The Effect of Environment on Massive Star Formation

In this contribution we review our recent numerical work discussing the essential role of the local cluster environment in assembling massive stars. First we show that massive stars are formed from low mass pre-stellar cores and become massive due to accretion. Proto-stars that benefit from this accretion are those situated at the center of a cluster's potential well, which is the focal point of the contraction of the cluster gas. Given that most of the mass which makes up a massive star in this model comes from the cluster environment rather than the core, it is important to model the molecular cloud environment accurately. Preliminary results of a simulation which accurately treats the chemistry and time-depenent thermodynamics of a molecular cloud show quantitatively similar star formation to previous models, but allow a true comparison to be made between simulation and observations. This method can also be applied to cases with varying metallicities allowing star formation in primordial gas to be studied. In general, these numerical studies of clustered star formation yield initial mass functions which are compatible with the Salpeter mass function. The only possible exception to this is in low density unbound regions of molecular clouds which lack very low and high mass stars.