where V b i n is the relative velocity of the two stars in the binary. The change in the field star's specific angular momentum with respect to the binary, l , is then Δ l ≈ a V bin. Conservation of angular momentum implies that the binary's angular momentum changes by Δ l bin ≈ -(m/μ 12)Δ l where m is the mass of a field star and μ 12 is the binary reduced mass. Changes in the magnitude of l bin correspond to changes in the binary's orbital eccentricity via the relation e = 1 - l b / GM 12 μ 12 a. Changes in the direction of l bin correspond to changes in the orientation of the binary, leading to rotational diffusion. The rotational diffusion coefficient is