Both presentations of the results (Table 3 (click here) and corresponding figures) show that in the case of the Roche model with two spotted regions, the synthetic light curves obtained by solving the inverse problem fit the observations very well (almost within the measurement accuracy). The variations of the basic system parameters among the different curves for the analysed period are insignificant. This means that the variations in the light curves can be explained by the change of the position and size of the spotted areas on the primary.
For the majority of the analysed light curves the single spot model (Table 2 (click here) and corresponding figures) fits well the observations. But this model requires comparatively large variations of the basic system parameters (e.g. the stellar size - Fig. 2b) during the analysed period. Therefore, we tend to exclude this solution.
Appearing at high latitudes, the spotted areas cover a significant part of
the stellar surface. Since the system's period is short 
, the
presence of spots at high latitudes (near the pollar regions) can be
explained by the dynamo mechanism for rapid rotators
(Schüssler & Solanski
1992).
In favour of presence of spotted areas at high latitudes we have an independent
argument based on the differential-rotation effect. As seen from the Fig. 2e,
and Fig. 3, the light curve depression is shifted through the orbital phase
with time. This depression migration can be explained by the difference
between the spotted area angular velocity 
and the Keplerian angular
velocity in the system's revolution 
. This is to be expected in the
case of the differential rotation of the stellar surface layers and for the
nonsynchronous rotation of the components. Here a short-period CB is
analysed whose stars fill in their critical Roche lobes significantly; hence
due to the tidal effects the rotation of the components is expected to be
synchronous.
The depression shifting along the light curves can be in both senses, direct and retrograde (see Busso et al. 1984), which depends on whether the spotted area latitude exceeds the corotational one or not. This circumstance (shifting sense) appears as a serious indication in favour of the diferential rotation existence. By applying simple approximations, based on the analogy with the problem of the differential rotation of the Sun, it is possible in certain cases to obtain the data on the component differential rotation in RS CVn type of CBs. Following the idea applied by Busso et al. (1985) the active region is approximated here by a circular spotted area whose centre corresponds to the photocentre of the given region and the photometric time variations of the light curves are interpreted through the change in the position and size of the spot. Due to the meridional motion from higher towards lower latitudes, the differential rotation causes the shift of the spotted area longitude in the course of time. The differential-rotation parameters are derived on the basis of these longitude shifts.
The single spot model is compatible with that for obtaining the
differential-rotation parameters. Although it has been shown that this model
has certain drawbacks, in analysing the differential rotation one can
exploit the data of the spotted area longitudes (see Table 2 (click here)) for the entire
set of observed light curves over the interval 1973-1981. Such an analysis is
presented in
Djurasevic (1996). The nonlinear system of equations,
describing the differential rotation is solved following adequate approaches
(Marquardt's algorithm - Marquardt 1963 - and SIMPLEX -
Torczon 1991).
These algorithms are suitable for the problems of nonlinear optimisation and
they enable one to solve equation systems describing the differential
rotation. The results obtained for the case of SV Cam
(Djurasevic
1996) indicate that the spotted area appears at high latitudes (about 
),
whereas the corotation latitude is about 
. Although the model for
calculating the differential-rotation parameters is rough, this result is an
indication that in the case of the short-period RS CVn type of CBs,
spotted areas can be expected in the polar regions.
The consideration of the differential rotation problem and the results of the light curve analysis for SV Cam presented here, clearly indicate that large spotted areas in the polar regions of the primary could be accepted as a reality.
Acknowledgements
This work has been supported by the Ministry for Sciences and Technology of Serbia through the project "Astrometrical, Astrodynamical and Astrophysical investigations".