2012MNRAS.427..581R

Fine-structure mid-infrared emission lines with critical densities in the regime 10⁴ ≤ n_crit ≤ 10⁶/cm3 can be employed to probe the outflow from Wolf–Rayet (WR) stars at radii of ∼ 10¹⁵cm. Narrow-band mid-infrared imaging and spectroscopy of the nearest WR star to the Sun, γVelorum is analysed for spatially resolved forbidden line emission in the WR outer wind. The [SIV] 10.52-µm and [NeII] 12.81-µm emission regions are found to be spatially extended, compared to unresolved continuum and He and C recombination line emission. The [SIV] and [NeII] 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 ∼ 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/r² outflow with constant ionization fraction and modestly clumped density structure.