Wolf-Rayet Stars

Wolf-Rayet Stars 

a class of stars characterized by very high temperatures and luminosities. They are distinguished from other stars by the presence of wide emission bands of hydrogen, helium, oxygen, carbon, and nitrogen in their spectra. This class of stars was named after the French astronomers C. Wolf and G. Rayet, who were the first to note the peculiarities in their spectra (1867). About 130 Wolf-Rayet stars are known in our galaxy; their average luminosity is 4,000 times that of the sun. More than 50 Wolf-Rayet stars have been found in the Magellanic clouds, the closest stellar systems to our galaxy. Their luminosity is equal to or slightly greater than that of similar stars of our galaxy. In the Milky Way, Wolf-Rayet stars are found mostly in regions of the spiral arms and are often linked with gas and dust clouds and clusters of normal hot stars. The effective temperature of Wolf-Rayet stars exceeds 50,000° C. Their radii are 10 to 15 times the radius of the sun, and their masses are on the order of 10 times the mass of the sun. Many Wolf-Rayet stars are close binary stars. The companion usually belongs to the normal hot stars of spectral class O. The width of the emission bands in the spectra of Wolf-Rayet stars reaches 50-100 angstroms. It is caused possibly by the radial expansion of the spherically symmetrical envelope formed as a result of the constant ejection of matter from the surfaces of Wolf-Rayet stars. Another hypothesis explains the diffusion of the lines by electron shells expanding in all directions. It is quite possible that the large-scale turbulence of matter plays a significant role in the atmosphere of WolfRayet stars. It is also possible that the expulsion of matter from the surface can occur as a result of rotation instability. This instability is increased by the presence of a massive companion.

REFERENCES

Vorontsov-Vel’iaminov, B. A. Gazovye tumannosti i novye zvezdy. Moscow-Leningrad, 1948.
Zvezdnye atmosfery. Moscow, 1963. (Translated from English.)

V. P. ARKHIPOVA