Wolf–Rayet star

Wolf–Rayet star (WR star) A type of very luminous star, believed to be a late stage in the evolution of stars born with spectral type O which have lost their hydrogen envelopes through strong stellar winds, exposing the helium core. Wolf–-Rayet stars are of over 10 solar masses and have surface temperatures of 20 000–-40 000 K. They have strong stellar winds with mass–loss rates of order 10⁵ solar masses per year, and outflow velocities of 2000–-3000 km/s. Their spectra show strong emission lines, and they are classified as WN or WC types according to whether nitrogen or carbon dominates. They may be the progenitors of supernovae of Types Ib and Ic, and of some *gamma-ray bursters. They are named after the French astronomers Charles Joseph Étienne Wolf (1827–1918) and Georges Antoine Pons Rayet (1839–1906), who discovered them in 1867. The brightest example is 2nd-mag. Gamma Velorum.