A member of a class of rare, exceptionally hot stars with surface temperatures of 20,000-50,000 K. Their spectra show strong broad-band emission lines: in WC stars, carbon dominates, whereas in WN stars the dominant emission lines are of nitrogen. It is believed that there is a genuine difference in composition between the two subgroups. The emission lines are thought to originate in a rapidly expanding envelope through which the star is losing mass. Some are the central stars of planetary nebulae, but their evolutionary status is not fully understood. The name comes from two nineteenth-century French astronomers, Charles Wolf and Georges Rayet.