Stellar luminosity functions of rich star clusters in the Large Magellanic Cloud

We show the results of deep V and I HST photometry of G rich star clusters in the Large Magellanic Cloud with different ages and metallicities. The number of stars with measured magnitudes in each cluster varies from about 3000 to 10000 stars. We build stellar density and surface brightness profiles for the clusters and extract half-light radii and other structural parameters for each. We also obtain luminosity functions, Phi (M-V), down to M-V similar or equal to 6 (M/M. greater than or similar to 0.9), and investigate their dependence with distance from the cluster centre well beyond their half-light radius. In all clusters we find a systematic increase in the luminosity functions slope; Delta log Phi (M-V)/Delta (M-V), with radial distance from the centre. Among the clusters displaying significant mass segregation are the 2 youngest in the sample: NGC 1805, NGC 1818. For these two clusters we obtain present day mass functions. The NGC 1818 mass function is in excellent agreement with that derived by other authors, also using HST data. The young cluster mass function slopes differ, that of NGC 1805 being systematically steeper than NGC 1818. Since these are very young stellar systems (tau less than or similar to 40 Myrs), these variations may reflect the initial conditions rather than evolution due to internal dynamics.