Testing multi-mass dynamical models of star clusters with real data:
  mass segregation in three Galactic globular clusters
  We present the results of the analysis of deep photometric data for a sample
of three Galactic globular clusters (NGC5466, NGC6218 and NGC6981) with the aim
of estimating their degree of mass segregation and testing the predictions of
analytic dynamical models. The adopted dataset, composed by both Hubble Space
Telescope and ground based data, reaches the low-mass end of the mass functions
of these clusters from the center up to their tidal radii allowing to derive
their radial distribution of stars with different masses. All the analysed
clusters show evidence of mass segregation with the most massive stars more
concentrated than low-mass ones. The structures of NGC5466 and NGC6981 are well
reproduced by multimass dynamical models adopting a lowered-Maxwellian
distribution function and the prescription for mass segregation given by Gunn &
Griffin (1979). Instead, NGC6218 appears to be more mass segregated than model
predictions. By applying the same technique to mock observations derived from
snapshots selected from suitable N-body simulations we show that the deviation
from the behaviour predicted by these models depends on the particular stage of
dynamical evolution regardless of initial conditions.
