Fine-structure mid-infrared emission lines with critical densities in the regime 10 ^ { 4 } \leq n _ { crit } \leq 10 ^ { 6 } cm ^ { -3 } can be employed to probe the outflow from Wolf-Rayet stars at radii of \sim 10 ^ { 15 } cm .
Narrow-band mid-infrared imaging and spectroscopy of the nearest WR star to the sun , \gamma Velorum is analysed for spatially resolved forbidden line emission in the Wolf-Rayet outer wind .
The [ S iv ] 10.52- \mu m and [ Ne ii ] 12.81- \mu m emission regions are found to be spatially extended , compared to unresolved continuum and He and C recombination line emission .
The [ S iv ] and [ Ne ii ] emission line distributions have a high degree of azimuthal symmetry , indicating a spherically symmetric outflow .
A model wind with a modest degree of clumping ( clumping factor f \sim 10 ) provides a better match to the observations than an unclumped model , The overall line intensity distributions are consistent with a freely expanding , spherically symmetric 1/ r ^ { 2 } outflow with constant ionization fraction and modestly clumped density structure .