ИСТИНА

EX Dra is one of a few double eclipsing cataclysmic variables (CVs) that exhibits eclipses of the white dwarf and of the hot spot. It is a U Gem-type dwarf nova above the 2 − 3 hours period gap. During monitoring this dwarf nova photometrically in Rc band, we showed that it was undergoing frequent outbursts and three outbursts were observed. During the outbursts, the brightness increases more than 1.4 magnitude and the time interval between two outbursts is about 16 days. The hump in an outburst light curve disappears and a V-shaped eclipse feature appears. By using some mid-eclipse times determined with our data and those compiled from the literature, the changes in the orbital period were analyzed. It is shown that the variations in the O-C curve are very complex and physical mechanisms that may cause those changes were discussed.