Sketch of the model consisting of a conical lobe intersected by the plane of the disk. The axis of the cone coincides with the z axis and the plane contains the y axis. The black lines are the intersections between the plane and the cone, while the red lines are their projections onto the x, y plane. Also indicated are the angle ψ₀ between the plane x, y and the plane of the disk, the opening angle θ₀ of the cone, and the angles ϕ_± between the x axis and the red lines.