The Outer Wind of gamma Velorum

TL;DR

This study uses mid-infrared emission lines to analyze the outer wind of gamma Velorum, revealing a spherically symmetric, clumped, freely expanding outflow consistent with a 1/r^2 density profile.

Contribution

First spatially resolved mid-infrared analysis of gamma Velorum's outer wind, demonstrating the wind's spherical symmetry and the importance of clumping in modeling.

Findings

Emission lines are spatially extended and azimuthally symmetric.

Clumped wind models fit observations better than unclumped models.

The wind exhibits a 1/r^2 density profile with constant ionization.

Abstract

Fine-structure mid-infrared emission lines with critical densities in the regime 10^4 to 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 and [Ne II] 12.81 micron 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.