Left: dynamical map of the neighbourhood of the co-rotation point calculated with the variables p_R and ϕ fixed at zero. The red cross shows the position of the SSP integrated backwards until p_R = 0. Right: same as in the left graph, except ϕ = 90°. Comparing the graphs, we note that the star would be inside the co-rotation resonance island or in a very chaotic area, depending on the angle ϕ.