Cluster kinematics and stellar rotation in NGC 419 with MUSE and adaptive optics

We present adaptive optics (AO)-assisted integral-field spectroscopy of the intermediate-age star cluster NGC 419 in the Small Magellanic Cloud. By investigating the cluster dynamics and the rotation properties of main-sequence turn-off (MSTO) stars, we demonstrate the power of AO-fed MUSE observations for this class of objects. Based on 1 049 radial velocity measurements, we determine a dynamical cluster mass of 1.4± 0.2× 10^5 M_⊙ and a dynamical mass-to-light ratio of 0.67 ± 0.08, marginally higher than simple stellar population predictions for a Kroupa initial mass function. A stacking analysis of spectra at both sides of the extended MSTO reveals significant rotational broadening. Our analysis further provides tentative evidence that red MSTO stars rotate faster than their blue counterparts. We find average Vsin i values of 87± 16 and 130± 22 {km s^{-1}} for blue and red MSTO stars, respectively. Potential systematic effects due to the low-spectral resolution of MUSE can reach 30 {km s^{-1}} but the difference in Vsin i between the populations is unlikely to be affected.