Photometric Observations of an Extreme ER UMa Star, RZ Leonis Minoris

From the photometric monitoring of RZ LMi for 44 days between 1995 February 5 and March 20, we identified RZ LMi as an extreme ER UMa-type dwarf nova: a subclass of SU UMa-type dwarf novae. We give a definition of ER UMa stars and clarify the difference between ER UMa stars and ordinary SU UMa stars. The most conspicuous characteristic of ER UMa stars is their extreme short cycle length of superoutbursts (supercycle), which in RZ LMi is ~ 19 days. The superhump period of RZ LMi is 0.05946 +/- 0.00004 days. The peculiar light curve of ER UMa stars suggests an extraordinarily large mass-transfer rate among SU UMa stars, which can not be explained by the current scheme concerning the origin of mass-transfer of cataclysmic variables (CVs). Moreover, the high incidence of such systems among known CVs suggests that an important course of the evolution of CVs may have been overlooked.