Wolf-Rayet stars (often referred to as WR stars) are a heterogeneous set of stars with unusual spectra showing prominent broad emission lines of highly ionised helium and nitrogen or carbon.
The spectra indicate very high surface temperatures of 30,000-200,000 Kelvin, surface enhancement of heavy elements, and strong stellar winds. Classic (or Population I) Wolf-Rayet stars are evolved, massive stars that have completely lost their outer hydrogen and are fusing helium or heavier elements in the core.
They are all highly luminous due to their high temperatures, thousands to millions of times the bolometric luminosity of the Sun, although not exceptionally bright visually since most of their radiation output is in the ultraviolet.
A significant proportion of WR stars are surrounded by nebulosity associated directly with the star, not just the normal background nebulosity associated with any massive star forming region, and not a planetary nebula formed by a post-AGB star. About 500 Wolf-Rayets are catalogued in our own Milky Way Galaxy.
They are rare, distant, and often obscured, and even today many aspects of their lives are unclear.
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There are no habitables planets possible at Wolf-Rayet Stars.