Astrophotography by Anthony Ayiomamitis

Wolf-Rayet Nebula Image Gallery

Although only 227 Wolf-Rayet stars have been identified to-date, they are a delight to both observers and photographers, for they produce stunning bubble nebulae around luminous and massive stars nearing the end of their evolutionary cycle. First noted by French astronomers Charles Wolf and Georges Rayet in the mid 1860's, these stars are characterized with unorthodox spectra with broad emission lines strong in ionized helium, carbon, oxygen and nitrogen (these stars are further subdivided into WN and WC stars depending on a stronger nitrogen or carbon emission line respectively).

These very luminous stars are also very short-lived. During the normal phase of their life cycle, the interstellar medium disperses stellar material, thus forming an interstellar bubble. When the star has then finally reached the end of its life cycle, a strong stellar wind now helps in the rapid depletion of stellar mass and which accumulates in the form of an (emission) nebula residing into the previously formed interstellar bubble with the WR star behind this sequence of events being often quite visible (particularly in photos).

Wolf-Rayet stars are characterized with cores whose mass is only 10 to 20 solar masses and temperatures which vary between 25,000 and 60,000 degrees Kelvin. The Seventh Catalogue of Galactic Wolf-Rayet Stars boasts a short but complete list of 227 entries as of 2001. Approximately 100 of these stars are found in the Large Magellenic Cloud; they rarely occur in clusters and there is a suspicion that they may be precursors to supernovas. These bubble clouds can span large portions of the sky (20-30 arc minutes); they can have a high surface brightness; and many are within easy reach of modest amateur telescopes.

More recently, studies have uncovered approximately 50 planetary nebulae to possess central stars which have characteristic Wolf-Rayet spectra. For further details, see Pena et al here, Medina et al here and especially Gorny et al here.

Note: For two excellent articles, the interested reader is referred to Astronomy Magazine (Feb/2006: 68-71, Jul/2008: 34-39) as well as the online article here. For a list of the twenty brightest Wolf-Rayet stars, click here. An alternate online list of the complete catalog is available here and here. Finally, for a list of Wolf-Rayet stars visible from the northern hemisphere, click here and/or here.

Wolf-Rayet Nebulae

WR 155 in Cas

WR 128 in Sge

WR 133 in Cyg

Crescent Nebula
WR 136 in Cyg

WR 153 in Cep

Bubble Nebula
BD+602522 in Cas

Campbell's Hydrogen Star
BD+303639 in Cyg