Mass spectra of young stars

In an effort to understand the factors that determine the initial mass function of stars, the available data on the mass spectra of young stars in different regions have been studied for possible correlations with the properties of the associated molecular clouds and the spatial distributions of the stars. There appear to be differences in the stellar mass spectra in different regions: for example in Taurus, where the molecular gas is relatively dispersed and the stars are in scattered small groups, the stars are predominantly of low mass, whereas in Orion, where the gas is in massive condensed clouds and the stars are mostly in a single large cluster, the mass spectrum is relatively depleted in low-mass stars. The most massive stars appear to form in the dense cores of forming clusters or associations, and the mass of the most massive young star increases systematically with the mass of the associated molecular cloud. The data are consistent with a picture in which molecular cloud cores grow by accretion and become progressively more massive and condensed, while forming stars in larger and more condensed clusters and with a mass spectrum that increasingly favours massive stars. In this picture the more massive stars form by accumulation processes, rather than by fragmentation, in the dense core regions of protoclusters. Stellar winds may play an important role in limiting the masses that forming stars can attain; if so, the maximum stellar mass should increase with the density of the ambient gas and with the amount of turbulence present, a prediction that is in agreement with observations.