V light curves of DI UMa

During quiescence, the light curve reveals a modulation of period P_orb_=0.054579(6)days (78.59+/-0.01min), which we interpret as the orbital period of the binary system. The values obtained allowed us to determine a fractional period excess of 1.35+/-0.02%, which is surprisingly small compared to the usual value for dwarf novae (2%-5%). A detailed O-C analysis was performed for two superoutbursts with the most comprehensive coverage.

In both cases, we detected an increase in the superhump period with a mean rate of (dP/dt)/P_sh_=4.4(1.0)x10^-5^. Based on these measurements, we confirm that DI UMa is probably a period bouncer, an old system that reached its period minimum a long time ago, has a secondary that became a degenerate brown dwarf, the entire system evolving now toward longer periods. DI UMa is an extremely interesting object because we know only one more active ER UMa star with similar characteristics (IX Dra).