Contour lines showing the dependence of obscuration on mass-loss rate and binary separation, for photons emitted at 350 eV. The left-most solid line corresponds to an attenuation factor of 5, the dotted line to an attenuation of 10, dashed to an attenuation of 100, and dot-dashed to an attenuation of 1000. The right-most solid line is the critical mass-loss rate Ṁ_Str; to the left of this line, the wind is insufficiently dense to sustain a clearly defined ionized region around the source. To the right of it, a clearly defined ionized region exists around the source, while the material outside of this region is neutral.