On the dynamics of mass transfer over an accretion disk

Abstract

We analyze the vertical dynamics of a gas stream as it flows over a disk in a semidetached binary. For plausible parameters, the gas stream at several scale heights above the binary orbit plane is able to flow over the disk once it passes the disk edge. Relatively high, free-flowing gas collides with the disk near the stream's closest approach with the compact object. We identify the resulting emission with a feature found in the Doppler tomography of dwarf nova Z Cha. These results can also explain the origin of asymmetric emission lines in other dwarf novae and dips in low-mass X-ray sources.