2000NewA....5...53B

The effects of binary tidal forces on transport within an accretion disk are studied with a time-dependent hydrodynamical model of a two-dimensional isothermal accretion disk. Tidal forces quickly truncate the accretion disk to radii of order half the average radius of the Roche lobe, and excite a two-armed spiral wave that remains stationary in the rotating reference frame of the binary system. We measure an effective alpha of order 0.1 near the outer edge of the disk in all of our models, independent of the mass ratio of the binary system, the Mach number of the orbital motion in the disk, and the radial density profile of the disk. The value of alpha drops with decreasing radius, implying that steady-state models (constant mass accretion rate at all radii) do not exist. In cold disks with high Mach number, the effective alpha drops so rapidly that it falls below our threshold of measurement ( ∼ 10^ - 3) at a radius of only one third the tidal radius. In warmer disks where the Mach numbers remain below 20, we can measure an effective alpha down to radii 10 times smaller than the maximum size of the disk.