SCYON Abstract

Received on January 10 2001

The Impact of Tides on Cluster Formation

Authors	Christian M. Boily, Christophe Pichon
Affiliation	¹Astronomisches Rechen-Institut, Heidelberg D-69120, Germany, ²Observatoire de Strasbourg, 11 rue de l'Université, 67000 Strasbourg, France
Accepted by	Star2000 - Dynamics of Star Clusters and the Milky Way, ASP Conference Series, eds. S. Deiters et al.,
Contact	cmb@ari.uni-heidelberg.de
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Abstract

The homogeneity of metal abundances in clusters suggests that the epoch of star formation must have been short in order to avoid strong gradients in the stellar population, suggesting systems with little velocity dispersion at formation. When spherical clusters undergo violent relaxation a good fraction of stars describe nearly radial orbits. This situation likely gives rise to triaxial instability. Aspherical collapse also results in triaxial equilibria. However a net torque may now be exerted on individual clusters by the host galaxy's tide during radial infall, and induce streaming motion or rotation.

We investigate analytically the collapse of uniform-density spheroids to which we apply model galactic tides. We find that sub-virial clusters non-rotating at birth may yet show appreciable rotation in equilibrium.