Isocontours of the collisional term S ₀/( f ₀ξ) in the space of orbital elements. Horizontal dashed line corresponds to the mean eccentricity of particle orbits in the initial model. Mass parameters have been set to μ = 0.04 and μ _p = 1/8. Particles migrate linear in time toward the accumulation point ( a ₀, e ₀) ≈ (0.63, 0.128) shown by a cross. Contour lines mark the levels 0.0 to 4 × 10 ⁻⁴ with steps of 10 ⁻⁴. Note the logarithmic scale of the a-axis.