Long-lasting growing superhumps in SU UMa stars: QZ Vir

Abstract

We report on the 2015 February-March superoutburst of the well known SU UMa-type dwarf novae QZ Vir (= T Leo). The light curve showed a unique feature in which the precursor was completely separated from the main superoutburst. During the stage between the precursor and main superoutburst, we detected superhumps with the mean period of 0.061181(42) d. Based on the amplitudes and $O - C$ analyses of superhumps, we identified the observed superhump during the faint stage as stage A superhumps. Using the orbital and stage A superhump period of QZ Vir, we derived the mass ratio to be 0.108(3). This value indicates that the system is an SU UMa-type dwarf novae evolving toward the period minimum. Here we briefly discuss that long-lasting growing superhumps can offer an opportunity to examine the evolutional status of SU UMa-type dwarf novae with moderate orbital periods, and future strategies of photometry of SU UMa-type dwarf novae.