Ruprecht 147: a paradigm of dissolving star cluster

Abstract

We employed recent Gaia/DR2 data to investigate the dynamical status of the nearby (300 pc), old (2.5 Gyr) open cluster Ruprecht~147. We found prominent leading and trailing tails of stars along the cluster orbit, which demonstrates that Ruprecht~147 is losing stars at fast pace. Star counts indicate the cluster has a core radius of 33.3 arcmin, and a tidal radius of 137.5 arcmin. The cluster also possesses an extended corona, which cannot be reproduced by a simple King model. We computed the present-day cluster mass using its luminosity and mass function, and derived an estimate of 234$\pm$52 $M_{\odot }$. We also estimated the cluster original mass using available recipes extracted from N-body simulations obtaining a mass at birth of 50000$\pm$6500 $M_{\odot }$. Therefore dynamical mass loss, mostly caused by tidal interaction with the Milky Way, reduced the cluster mass by about 99\%. We then conclude that Ruprecht~147 is rapidly dissolving into the general Galactic disc.

13 pages, 10 figure, in press in the Astronomical Journal

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• On the Motion of Stars in the Pleiades according to Gaia DR2 Data
• Eclipsing binaries in the open cluster Ruprecht 147. III: The triple system EPIC 219552514 at the main-sequence turnoff
• The relation of the Alpha Persei star cluster with the nearby stellar stream
• Unresolved multiple stars and Galactic clusters' mass estimates
• First evidence of a collision between two unrelated open clusters in the Milky Way