Photoelectric photometry of the unusual eclipsing binary system FF Aquarii

FF Aqr is the first eclipsing binary (P = 9 d .2) containing a hot subdwarf (sdOB) and a chromospherically active cool giant component classified as a G8-K0 III star. We observed the system in U, B, V and R filters during 2002, 2003 and 2004 observing seasons using two di erent telescopes and detectors. We obtained a total of 1171 observational points in each colour. The light curve reveals that FF Aqr has a totality in the primary eclipse, which lasts about 13 h 02 m . The shape of the light curve indicates that FF Aqr is an Algol type binary. The light curves display an asymmetrical wave-like distortion at outside of the eclipse which has a minimum at about 0 P.46 and a light amplitude of 0 m .050, 0 m .204, 0 m .277, 0 m .282 in the U, B, V, and R bands, respectively. This variation can not be explained by the reflection e ect alone. We used the Wilson-Devinney code for the geometric and physical parameters of the system. The asymmetry at outside of the eclipse light variation and the results obtained from the light curve analysis were discussed.