Evolution of negative superhumps

A photometric study of the negative superhumps for three SU UMa-type dwarf novae MN Dra, NY Her and V503 Cyg is presented. It is based on intensive observations from 2012 to 2018 obtained at five observatories. These dwarf novae are known as systems with strong variations (two to three times) of the interval between successive normal outbursts (cycle) and superoutbursts (supercycle). The negative superhumps were recorded with an increased cycle. We investigated the evolution of negative superhumps on a long time scale and revealed systematic changes in the periods of negative superhumps during the cycle and supercycle that are identical for the three systems. These variations may indicate changes in the radius of accretion disk between outbursts and superoutbursts. We found that the observed variations fit with a prediction of the thermal-tidal instability model of the superoutburst and supercycle of SU UMa-type dwarf novae.