Open Cluster formation and dynamics

Theories of cluster formation range from the highly dynamic through to quasi-equilibrium and slow contraction scenarios. These different routes lead to different initial cluster structures and kinematics (Jackson & Jeffries, 2010, MNRAS, 407, 465, Tan et al., 2006, ApJ, 641, L121; Proszkow et al., 2009, ApJ, 697, 1020). Subsequent evolution depends on many factors, including the initial conditions, star formation efficiency and tidal interactions. Whilst hydrodynamic and N-body simulations are developing, a fundamental requirement is an extensive body of detailed observations. A complete comparison requires precise position and velocity phase-space information resolving the internal cluster kinematics (≤ 0.5 km/s) that can be provided by the spectroscopy of the Gaia-ESO survey (Jackson & Jeffries, 2010, MNRAS, 407, 465; Tan et al., 2006, ApJ, 641, L121; Proszkow et al., 2009, ApJ, 697, 1020). Even more sophisticated studies will follow combination of the results with Gaia astrometry. The velocity fields within the youngest clusters betray their formation history, whilst the kinematics of the older clusters and the age dependence of their mass functions test theories of cluster destruction.