Wolf-Rayet stars are evolved, hot, massive stars, that exhibit very dusty strong stellar winds. Aperture Masking Interferometry observations of a number of nearby Wolf-Rayet stars recently found that all of the objects surveyed were binary stars, and that the dust production was occurring at the interaction (the shock front) of the stellar winds from the two stars in the binary (and not in free space above stellar surface as had been previously hypothesized). The dust is blown away from the stars by the stellar wind, and as the binary system rotates a rotating spiral of dust is formed (called a Pinwheel Nebula ). This dust formation process only occurs in a particular type of binary, and thus Wolf-Rayet (binary) stars are rare. The surface composition is usually mainly helium based with characteristic broad emission lines of carbon, nitrogen or oxygen. They usually have thermal radio emitters from free-free emission but could be also have nonthermal radio emitters. From this nonthermal radio emission it is possible to determine the luminosity, spectrum, time dependence, spatial distribution and polarization.
They were discovered spectroscopically in 1867 by French astronomers Charles Wolf and Georges Rayet, and the nature of Wolf-Rayet stars was determined by Peter George Tuthill , John D. Monnier and William C. Danchi using observations taken at the Keck Telescope in 1998.
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