Constraints from ISO Data on the Velocity Law and Clumpiness of WR 136

Abstract

Observations with the Infrared Space Observatory (ISO) SWS spectrometer are used to constrain the velocity law and wind clumping of the well-studied Wolf-Rayet (WR) star WR 136 (HD 192163) (WN6). Because the free-free continuum opacity in WR winds increases steadily with wavelength in the IR, each point in the continuous spectrum may be regarded as forming in a pseudo-photosphere of larger radius for longer wavelength. Using this idea in combination with an analysis of the Doppler-broadened widths of several \ion{He}{2} recombination lines, we can derive information about the velocity law and clumpiness of the stellar wind of WR 136. Adopting a \(\beta\)-law distribution for the outflow velocity law, we compute the continuous energy distribution and line profiles. Interestingly,the continuum data are found to constrain the wind to have fairly low clumping values for the IR-forming region.