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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 tex2html_wrap_inline1881 1278 and BD tex2html_wrap_inline1881 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 tex2html_wrap_inline1815 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.

Figure 1: Differential B and V light curves of XY UMa for 1994

Figure 2: tex2html_wrap_inline1865 colour curve of XY UMa for 1994


Star BD No HD No tex2html_wrap_inline1867 (1900) tex2html_wrap_inline1869 (1900) tex2html_wrap_inline1871 tex2html_wrap_inline1873 Sp.
XY UMa +55tex2html_wrap_inline1829 1317 27143 tex2html_wrap_inline1877 tex2html_wrap_inline1879 tex2html_wrap_inline1881 tex2html_wrap_inline1883 tex2html_wrap_inline1885 tex2html_wrap_inline1887 G2-G5
Comparison tex2html_wrap_inline1881 1278 237784 tex2html_wrap_inline1877 tex2html_wrap_inline1893 tex2html_wrap_inline1881 tex2html_wrap_inline1897 tex2html_wrap_inline1899 tex2html_wrap_inline1901 F5
Check tex2html_wrap_inline1881 1275 233599 tex2html_wrap_inline1877 tex2html_wrap_inline1907 tex2html_wrap_inline1881 tex2html_wrap_inline1911 tex2html_wrap_inline1913 tex2html_wrap_inline1901 K2
Table 1: Data for the variable, comparison, and check stars

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