The Wolf-Rayet stars or W stars are very blue and very hot. Their spectra display wide emission lines. About 25% of them are spectroscopic binaries and some are eclipsing binaries. They are enormously concentrated toward the galactic equator. Forty percent are within one degree of the equator, 70% within two degrees, and 95% within 5 degrees. Wolf-Rayet stars are highly luminous and very short-lived. They are of great value (potentially) in locating and tracing the spiral-arm pattern of our galaxy, since they do not have time to move far from the spiral arm where they originate. Several of these stars have been discovered as the central exciting star in planetary nebulae.

The Wolf-Rayet stars seem to comprise two separate spectral sequences, carbon and nitrogen stars, whose special characteristics indicate different chemical compositions. It has not been decided just where these stars fit into the Hertzsprung-Russel diagram. Their high temperatures and high luminosities indicate that they should come before the O's, while their tenuous atmospheric shells or envelopes suggest a relationship with the giant M's or the symbiotic objects.

Copyright (c) 1997-99 Michael Erlewine