Astron. Astrophys. Suppl. Ser. 131, 17-23

Analysis of the activity of the eclipsing binary WZ Cephei

G. Djurasevic¹ - M. Zakirov² - A. Hojaev² - G. Arzumanyants ²

Send offprint request: G. Djurasevic

1 - Astronomical Observatory, Volgina 7, 11050 Belgrade, Yugoslavia
e-mail: gdjurasevic@aob.bg.ac.yu
2 - Astronomical Institute of Uzbek Academy of Sciences, Astronomicheskaya 33, 700052, Tashkent, Uzbekistan

Received September 18, 1997; accepted January 28, 1998

Abstract:

The present study deals with the problem of the orbital and physical parameters' estimation of the active eclipsing binary WZ Cep based on the interpretation of its photometric observations. The B and V light curves (Hoffmann 1984), as well as the new ones obtained at the Maidanak Observatory in the B, V and R passbands during 1995, are analysed and discussed. These two groups of light curves show large differences in their shape and in the depth of the primary minimum. Hoffmann's light curves show big asymmetry, especially conspicuous in the different height of the successive maxima. The new observations give light curves that are almost symmetric having significantly shallower primary minimum.

They are analysed in the framework of the Roche computer model (Djurasevic 1992a) by applying the inverse problem method (Djurasevic 1992b) based on Marquardt's (1963) algorithm. The model is generalised for the case of an overcontact configuration also. To explain these light curves asymmetries and variations, the model involved spotted regions on the components. The analysis shows that WZ Cep system is in a slight overcontact configuration and that best fitting is achieved with spotted regions on the primary star (SpF5), with the temperature contrast between the spotted area and the surrounding photosphere being $A_{\rm s}=T_{\rm s}/T_1\sim0.70$. The mass ratio was estimated at the value $q=m_2/m_1\sim0.33$, based on the light-curve analysis.

The basic parameters of the system and of the spotted areas are estimated for all foregoing mentioned light curves. The obtained solutions show that there are no significant variations of the system's basic 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 the size of the spotted areas on the primary.

Key words: stars -- activity -- W UMa type -- eclipsing binaries-stars -- individual -- WZ Cep