4 Discussion and conclusions

Both presentations of the results (Table 2 and corresponding Figs. 1 and 2) show that within the Roche model with spotted regions on the primary, the synthetic light curves obtained by solving the inverse problem fit the observations very well (almost within the measurement accuracy). The obtained solutions show that there are no significant variations of basic system's parameters estimated by analysing these two groups of very different light curves. Consequently, the main variations in the light curves can be explained by the change of the position and size of the spotted areas on the primary. Although a very rough approximation of the possible real processes in the WZ Cep system was applied in this analysis, the model could successfully simulate the observed light curves. By that we obtained a quite good agreement between the solutions in the analysis of individual light curves in different filters of the photometric system.

The solutions presented above show that WZ Cep is in the slight overcontact configuration $(f_{\rm over}[\%] \sim 10\%-15\%)$, with small temperature differences between components $(\Delta T=T_1-T_2\sim140- 170 \ \rm K)$. Since the mass ratio is estimated about $q=m_2/m_1\sim0.33$, this suggests a significant energy transfer from primary to the less massive secondary component. Having in mind the large changes in the shape of the light curves, the future photometric observations of this interesting system are of great interest. The radial velocity curves are also necessary for more reliable estimation of mass-ratio.

The problem of the uniqueness of obtained solutions remains open to some degree. Our tests with different working hypotheses show that the results presented here give the best fit of the observations. However, in principle, in double spot models one can expect a non uniqueness in estimating of the spot's parameters. To solve the problem of the surface brightness distribution, the photometry must be coupled with other data in the future. Doppler stellar tomography based on the spectroscopic observations is very promising way to solve this problem. Such spectroscopic observations require the use of large telescopes (high spectral resolution and high signal to noise ratio). The use of an independent method is necessary to test validity of the results obtained through the analysis of the light curves.

Acknowledgements

The authors sincerely thank N.R. Bairamov, V.V. Ignotova and R.Ya Ishankulov for their help and participation in the observations of WZ Cep. One of us (G.D.) has been partially supported by the Ministry of Sciences and Technology of Serbia through the project "Astrometrical, Astrodynamical and Astrophysical investigations".