On possible observational evidences of spiral shocks in accretion disks of CVs

The results of three-dimensional numerical simulations of mass transfer in binaries with spiral shocks are presented. It is shown that the mass transfer rate variation disturbs the equilibrium state of accretion disk and results in formation of the blob. This dense formation moves on the disk with variable velocity. The results of our simulations show that the blob lives long enough and retains its main characteristics for the time of order of tens orbital periods. Analysis of the results shows that the action of dissipation is negligible on these timescales and the blob smearing out due to differential rotation of the disk is stopped by its interaction with spiral shocks. Light curves of some CVs show periodic or quasi-periodic photometric modulations with typical width ∼ 0.1÷0.2 (i.e. with period ∼ 0.1÷0.2Porb). We suggest to consider the formation of the blob in binaries with spiral shocks as a possible reason for these modulations. The efficiency of this mechanism is confirmed by good qualitative (and, in part, quantitative) agreement between the results of our simulations and observations of binaries IP Peg and EX Dra.