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We used the deep colour-magnitude diagrams (CMDs) of five rich LMC clusters(NGC1805, 1818, 1831, 1868, and Hodge14) observed with HST/WFPC2 to derivetheir present day mass function (PDMF) and its variation with position withinthe cluster. The PDMF was parameterized as a power law in the availablemain-sequence mass range of each cluster, typically 0.9 <~ m/M_sun <~ 2.5; itsslope was determined at different positions spanning from the very centre outto several core radii. The CMDs in the central regions of the clusters werecarefully studied earlier, resulting in accurate age, metallicity, distancemodulus, and reddening values. The slope alpha (where Salpeter is 2.35) wasdetermined in annuli by following two distinct methods: 1) a power law fit tothe PDMF obtained from the systemic luminosity function (LF); 2) a statisticalcomparison between observed and model CMDs. In all clusters, significant masssegregation is found from the positional dependence of the PDMF slope: alpha <~1.8 for R <= 1.0 R_core and alpha ~ Salpeter inside R=2~3 R_core (except forHodge 14, where alpha ~ Salpeter for R ~ 4 R_core). The results are robust inthe sense that they hold true for both methods used. The CMD method revealsthat unresolved binaries flatten the PDMF obtained form the systemic LF, butthis effect is smaller than the uncertainties in the alpha determination. Foreach cluster we estimated dynamical ages inside the core and for the entiresystem. In both cases we found a trend in the sense that older clusters haveflatter PDMF, consistent with a dynamical mass segregation and stellarevaporation.Comment: 11 pages, 11 Postscript figures, Astronomy & Astrophysics, accepted  10 January 200

Mass segregation in rich LMC clusters from modelling of deep HST colour–magnitude diagrams