On the nature of superoutbursts in dwarf novae

We present the first detailed hydrodynamic simulation of a superoutburst to incorporate the full tidal potential of a binary system. A two-dimensional smoothed particle hydrodynamics code is used to simulate a superoutburst in a binary with the parameters of the SU UMa system Z Chamaeleontis. The simulated light curves shows all the features observed in such systems. Analysis of the mass flux through the disc and the growth rate of the superhumps and disc eccentricity show that the superoutburst–superhump phenomenon is a direct result of tidal instability. No enhanced mass transfer from the secondary is required to initiate or sustain these phenomena. Comparisons of superoutbursts with normal outbursts are made and we show that the model can be reconciled with the behaviour of U Geminorum-type dwarf novae, which show no superoutbursts.