A Wolf–Rayet star is a massive star of spectral type WO or WC that shows strong emission lines of highly ionised carbon, oxygen and nitrogen. They are extremely hot and luminous, with surface temperatures in the range 30,000-200,000 K and luminosities up to several million times that of the Sun. The name “Wolf–Rayet” (abbreviated WR) comes from the two French astronomers Charles Wolf and Georges Rayet who first identified this class of stars in 1867.
WR stars are thought to be evolved stars that have lost most or all of their hydrogen envelope through stellar winds. The high temperature and luminosity cause them to have very high mass-loss rates; as a result they are losing mass at a rate of about 10^−5 solar masses per year – much higher than for any other known type of star. This means that WR stars are relatively short-lived compared to other types of star; the most massive ones live for only a few million years before ending their lives in supernova explosions.
The spectra of WR stars show very broad emission lines resulting from their high rotation speeds; some also show narrower absorption lines due to their binary nature. Their spectrum can be used to determine their surface temperature, luminosity and rotational velocity. By studying these properties we can learn about the evolutionary history of these fascinating objects.