Top: surfaces of section on the ϕ–V_θ plane calculated along the energy level ℋ = −0.2298 kpc² Myr^-2, close to the SSP energy, and V_θ> 0. Several resonances appear as chains of islands (the number of islands is equal to the order of the resonance); some are indicated. The estimated values of ϕ for the SSP (52° or 142°, see Sect. 7.3) place it inside the co-rotation resonance (see also Fig. 13); the period of the J_ϕ-mode of oscillation of the SSP is about 2 Gyr. Bottom: same as the top panel, except that ℋ = −0.20 kpc² Myr^-2 and V_θ< 0.