Energy Change in a Hard Binary Due to Distant Encounters

An approximate analytical technique for computing the change in the binding energy of a binary due to an incoming third star moving in a distant parabolic orbit is presented. This is an example of a tidal encounter since we assume that the distance of the third star always considerably exceeds the size of the binary. The perturbation is also adiabatic, varying on a time scale much exceeding the binary period, and the change has an exponential form. Different cases arise depending on the choice of the masses and the angle of inclination of the plane in which the star moves. Some numerical experiments are performed as a means of checking the analytical theory.