DEPOSITION OF MASS, MOMENTUM, AND ENERGY BY MASSIVE STARS INTO THE INTERSTELLAR-MEDIUM

Models for the integrated output of mass, momentum, and energy from a population of massive stars are presented. We computed an extensive grid of radiatively wind models for hot stars and derived scaling relations for the mass-loss rates and wind velocities as a function of stellar parameters, including the metal abundance. It is found that the mass-loss rate scales with metal abundance like M is-proportional-to Z0.8. These wind models are combined with empirical stellar-wind data of other stellar types to obtain predictions for mass-loss rates and wind velocities in the entire upper Hertzsprung-Russell diagram. Theoretical and observational uncertainties are discussed. We synthesize integrated wind properties of massive stars in different chemical environments using evolutionary models by Maeder. The output of mass, momentum, and energy from stellar winds is computed for typical starburst parameters. In addition, the corresponding quantities resulting from supernova explosions are obtained. We evaluate the relative importance of winds and supernovae and find that in general winds are more important at higher metal content (Z greater-than-or-equal-to Z.) and during earlier phases of the burst (T less-than-or-equal-to 1 x 10(7) yr). The influence of the shape and mass cutoff of the initial mass function on wind and supernova properties is also discussed. We apply our models to a sample of luminous starburst galaxies with massive superwinds observed by Heckman et al. It is confirmed that stellar winds and supernova explosions can energize the superwinds if the kinetic energy of the stellar winds and supernova explosions is efficiently thermalized in the galaxian interstellar medium. We demonstrate that supernovae are not always the main contributors to the energy, momentum, and in particular the mass returned to the interstellar medium. The importance of stellar winds has been neglected in previous models of galactic superwinds.