A Wolf–Rayet nebula is a

nebula A nebula ('cloud' or 'fog' in Latin; pl. nebulae, nebulæ or nebulas) is a distinct luminescent part of interstellar medium, which can consist of ionized, neutral or molecular hydrogen and also cosmic dust. Nebulae are often star-forming regio ...

which surrounds a

Wolf–Rayet star Wolf–Rayet stars, often abbreviated as WR stars, are a rare heterogeneous set of stars with unusual spectra showing prominent broad emission lines of ionised helium and highly ionised nitrogen or carbon. The spectra indicate very high surface ...

. WR nebulae have been classified in various ways. One of the earliest was by the nature and origin of the nebula: *

HII region An H II region or HII region is a region of interstellar atomic hydrogen that is ionized. It is typically in a molecular cloud of partially ionized gas in which star formation has recently taken place, with a size ranging from one to hundre ...

s * ejecta-type nebulae * wind-blown bubbles This classification requires detailed study of each nebula and more recent attempts have been made to allow quick classification of nebulae based purely on their appearance. WR nebulae frequently are ring-shaped in appearance, possibly spherical. Others are irregular, either disrupted shells or formed from clumpy ejection. Examples of this type of nebula include

NGC 6888 The Crescent Nebula (also known as NGC 6888, Caldwell 27, Sharpless 105) is an emission nebula in the constellation Cygnus, about 5000 light-years away from Earth. It was discovered by William Herschel in 1792. It is formed by the fast stellar ...

NGC 2359 NGC 2359 (also known as Thor's Helmet) is an emission nebulaSEDS: NGC 2359
in the constellation

, and NGC 3199. Some WR nebulae have a prominent spiral structure, for example the

WR 104 WR 104 is a triple star system located about from Earth. The primary star is a Wolf–Rayet star (abbreviated as WR), which has a B0.5 main sequence star in close orbit and another more distant fainter companion. The WR star is surr ...

, formerly securing them with the categorization of pinwheel nebulae.

References

Nebulae {{nebula-stub