Top: dynamical maps on the parametric plane Ω_p–ζ₀, defined by the pattern speed and the amplitude of the spiral perturbation (Eq. (5)), respectively. The maps were calculated for the initial conditions of the SSP and ϕ = 52° (left), ϕ = 142° (right), corresponding to the possible SSP azimuthal positions (see Sect. 7.3). The red crosses represent the location of the SSP according to the parameters used in this paper. The central light-coloured region corresponds to the stable co-rotation resonance. Bottom: same as in the top panel, except on the parametric plane Ω_p–ϕ, defined by the pattern speed and the azimuthal angle, respectively.