SCYON Abstract

Received on December 9 2008

Quantitative analysis of clumps in the tidal tails of star clusters

AuthorsA. Just (1), P. Berczik (1,2), M.I. Petrov (3,2), and A. Ernst (1,4)
Affiliation(1) Astronomisches Rechen-Institut, Zentr. Astron. Univ. Heidelberg, Mönchhofstr. 12-14, 69120 Heidelberg
(2) Main Astronomical Observatory, National Academy of Sciences of Ukraine, 27 Akademia Zabolotnoho St. 03680 Kyiv, Ukraine
(3) Institut für Astronomie der Univ. Wien, Türkenschanzstr. 17, A-1180 Wien, Austria
(4) Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
Accepted byMonthly Notices of the Royal Astronomical Society


Tidal tails of star clusters are not homogeneous but show well defined clumps in observations as well as in numerical simulations. Recently an epicyclic theory for the formation of these clumps was presented. A quantitative analysis was still missing. We present a quantitative derivation of the angular momentum and energy distribution of escaping stars from a star cluster in the tidal field of the Milky Way and derive the connection to the position and width of the clumps. For the numerical realization we use star-by-star N-body simulations. We find a very good agreement of theory and models. We show that the radial offset of the tidal arms scales with the tidal radius, which is a function of cluster mass and the rotation curve at the cluster orbit. The mean radial offset is 2.77 times the tidal radius in the outer disc. Near the Galactic centre the circumstances are more complicated, but to lowest order the theory still applies. We have also measured the Jacobi energy distribution of bound stars and showed that there is a large fraction of stars (about 35%) above the critical Jacobi energy at all times, which can potentially leave the cluster. This is a hint that the mass loss is dominated by a self-regulating process of increasing Jacobi energy due to the weakening of the potential well of the star cluster, which is induced by the mass loss itself.