Dynamical Friction and Tidal Interactions
  We discuss dynamical friction in an $N$-body system in the presence of tidal
interactions caused by a distant external source. Using the distant tide
approximation, we develop a perturbation scheme for the calculation of
dynamical friction that takes tidal effects into account to linear order. In
this initial analytic approach to the problem, we neglect the influence of
tides on the distribution function of stars in the background stellar system.
Our result for the dynamical friction force in the appropriate limit is in
agreement with Chandrasekhar's formula in the absence of tides. We provide
preliminary estimates for the tidal contributions to the dynamical friction
force. The astrophysical implications of our results are briefly discussed.
