SPH Simulations of Early and Late Superhumps

Abstract

AbstractSmoothed particle hydrodynamics is a Lagrangian method for the solution of the hydrodynamic equations. Here this method is used to simulate the accretion disk in dwarf novae with very low mass ratio, q < 0.25, typical for SU UMa-type systems where the accretion disk can become eccentric and precessing during a superoutburst, leading to periodic brightness variations, so-called superhumps. Two phenomena are examined. First the late superhumps, i.e., the occasional persistence of superhumps well after the return to quiescence, seen e.g. in OY Car and IY UMa. This is due to a varying brightness of the hot spot region, as the eccentric disk continues to precess in quisecence. Second, the occurence of early superhumps in the superoutburst of WZ Sge. Tidal forces compress the rim of the disk, the tidal dissipation leads to a double-peaked strucure in the orbital light curve during the early stage of the superoutburst.