Discovery of a New SU UMa Star, CI Ursae Majoris

We detected superhumps with a period of 0.0625 (±0.0007) d in CI UMa during a bright outburst in 1995 January. From this, CI UMa was first proven to be a SU UMa-type dwarf nova. We found the interval of the superoutburst to be about 140 d from historical records of the outburst. If this represents the cycle length of the superoutburst (supercycle), CI UMa has the third-shortest supercycle among usual SU UMa stars, except for ER UMa stars. We regard CI UMa as being an intermediate object between ER UMa stars and the usual SU UMa stars based on the short orbital period estimated from the superhump period and the short supercycle. It may be crucial to clarify whether the supercycle has changed by closely monitoring CI UMa in order to solve any problem concerning the evolutionary path of ER UMa stars.