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Astron. Astrophys. 337, 363-371 (1998)

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On the dissolution of evolving star clusters

Simon F. Portegies Zwart * 1, 2, Piet Hut 3, Junichiro Makino 2 and Stephen L.W. McMillan 4

1 Astronomical Institute Anton Pannekoek , Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
2 Department of Information Science and Graphics, College of Arts and Science, University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153, Japan
3 Institute for Advanced Study, Princeton, NJ 08540, USA
4 Department of Physics and Atmospheric Science, Drexel University, Philadelphia, PA 19104, USA

Received 13 March 1998 / Accepted 25 May 1998


Using direct N-body simulations which include both the evolution of single stars and the tidal field of the parent galaxy, we study the dynamical evolution of globular clusters and rich open clusters. We compare our results with other N-body simulations and Fokker-Planck calculations. Our simulations, performed on the GRAPE-4, employ up to 32,768 stars. The results are not in agreement with Fokker-Planck models, in the sense that the lifetimes of stellar systems derived using the latter are an order of magnitude smaller than those obtained in our simulations. For our standard run, Fokker-Plank calculations obtained a lifetime of 0.28 Gyr, while our equivalent N-body calculations find [FORMULA] Gyr. The principal reason for the discrepancy is that a basic assumption of the Fokker-Plank approach is not valid for typical cluster parameters. The stellar evolution timescale is comparable to the dynamical timescale, and therefore the assumption of dynamical equilibrium leads to an overestimate of the dynamical effects of mass loss. Our results suggest that the region in parameter space for which Fokker-Planck studies of globular cluster evolution, including the effects of both stellar evolution and the galactic tidal field, are valid is limited. The discrepancy is largest for clusters with short lifetimes.

Key words: methods: numerical – celestial mechanics, stellar dynamics – stars: evolution – globular clusters: general – open clusters and associations: general

* Japan Society for the Promotion of Science Fellow

Send offprint requests to: Simon Portegies Zwart, (spz@grape.c.u-tokyo.ac.jp)

© European Southern Observatory (ESO) 1998

Online publication: August 17, 1998