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

Abstract

We show the results of deep V and I HST photometry of 6 rich star clusters in the Large Magellanic Cloud with di erent ages and metallicities. The number of stars with measured magnitudes in each cluster varies from about 3000 to 10 000 stars. We build stellar density and surface brightness pro les for the clusters and extract half-light radii and other structural parameters for each. We also obtain luminosity functions, Φ(MV ), down to MV- ~ 6 (M/Mʘ >~ 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, ∆logΦ(MV )/∆(MV ), with radial distance from the centre. Among the clusters displaying signi cant 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 di er, that of NGC 1805 being systematically steeper than NGC 1818. Since these are very young stellar systems (Τ <~τ 40 Myrs), these variations may reflect the initial conditions rather than evolution due to internal dynamics.