Fig. gif (click here) shows that the system is redder at the primary and slightly bluer at the secondary minimum. So, the spectral type of the secondary component is later than that of the primary.