Properties of Wolf-Rayet stars from X-ray to radio data

This review outlines the impact of observations across the spectrum (X-rays to radio) on our understanding of the basic physical, chemical, wind and mass loss properties of Wolf-Rayet stars. Optical spectropolarimetry indicates that similar to15% of the WR stars have anisotropic winds, whilst the majority have globally spherically symmetric outflows. All WR stars probably have winds structured (clumped) on the smaller scale as evidenced from: thermal radio spectral indices, optical-UV continuum/line/polarisation variablity and time-series spectroscopy, and the ubiquity of wind X-ray emission. ROSAT results indicate L-X(WR) = 10(31-33) ergs(-1) with kTsimilar or equal to0.3 keV. WR mass loss rates may be lower than previously thought: mean, clumping-corrected rates from radio data yield M(WN) similar or equal to 3 x 10(-5) M(circle dot)yr(-1) and M(WC)similar or equal to2 x 10(-5) M(circle dot)yr(-1). Analyses of UV-optical-IR spectra lead to good constraints on T-eff and L/L-circle dot and confirm the chemical separation of the WN and WC classes: WN stars show H-He-C-N abundances reflecting CNO-burning products, and WC(WO) stars show He-burning products. ISO data are confirming the H-deficiency of WC winds, and reveal a substantially enhanced Neon abundance in WC stars.