Binaries traveling through a gaseous medium: Dynamical drag forces and
  internal torques
  Using time-dependent linear theory, we investigate the morphology of the
gravitational wake induced by a binary, whose center of mass moves at velocity
Vcm against a uniform background of gas. For simplicity, we assume that the
binary's components are on circular orbits about their common center of mass.
The consequences of dynamical friction is twofold. First, gas dynamical
friction may drag the binary's center of mass and cause the binary to migrate.
Second, drag forces also induce a braking torque, which causes the orbits of
the binary components to shrink. We compute the drag forces acting on one
component of the binary due to the gravitational interaction with its own wake.
We show that the dynamical friction force responsible to decelerate the
binary's center of mass is smaller than it is in the point-mass case because of
the loss of gravitational focusing. We show that the braking internal torque
depends on the Mach numbers of each binary component about their center of
mass, and also on the Mach number of the center of mass of the binary. In
general, the internal torque decreases with increasing the velocity of the
binary relative to the ambient gas cloud. However, this is not always the case.
We also mention the relevance of our results on the period distribution of
binaries.
