Compact star clusters of the LMC H ii region N 11 C ?

Based on imaging and spectroscopy obtained at the ESO NTT telescope and using an efficient image analysis algorithm, we study the core of the LMC OB association LH 13, particularly the two compact stellar clusters Sk–66◦41 and HNT in the H ii region N 11C. We resolve Sk–66◦41 into 15 components and for the first time the HNT cluster into 70 stars, and derive photometry for the members. Moreover, from medium resolution spectroscopy we determine the spectral types for sixteen stars in N 11C. We compare the color-magnitude diagrams of the clusters with that of the field stars and discuss the cluster ages. With an age of ∼ 100 Myr, the HNT cluster appears significantly older than the very young (≤ 5 Myr) Sk–66◦41 starburst. We suggest that most of the ‘field’ O-stars in the core of N 11C have actually been ejected from Sk–66◦41 through dynamical interactions in the compact cluster. The properties of the Sk–66◦41 and HNT clusters suggest that we are viewing different star formation regions lying at different distances along the same line of sight.