Catching a Milky Way open cluster in its last breath

Abstract

Theoretical models have suggested peculiar velocity dispersion profiles of star clusters facing dissolution. They predicted that, besides bound stars that still belong to the star cluster, and unbound ones already stripped off, there is an intermediate population of stars that having acquired the enough energy to escape the cluster are still within the cluster Jacobi radius. Both, potential escapers and unbound stars, show hot kinematics, not observed along tidal tails of star clusters. We report on the first evidence of an open cluster with stars crossing such a transitional scenario, namely: ASCC 92. The open cluster gathers nearly 10 per cent of its initial total mass, and is moving towards Galactic regions affected by higher interstellar absorption. Precisely, the obscured appearance of the cluster could have hampered disentangling its true internal dynamical evolutionary stage, previously.