EFFECT OF MASS-LOSS AND OVERSHOOTING ON THE WIDTH OF THE MAIN-SEQUENCE OF MASSIVE STARS

The width of the main sequence of massive stars is investigated by using a composite n1 = n2 = 3 polytropic model with a composition discontinuity between the core and envelope to represent massive stars. The general properties of composite n1 = n2 = n polytropes are first discussed. Numerical integrations for n = 3 give the ratio of the radii at end and beginning of the main sequence which, together with the change in luminosity, determines the width of the main sequence. Mass loss and overshooting are taken into account within the context of the model. The model with a step discontinuity is then generalized to include a zone of variable mean molecular weight, and the effects of mass loss and overshooting are illustrated. The results of evolutionary calculations with mass loss and overshooting are discussed and compared with the results of composite polytropic models.