1. 1 Astronomical Observatory, Volgina 7, 11160 Belgrade, Serbia & Montenegro 2 Isaac Newton Institute of Chile, Yugoslav branch 3 Institute of Astronomy, Bulgarian Academy of Sciences, Tzarigradsko Chosse 72, 1784 Sofia, Bulgaria 4 Ankara University, Faculty of Science, Department of Astronomy and Space Science, 06100 Tandogan, Ankara, Turkey e-mail: gdjurasevic@aob.bg.ac.yu A study of close binary system EE Cet G. Djurašević 1,2, D.Dimitrov 3, B.Arbutina 1, B.Albayrak 4, and S.O.Selam 4

2. Close binary EE Cet W UMa-like stars W UMa-like stars are the most common systems among the contact binaries. They range from late F stars to K stars and are characterized by common convective envelope. There are actually two subtypes of the W UMa-type systems: A-type and W-type. In the A-type systems the deeper primary minimum represents a transit, while in the W case it is an occultation. The temperature of the secondary star is in both cases typically higher that the value we would expect if the secondary was to be a single star. This is because the temperatures correspond to the common envelope. W UMa-type systems show evi- dence for mass and energy transfer (loss) - e.g. enhanced temperature in the neck region, and magnetic acti- vity - the presence of starspots. min I W O B A F G K M A

3. Close binary EE Cet Case study: EE Cet EE Cet is a W-subtype of the W UMa-type binary systems. It has been discovered as a variable star in the Hipparcos mission. We have com- bined our photometric with earlier spectroscopic observations of Rucinski et al. (2002) to derive the following physical parameters of the system: comp.12 T eff [K]60956305 M [ M Ÿ ]1.370.43 R [ R Ÿ ]1.350.82 The system has the inclination i=79 o. All the parameters are obtained by using the numerical codes of Djurašević (1992a,b) and Djurašević et al. (1998). A slight assymetry of the light curves can be explained with the presence of the cool spot at the primary compo- nent. min I min II Spectroscopic obs. Rucinski et al. (2002) Photometric obs. Djurašević et al. (2005) F8 V W-type

4. Close binary EE Cet ADS 2163 – a quadruple system ! EE Cet is the southern binary component in the visual-spectro- scopic triple system ADS 2163. Due to the proximity of the visual companion separated by 5”.6, our light curves were contaminated by the third light. Moreover, it was found that the northern component is also a close binary showing radial velocity variations, thus turning ADS 2163 into a quadruple system. Future studies of EE Cet and its northern companion would therefore be particulary interesting and will be necessary in order to provide us with more accurate information on this quadruple system and its com- ponents. 5th SCSLSA Vrsac 2005 barbutina@aob.bg.ac.yu EE Cet Eclipsing binary Spectroscopic binary ? ADS 2163