Effects of mass loss on the evolution of massive stars. II. Critical mass loss rates

A critical mass-loss rate is discussed which, in the absence of binary mass transfer or extremely high mass-loss rates in the red-giant stage, determines whether a star will become a stripped core resembling a Wolf-Rayet star. Stars losing mass at this rate undergo two stages of 14N enhancement, and result in models resembling first WN and later WC stars. The nucleosynthetic yield of a star undergoing mass loss is affected. The 14N yield and C/O ratio are increased, and deltaHe/deltaZ is increased from 0.3 to as much as 3.0