(type of star with broad emission bands)
A Wolf-Rayet star (WR star) is a type of star that is
very hot, with strong, broad helium emission lines.
The broadening is presumed due to Doppler broadening of
lines emitted from a high velocity stellar wind.
Their spectrum indicates they are extremely hot,
30,000-200,000 K, and they are very luminous, at 10,000 to millions
of times the Sun's bolometric luminosity,
though most of the luminosity
is in ultraviolet and X-rays.
Some such stars are CSPNe and others are presumed
to be in a late evolutionary stage of very massive stars,
initially above 20 solar masses.
More than 200 Wolf-Rayet stars have been identified within the
Milky Way, the first having been noticed in 1867 in
the constellation Cygnus. Being so bright, individual
Wolf-Rayet stars have been identified in other galaxies,
e.g., throughout the Local Group,
and in distant galaxies, their characteristic spectrum is sometimes
prominent, and the galaxy is referred to as a Wolf-Rayet galaxy.
Some subtypes based on spectral features:
- carbon-rich Wolf-Rayet (WC) carbon line(s)s.
- nitrogen-rich Wolf-Rayet (WN) nitrogen line(s).
- late-type nitrogen-rich Wolf-Rayet (WNL) hydrogen line(s).
- early-type nitrogen-rich Wolf-Rayet (WNE) no hydrogen line(s).
- oxygen-rich Wolf-Rayet (WO) oxygen line(s).
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