What are Wolf-Rayet Stars?
Wolf-Rayet stars (sometimes abbreviated as WR stars) are old, very massive stars (~20 solar masses) in the process of ejecting their material into the interstellar medium. In contrast with the Sun, which ejects 10-14% of its mass per year through solar wind, Wolf-Rayet stars lose 10-5 of their mass per year. Their surfaces are extremely hot — 25,000 to 50,000 K. Wolf-Rayet stars have used up most of their nuclear fuel, being forced to fuse heavier elements such as helium and nitrogen (“WN” sequence) or helium, carbon, and oxygen (“WC” sequence). These heavy elements are kicked up around the atmosphere of the star, and they absorb the light and heat given off by the star, being propelled outwards. Wolf-Rayet stars have atmospheres so large that their thickness is comparable to the star itself. The large quantity of superheated material being ejected gives WR stars strong emissions spectra, so notable that Wolf-Rayets are among the easiest stars to observe in adjacent galaxies. 230 Wolf-
