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Published online by Cambridge University Press: 19 July 2016
Firstly, a brief account is given on the recent progresses in model assumptions, which influence the evolution of surface abundances in massive stars. A concise overview of this chemical evolution is presented.
We discuss in detail the surface chemistry of WN and WC stars, in particular, the effects of the initial metallicity Z and mass loss rates on the resulting abundances. The abundances in WN stars are not very sensitive to model assumptions and are mainly a test on nuclear cross sections. Conversely, the chemical abundances in WC stars are very much model dependent. Major differences in the composition of WC stars (and subtype distributions) are expected according to their initial metallicity. The various models proposed to explain the N/C enrichments in blue supergiants and the properties of the progenitor of SN 1987A are reviewed.