Value of f(ξ = 0, χ) as a function of χ—the fraction of passing through the orbit of the secondary. Different curves correspond to different values of the power-law parameters d and p indicated in the figure: dotted lines correspond to the gas pressure-dominated case with κ = κ _es, and solid lines correspond to the gas pressure-dominated case with κ = κ _ff. Knowledge of f(ξ = 0) permits a computation of the torque acting on the central binary for an arbitrary value of the "accretion fraction" χ.