The evolution of massive stars. I - The influence of mass loss on Population 1 stars

Abstract

We have studied the evolution of 15, 30, and 40 M/sub sun/ models with Y = 0.28 and Z = 0.02. All models have been evolved through core helium burning up to the point of carbon ignition. All models were evolved with and without the inclusion of mass loss. We have used a moderate mass loss rate with different efficiency factors for main-sequence and blue supergiant stars. Our results indicate that all massive stars ignite helium as blue supergiants. Stars with M/sub i/< or approx. =30 M/sub sun/ evolve redward very slowly and spend less than 1% of their total lifetimes as red supergiants. Above 30 M/sub sun/, the rate of redward evolution increases dramatically. Our 40 M/sub sun/ models spend up to 50% of their core helium-burning lifetimes as red supergiants. The primary effect of mass loss is to increase the rate of redward evolution during helium burning for all masses. The effects of mass loss on the internal structure, lifetimes, and surface abundances of the models are also discussed.