1 Introduction

The eclipsing binary WZ Cep is a short period ($P=0\hbox{$.\!\!^{\rm d}$}417447$)system showing an EB-type light curve. According to the General Catalogue of Variable Stars - GCVS (Kholopov et al. 1985) the spectral type of the system is F5. Photoelectric observations (Hoffmann 1984) show a high degree of asymmetry of the light curve. Namely, the primary maximum (phase 0.25) is significantly higher than the secondary one. In Balazs' (1937) and Detre's (1940) observations we can find the changes in the light curve shape and the depth of successive minima. New photoelectric observations, obtained at the Maidanak Observatory during 1995, show that the light curve of WZ Cep dramatically changed its shape. Compared with Hoffmann's light curve, the depth of the primary minimum is significantly lower and the light curve is quite symmetric. This variability in the light curve form may be attributed to a variable star spot activity and to a variable level of the energy transfer between the components.

By analysing Hoffman's observations with the Wilson-Devinney method Kaluzny (1986) obtained the solutions that WZ Cep is in the overcontact configuration with the components having significantly different effective temperatures. He concluded that observed light curves (with large degree of asymmetry) can be reproduced theoretically if one assumes the existence of a relatively small hot spot region placed on the less massive component, near the neck between stars.

The reanalysis of this observational material in the frame of Roche computer model (Djurasevic 1992a) generalised to the case of the overcontact configuration showed that the hot spot hypothesis cannot offer a satisfactory solution. Moreover, the analysis of Hoffman's and new observations presented in this paper proved that the changes in the light curves of WZ Cep are caused by the presence and the development of the dark spotted areas on the system's components. This type of activity is relatively well established within great number of stars with convective envelopes. Based on the spectral type (F5) and the solutions obtained by analysing the light curves we think that the WZ Cep system exhibits this type of activity also.