Published online by Cambridge University Press: 14 August 2015
The chemical abundances of hydrogen, helium, carbon, nitrogen, and oxygen in the winds of W-R stars bears directly on the problem of their evolutionary stage. The commonly held view that W-R stars are highly evolved objects has been based upon the apparent deficiencies of H in their envelopes and the enhanced strengths of CNO lines in the two sequences WN and WC (e.g. Gamow 1943). The picture that emerges is one in which many W-R stars are in the helium burning phase with the WC types more evolved than the WN stars. for this reason it is important to estimate the H content of as many WR stars as possible.