Corotation zones originated by the four-arm spiral perturbation, with Ω_sp = 28.5 km s⁻¹ kpc⁻¹ (black), and by the central bar perturbation, with Ω_bar = 40.0 km s⁻¹ kpc⁻¹ (red). The different pattern speeds were chosen with the purpose of showing each contribution separately. The values of other parameters were taken from Table 1. The zone of influence of the bar is centred at the origin; the directions of the major and minor axes of the bar are shown by dashed lines. The positions of the stable corotation centres are shown by dots, while the positions of the unstable saddle points are shown by crosses (see text for details). The position of the Sun is shown by a blue cross symbol.