The dwarf nova RZ Leonis: photometric period, "anti-humps" and normal alpha disc

We present results of differential photometry of the dwarf nova RZ Leonis s panning a 11-year baseline. The most striking feature of the light curve is a non-coherent periodic hump of variable amplitude. A seasonal time series analysis yields a photometric period of 0.(d)0756(12). In addition, low am plitude fluctuations of the mean magnitude in time scale of months are obse rved. We find that the hump's amplitude is anti-correlated with the star's mean magnitude and becomes "negative" (i.e. an absorption feature or "anti- hump") when the system is very faint. Secondary humps and "anti-humps" are also observed. The transition from "anti-humps" to fully developed humps oc curs on a time scale of 70 days. We interprete the observations as a rapid response of the accretion disk to the increase of mass transfer rate. In th is case we deduce a viscosity parameter alpha similar to 0.08, i.e. much la rger than often claimed for WZ Sge-like stars. We note that the secondary s tar in RZ Leo is close to a main-sequence red dwarf and not a brown-dwarf l ike star as suggested for other long cycle-length SU UMa stars like WZ Sge and V592 Her. Our results indicate that large amplitude and long cycle leng th dwarf novae might not necessarily correspond to objects in the same evol utive stage.