Kinematic signatures of tidal field in globular clusters

Filippo Contenta, Department of Physics, University of Surrey
Advisors: Anna-Lisa Varri, Douglas Heggie

Abstract: We present a large set of N-body simulations to study the evolution of tidally per- turbed clusters. In our survey, we explored the effects of the tidal field on the dynamical evolution of star clusters by varying the number of stars, the orbital properties, the galactic potential and the initial concentration of the models. Since the astrometric mission GAIA will soon allow us to explore the phase space of several Galactic globular clusters, we focused our analysis on the study of the kinematical properties of the models, especially in their outer parts. In particular, by studying the time evolution of the mean velocity vector, the velocity dispersion ten- sor, and the anisotropy parameter, we confirmed the existence of a significant degree of tangential anisotropy and of a moderate rotation in the outer parts of the clusters. We also started to explore the extent to which these properties could be explained in terms of the behaviour of the population of potential escapers and by other aspects of the dynamical evolution of the systems. In addition, we found an unexpected instability in star clusters with a King profile W0 = 5.0 and in Roche filling conditions. Such instability seems to be caused by a substantial and rapid expansion of the core of the cluster, associated with the escape of the neutron stars, as a result of the presence of an initial kick velocity of these stars.

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