XY UMa (=HD 27143 = BD +55 1317 = BV31) was firstly noted by Geyer et al. (1955) as an eclipsing binary with a period of . After which Geyer began a prolonged series of photometric observations, the results of which he reported in 1976, 1977, and 1980. He found that the revolution period of was constant during 20 years (15250 epochs!), and that the average brightness of the binary system changed between 1955 and 1975 in a sinusoidal manner by 0.18 mag in V and 0.20 mag in B, indicating a periodic variation of about 28 to 30 yrs. He gave a general explanation of the peculiarities of the photometric light curves of the system following as: the primary component shows a larger star-spot activity, the cycle of which is about 15 yrs (or double that value). So, he held responsible this star-spot activity for the observed asymmetrical light curves. Furthermore, carrying out spectroscopic observations of the system, he gave that the spectral classes of the components of XY UMa as G2-G5V+K5V. He also stated that both component are well below their Roche limit configuration. And then, the star was classified as a cool, "short period RS CVn'' star by Baliunas & Vaughan (1985). Indeed, XY UMa, in terms of its chromospheric surface flux, may well be the most active of such systems (Gurzadyan 1987).
During the last decade XY UMa attracted the interest of many observers: the system has been observed intensively in optical (e.g. Geyer 1980; Zeilik et al. 1982; Jassur 1986; Heckert & Zeilik 1988; Qisheng et al. 1989; Zeilik et al. 1988; Hilditch & Bell 1994; Jeffries et al. 1995), radio (Drake et al. 1986; Morris & Mutel 1988), infrared (Arevalo & Lazaro 1990; Mitrou et al. 1996), ultraviolet (Geyer & Hoffmann 1981) and X-ray (Bedford & Geyer 1986; Bedford et al. 1990; Dempsey et al. 1993) domains. Some polarimetric (Geyer & Metz 1977), spectroscopic (Budding & Kadouri 1982; Huisong & Xuefu 1987; Rainger et al. 1991) investigations have also been performed. Gurzadyan & Cholakyan (1995) investigated the magnesium (MgII) luminosities of XY UMa and other RS CVn stars which have been observed by Dempsey et al. (1993), and concluded that the main contribution in the magnesium emission in RS CVn type systems has purely intercomponent origin.
At least five diagrams have been published up-to-date (Geyer 1977; Lorenzi & Scaltriti 1977; Hall & Kreiner 1980; Lee 1985; Pojmanski & Geyer 1990). Each one shows a large scatter up to a value of . Geyer (1977) noted that the period of the system seemed to be constant. However some quadratic terms in ephemeris were introduced by Hall & Kreiner (1980, ) and Qisheng et al. (1989, ). Hall & Kreiner attributed the long-term variations to the mass-loss from the system. Pojmanski & Geyer (1990) showed that the residuals are strongly correlated with the asymmetry of the light curve (difference between the heights of the maxima was used as its measure) and concluded that the possible explanation for variation of the system XY UMa is the hypothesis of a third-body with 0.28 dwarf) revolving around the close binary. The main difficulty remained unsolved in their work, however, is how could the light-time effect be held responsible from the asymmetry seen in the light curves by ignoring the star-spot activity.
Light curve solutions of the system have been obtained by Geyer (1980), Jassur (1986), Budding & Zeilik (1987), and Banks & Budding (1989) from visible photometry, and Arevalo & Lazaro (1990) from infrared photometry. Many of them analyzed their light curves using the Budding (1977) method and concluded that the large light curve changes of XY UMa is due to stellar star-spot activity of the primary component of this binary.