or nitrogen, or sometimes oxygen. Once included as type O stars, the Wolf–Rayet stars of class W or WR are notable for spectra lacking hydrogen lines...

Robert investigated the wind clumps observed in the spectrum of the Cygnus Wolf-Rayet stars, using the Canada-France-Hawaii Telescope with her advisor Anthony...

supergiants will evolve back to blue supergiants, Luminous blue variables, or Wolf-Rayet stars before their cores collapse, and Mu Cephei appears to be massive...