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.