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Tidally-Driven Transport in Accretion

Disks in Close Binary Systems
John M. Blondin

North Carolina State University

Manuscript submitted to
New Astronomy
on August 27, 1999

Accepted January 3, 2000

### ABSTRACT

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, Mach number,
and radial density profile. However, in cold disks with high Mach number,
the effective alpha drops rapidly with decreasing radius such that
it falls below our threshold of measurement (of order .001) 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.