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.,|
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.