1 Introduction

The binary AU Ser was observed visually and photographically by Soloviev (1951) and Huth (1964) respectively. The first photoelectric observations were performed by Binnendijk (1972). Hrivnak (1993) obtained its radial velocity curve using the cross-correlation technique. Kaluzny (1986) analyzed Binnendijk's data. The pronounced asymmetry in the light curves was attributed to the effect of a hot spot located at the neck between the components, and the points in the phase interval between 0.08 and 0.46 were rejected from his analysis. AU Ser was identified as a poor thermal contact binary predicted by the thermal relaxation oscillation (TRO) theory of Lucy & Wilson (1979). For the same observational data, on the other hand, Djurasevic (1993) assumed that the asymmetry is due to RS CVn-type activity and he obtained a detached photometric solution. Obviously, these assumptions leading to very different solutions must be more sufficiently justified. For this reason more observations are necessary before modeling.

AU Ser has been photoelectrically monitored for five years. In this paper we report the results of these observations. A description of the observations is given in the next section; In Sects. 3 and 4 we show the variations in period, light curves and color curves, respectively. The finding of short period oscillations is described in Sect. 5. Finally we summarize the results.