The effect of stellar winds on the formation of a protocluster
  We present SPH simulations of protoclusters including the effects of winds from massive stars. Using a particle-injection method, we investigate the effect of structure close to the wind sources and the short-timescale influence of winds on protoclusters. Structures such as disks and gaseous filaments have a strong collimating effect. By a different technique of injecting momentum from point sources, we compare the large-scale, long-term effects of isotropic and intrinsically-collimated winds and find them to be similar. Both types of wind dramatically slow the global star formation process, but the timescale on which they expel significant mass from the cluster is rather long (approaching 10 freefall times). Clusters may then experience rapid star formation early in their lifetimes, before switching to a mode where gas is gradually expelled, while star formation proceeds much more slowly. This complicates conclusions regarding slow star formation derived from measuring the star-formation efficiency per freefall time. Estimates of the efficacy of winds in dispersing clusters derived simply from the total wind momentum flux may not be very reliable. This is due to material being expelled from deep within stellar potential wells, often to velocities well in excess of the cluster escape velocity, and also to the loss of momentum flux through holes in the gas distribution. Winds have little effect on the accretion--driven stellar IMF except at the very high-mass end, where they serve to prevent some of the most massive objects accreting. We also find that the morphology of the gas, the rapid motions of the wind sources and the action of accretion flows prevent the formation of bubble-like structures. This may make it difficult to discern the influence of winds on very young clusters. 
J. E. Dale, I.A. Bonnell