Formation of the "precessional" spiral wave in the cool accretion disk in semidetached binaries

We suggest that an additional spiral density wave can exist in the inner parts of the cool accretion disk, where gas-dynamical perturbations are negligible. This spiral wave is due to the retrograde precession of the streamlines in the binary system. The results of a three-dimensional gas-dynamical simulation have shown that a considerable increase in the accretion rate (by an order of magnitude) is associated with the formation of the "precessional" spiral wave. Basing on this fact we suggest a new mechanism for the superoutbursts and superhumps in binaries.