The dynamics of NGC 1866

High-precision radial velocity measurements have been obtained for 62 stars in the young LMC cluster NGC 1866 using the Las Campanas 2.5m with échelle spectrograph. The mass-weighted mean-square velocity dispersion is σ 2 = 6.5 ± 1.3 km 2 s −2 . The mass of the cluster M( r < 20) = 8.1 ± 1.6 × 10 4 M ⊙ , implying a M/L of 0.20 ± 0.04 in solar units.