Winds of Wolf−Rayet stars: phenomenology of mass loss

Abstract

Population I Wolf–Rayet (WR) stars are the evolved descendants of massive (M ≥ 25M) O-type stars. The dense, fast radiatively-drivenWR winds efficiently hide all vital information about basic characteristics of the stellar cores. Observing binary systems with WR components, we put firm limits on the sizes and luminosities ofWR stars. In attempt to understand dynamics of the outflows, we study the micro-structure of WR winds, finding that they are composed from numerous dense clumps. The growing evidence that WR stars may be linked (collapsars) to the long Gamma Ray Bursters raises a question about rotation rates of WR stars. First results based on the observations of globally-structured winds of some WR stars show that they may be considered as moderately fast rotators. There is one more fascinating feature of the WR mass loss: some carbon-reach WR stars may form dust, thus placing them among the first prodigious dust-producers in the early Universe. Though we are yet to find how dust is formed in the extremely hostile environment of WR winds, we have made substantial progress over the past decade. Recent high spatial resolution near/mid-infrared imaging at the HST, Keck and Gemini, combined with abundant optical/UV spectroscopy and photometry, allows to map rapidly changing environments of the dust-forming regions and derive some basic properties of the freshly formed dust.