Abstract details

The stellar initial mass function (IMF) has been constrained to a reasonable degree of accuracy. While different populations do show some different forms of the IMF, the overall distribution of shapes is surprisingly uniform and can be well represented by a power-law with the Salpeter/Massey index above about 0.5 Msun, while being flatter at lower masses. The physical mass-range of stars is limited empirically to less than about 150 Msun, apparently independently of metallicity. Differences in the shape of the IMF seen in various populations can mostly be attributed to unresolved binaries and dynamical evolution of the host system. There is therefore no evidence at all of possible systematic changes of the IMF with physical star-forming conditions, which would, however, be expected from theoretical work. This uniformity of the IMF simplifies the modelling of stellar populations, but at the same time it constitutes a challenge for star-formation theory.