Series of closed orbits in the plane of the Galaxy obtained using the rotation curve of Eq. (17). The spirals indicated in green represent the imposed perturbation; they coincide with the response density (red dots) up to 4:1 resonance. The red circle is the corotation radius (R_cor = 8.4 kpc). The perturbation amplitude is ζ₀ = 600 km² s^-2 kpc^-1. The yellow dot shows the Sun position.