Abstract

We report here on time-resolved photometric observations of the superoutburst of a dwarf nova, RZ Leo, which occurred during 2000 December-2001 January. We reveal the following characteristics of the outburst based on our observations: long duration, large amplitude, and the existence of two types of superhumps - "early superhumps" and "normal superhumps". In addition to the extremely low frequency of the outbursts, the characteristics of the outburst strongly indicate that RZ Leo is the fifth member of the WZ Sge-type dwarf novae. The orbital period of RZ Leo is 0.07651 d, which is remarkably longer than the "canonical" period of other WZ Sge stars (? 0.058 d). The longer period indicates a non-degenerate secondary of RZ Leo, which suggests that the idea of a low quiescence viscosity due to a degenerate brown dwarf secondary may not be correct. The present discovery of RZ Leo as being a WZ Sge star provides the first clear indication that the decay of magnetic turbulence in accretion disks of quiescent WZ Sge stars plays an important role in producing the proposed low quiescent viscosity.