Discovery of a New ER UMa-Type Dwarf Nova IX Draconis

We observed a new dwarf nova, IX Dra, for 46 days between 2000 November 10 and 2001 June 17, and revealed that IX Dra is the fifth member of a peculiar group of SU UMa stars, called ER UMa stars. The light curve is almost perfectly identical to that of V1159 Ori: supercycle, 53 d; interval of normal outbursts, 3–4 d; duty cycle, ∼ 30%; and the outburst amplitude, 2.5mag. From a time-series observation during the superoutbursts, we obtained a presumable superhump period of 0.067 d. We note that some clustering may exist in the period distribution of ER UMa stars. It is needed to confirm this clustering by a larger number of examples.