Young star clusters in the Large Magellanic Cloud: NGC 1805 and NGC 1818

Abstract

We present colour-magnitude diagrams for two rich (~10^4 Msun) Large Magellanic Cloud star clusters with ages ~10^7 years, constructed from optical and near-infrared data obtained with the Hubble Space Telescope. These data are part of an HST project to study LMC clusters with a range of ages. In this paper we investigate the massive star content of the young clusters, and determine the cluster ages and metallicities, paying particular attention to Be star and blue straggler populations and evidence of age spreads. We compare our data to detailed stellar population simulations to investigate the turn-off structure of ~25 Myr stellar systems, highlighting the complexity of the blue straggler phenomenon.

15 pages, accepted for publication in MNRAS, postscript version with higher quality figures available from http://www.ast.cam.ac.uk/~raj/biblio.html

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