Neutral sound speed (dotted) and neutral (dot-dashed) and ion (solid) magnetosonic speeds as functions of the density (upper left panel), transverse magnetic field intensity (upper right panel), UV radiation field intensity (lower left panel), and visual extinction (lower right panel). All the non-varying parameters are set to their standard values (see Table 1), and the standard value of the buffer visual extinction is set to . 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.