Wolf-Rayet Star

Massive stars at an advanced stage of stellar evolution, losing mass at a very high rate (right). They have masses typically >25 Msun and brief lifetimes. About 220 are known in our own Galaxy out of an estimated 1,000-2,000 such objects; most are hidden by dust. Wolf-rayet stars have average temperatures >25,000 K and luminosities up to 106 Lsun. Powerful stellar winds driven by intense radiation pressure, eject ~10 Msun per million years at speeds up to 3,000 km/s. These speeds result in broad emission lines in the spectra.

Image source: http://upload.wikimedia.org/wikipedia/commons/b/be/Wolf_rayet2.jpg.

These stars probably descend from O stars that have lost their H envelopes, revealing a He core. They may be subclassified into 2 main types: WN stars dominated by He and N  and nitrogen emission lines, but containing some C, and  WC stars lacking N and dominated by He, C, and O emission lines. About 50% of Wolf-Rayet stars occur in binary systems; proposed companions include another Wolf-Rayet star, or a black hole or neutron star. The only confirmed Wolf-Rayet companions so identified are other massive stars. Wolf-Rayet stars probably end their lives as either Type Ib or Type Ic supernovae.

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