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Astron. Astrophys. 319, 839-849 (1997)


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Rotating globular clusters

III. Evolutionary survey

Pierre-Yves Longaretti 1 and Christophe Lagoute 2

1 Laboratoire d'Astrophysique de l'Observatoire de Grenoble, B.P. 53, F-38041 Grenoble Cedex 9, France
2 Observatoire Midi-Pyrénées, 14 avenue E. Belin, F-31400 Toulouse, France

Received 13 May 1996 / Accepted 27 August 1996

Abstract

We describe a simple model which allows us to investigate the effects of rotation on the evolution of globular clusters and of their flattening. The model relies on a generalization to rotating clusters of sequences of quasi-equilibrium models known as King sequences, which are able to follow the evolution of globular clusters prior to core collapse. Our model includes in a simplified way the effects of internal relaxation, tidal heating by passage through the Galactic disk, and stellar evolution. We investigate a broad range of initial conditions in the cluster mass, Galactocentric distance, initial mass function power-law index, initial concentration, and initial rotation energy. We also report the results of a similar study of the Large Magellanic Cloud clusters. The major findings of this investigation are the following: i) the combined effects of rotation, tidal shocking and stellar evolution is to reduce the domain of survival of rotating clusters to higher concentrations with respect to nonrotating ones; ii) rotating clusters reach core collapse at lower concentrations than their nonrotating counterparts; iii) the three modelled processes are likely to be responsible for the luminosity/flattening and relaxation timescale/flattening correlations reported in the literature; iv) the larger flattening of the Magellanic globular clusters is mostly the result of their large spread in age, as reported by Frenk and Fall (1982), and, to a lesser extent, of the smaller efficiency of the evolution in the Magellanic Cloud tidal environment with respect to the Galaxy, assuming similar initial conditions.

Key words: celestial mechanics, stellar dynamics – globular clusters – galaxies: star clusters – Magellanic Clouds

Send offprint requests to: P.Y. Longaretti

© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998

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