About the stage of evolution of Wolf-Rayet stars

The basis for the suggestion by Bhatia and Underhill (1988) to the effect that Wolf-Rayet stars are young massive objects only now arriving on the main sequence and still enveloped in a remnant of their natal cloud is reviewed, and it is shown that the arguments of Lamers et al. (1991) that Wolf-Rayet stars are the endpoints of massive star evolution are not valid. The hypothesis that Population I Wolf-Rayet stars are massive young stellar objects associated with O and B stars is useful for coordinating the available information about Wolf-Rayet stars. A few central stars of planetary nebulae also show a Wolf-Rayet-type spectrum; they appear to be low-mass stars at a late stage of evolution. It is argued that exhibiting a Wolf-Rayet-type spectrum is a trait of a few massive stars and of a few evolved low-mass stars.