2000A&A...353..624M

We present a detailed spectroscopic study of the WN8(h)+B0.5V binary system WR147 using a non-LTE model that incorporates advances in line blanketing and allows for clumping in the wind. Ground-based optical and near-infrared observations, and high-resolution spectra obtained with the ISO Short Wavelength Spectrometer are combined for this study. Previously derived interstellar extinction values of E_B–V≃4.1mag at R_V≃2.7 are confirmed here. The distance to WR147 is revised slightly upwards to 650pc, based on Galactic and LMC WN8-9 calibrators in the K band. An infrared extinction curve for this sightline reveals absorption bands at 9.7 and 18µm that are stronger than expected for the average ISM, but the nature and location of the intervening material is unknown. He line profiles of the WN8 star exhibit clear evidence for clumping in the wind. We find that a volume filling factor f of 0.1 yields line profiles which match observations (emphasizing the electron scattering wings), though values of f in the range of 0.04 to 0.25 are reasonable. This leads to a mass-loss rate range of (1.5-3.7)x10^–5M_☉/yr, substantially lower than derived from optical or radio observations under assumptions of homogeneity. Additionally including the effects of line-blanketing, the wind performance factor, Mv_∞/(L_*/c), is reduced to ∼2.5. Hydrogen is severely depleted, but present at 9% by mass. Observations of the [CaIV] 3.21µm, [SiV] 10.51µm, and [NeIII] 15.56µm fine structure lines, from which we measure a terminal wind velocity of ∼950km/s, allow us to place constraints on the surface abundances of these elements. In all cases we find good agreement with cosmic abundances (adjusted to a hydrogen-poor environment) and thus with evolutionary predictions for WN stars.