Neutral sound speed (dotted) and neutral (dot-dashed) and ion (solid) magnetosonic speeds as functions of the UV radiation field in a medium of density n_H = 10² cm⁻³ and a visible extinction (upper left), and as functions of the transverse magnetic field intensity in a medium of density n_H = 10⁴ cm⁻³ and G₀ = 0 (upper right). All other parameters are set to their standard values (see Table 1). The critical velocities above which C-type shocks cannot exist are shown with red points, while coloured areas highlight the range of velocities at which C- (green), C*- (yellow), CJ- (violet), and J-type (blue) shocks develop.