The location of the 3:1 resonance as a function of binary mass ratio (red dashed lines, Equation (11)). The contours show the forcing term, s (Equation (10)), for disk aspect ratios of H/r = 0.01 (left), 0.03 (middle), and 0.05 (right). The solid orange lines show a typical location of the disk outer radius for a tidally truncated disk at r_out = 0.9 r_l.