Linking the rotation of a cluster to the spins of its stars: The
  kinematics of NGC6791 and NGC6819 in 3D
  The physics governing the formation of star clusters is still not entirely
understood. One open question concerns the amount of angular momentum that
newly formed clusters possess after emerging from their parent gas clouds.
Recent results suggest an alignment of stellar spins and binary orbital spins
in star clusters, which support a scenario in which clusters are born with net
angular momentum cascading down to stellar scales. In this paper, we combine
Gaia data and published line of sight velocities to explore if NGC6791 and
NGC6819, two of the clusters for which an alignment of stellar spins has been
reported, rotate in the same plane as their stars. We find evidence for
rotation in NGC6791 using both proper motions and line of sight velocities. Our
estimate of the inclination angle is broadly consistent with the mean
inclination that has been determined for its stars, but the uncertainties are
still substantial. Our results identify NGC6791 as a promising follow-up
candidate to investigate the link between cluster and stellar rotation. We find
no evidence for rotation in NGC6819.
