First-order streamlines. Shown are contours of constant f₂   r² + f₁   r, for the case β = 1.1 . The dotted, diagonal lines trace the Mach and anti-Mach cones, while the central, dotted circle is r/r_s = 1 . Within the intermediate region, the dashed streamlines were constructed assuming C =  −1 . The solid ones correspond to C =  +1and are more realistic.