A 0.4-20 mu m spectroscopic study of the clumped wind of WR 147

Abstract

We present a detailed spectroscopic study of the WN8(h)+B0.5 V binary system WR 147 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 =~ 4.1 mag at R_V =~ 2.7 are confirmed here. The distance to WR 147 is revised slightly upwards to 650 pc, 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 18 mu m 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^-5 M_sun yr^-1, substantially lower than derived from optical or radio observations under assumptions of homogeneity. Additionally including the effects of line-blanketing, the wind performance factor, spose Mv_infty /(L_*/c), is reduced to ~ 2.5. Hydrogen is severely depleted, but present at 9% by mass. Observations of the [Ca iv] 3.21 mu m, [S iv] 10.51 mu m, and [Ne iii] 15.56 mu m fine structure lines, from which we measure a terminal wind velocity of ~ 950 km s^-1, 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. Based on observations made with: ISO, a project of ESA with the participation of ISAS and NASA; the ISO-SWS, a joint project of SRON and MPE with contributions from KU-Leuven, Steward Observatory, and Phillips Laboratory; the Isaac Newton Telescope, which is operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchados of the Instituto de Astrofisica de Canarias; and the United Kingdom Infrared Telescope (UKIRT), operated on Mauna Kea, Hawaii, by the Joint Astronomy Centre and Royal Observatory Edinburgh.