Wolf-Rayet star
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Wolf-Rayet stars (often referred to as WR stars) are evolved, hot, massive stars which have very strong stellar winds. Wolf-Rayet stars are a normal stage in the evolution of massive stars, in which strong, broad emission lines of helium and nitrogen ("WN" sequence) or helium, carbon, and oxygen ("WC" sequence) are visible.
Due to their strong emission lines they are relatively easy to identify in nearby galaxies. About 150 Wolf-Rayets are known in our own Milky Way Galaxy, about 100 are known in the Large Magellanic Cloud, while only 12 have been identified in the Small Magellanic Cloud. Wolf-Rayet stars were discovered spectroscopically in 1867 by the French astronomers Charles Wolf and Georges Rayet using visual spectrometery at Paris Observatory.
A recent campaign to image several Wolf-Rayet binaries at high resolution has found many specimens which are surrounded by pinwheel nebulae, with dust created by the interaction of winds in a close binary system.
Furthermore some (roughly 10% of the galactic) central stars of planetary nebulae are - despite their lower masses - also of the WR-type, i.e. they show emission line spectra with broad lines from helium, carbon and oxygen.
The best known (and most visible) example of a Wolf-Rayet star is Gamma Velorum (γ Vel), which is a bright star visible to those located south of 40 degrees northern latitude. One of the members of the star system (Gamma Velorum is actually four stars) is a Wolf-Rayet star. Due to the exotic nature of its spectrum (bright emission lines in lieu of dark absorption lines) it is dubbed "the spectral gem of the southern sky".
See also
External links
- [1] Some Wolf-Rayet stars in binaries are close enough that we can image a rotating "pinwheel nebula" showing the dust generated by colliding winds in the binary system, from Aperture Masking Interferometry observations.
- [2]Wolf-Rayet Stars: Spectral Classifications
- [3]ApJ 525:L97-L100 Nov. 10, 1999. Monnier, Tuthill & Danchi: Pinwheel Nebula Around WR98a (PDF)
- [4]ApJ Jan. 3,2005. Dougherty, et. al.: High Resolution Radio Observations of the Colliding Wing Binary WR140 (PDF)
- [5]A catalog of northern Wolf-Rayet Stars and the Central Stars of Planetary Nebulae (Harvard)ca:Estrella de Wolf-Rayet
cs:Wolf-Rayetova hvězda de:Wolf-Rayet-Stern es:Estrella de Wolf-Rayet fr:Étoile Wolf-Rayet it:Stella di Wolf-Rayet nl:Wolf-Rayetster ja:ウォルフ・ライエ星 pl:Gwiazda Wolfa-Rayeta sk:Wolf-Rayetova hviezda fi:Wolfin–Rayetin tähti sv:Wolf-Rayet-stjärna