Radius of the escape sphere when drag is neglected. The minimum luminosity, k_esc, that unbinds a particle in circular orbit at x_esc is shown as a function of the initial orbital radius, for two values of initial luminosity, k₁ = 0.0, and 0.36. Stellar radius is X = 5.0. Constant k_esc lines represent Newtonian limit (NL) for k₁ = 0.0,0.36. If there were no drag, particles from all circular orbits of radii in the range 6 ≤ x(0) <x_esc(k_esc) would escape the system, and the initial radius in the outgoing trajectory, x(0), would be its periastron as well.