Dynamical evolution of star clusters in tidal fields

• DOI: 10.1046/j.1365-8711.2003.06286.x
• Publication Date: 2003-05-13T09:05:57Z
• Authors: H. Baumgardt; J. Makino
• Keywords: methods : N-body simulations; Monte-Carlo Simulations; Black-Hole; Ccd Photometry; Astrophysics (astro-ph); M-Circle-Dot; FOS: Physical sciences; Main-Sequence; N-Body Simulations; Astrophysics; 01 natural sciences; 520; Initial Mass Function; Galactic Globular-Clusters; Unequal Masses; 0103 physical sciences; globular clusters : general; stellar dynamics; Stellar Evolution

22 pages, 26 figures,accepted for publication in MNRAS<br/>We report results of a large set of N-body calculations aimed to study the evolution of multi-mass star clusters in external tidal fields. Our clusters start with the same initial mass-functions, but varying particle numbers, orbital types and density profiles. Our main focus is to study how the stellar mass-function and other cluster parameters change under the combined influence of stellar evolution, two-body relaxation and the external tidal field. We find that the lifetimes of star clusters moving on similar orbits scale as T sim T_RH^x, where T_RH is the relaxation time, and the exponent x depends on the initial concentration of the cluster and is around x approx 0.75. From the results for the lifetimes, we predict that between 53% to 67% of all galactic globular clusters will be destroyed within the next Hubble time. Low-mass stars are preferentially lost and the depletion is strong enough to turn initially increasing mass-functions into mass-functions which decrease towards the low-mass end. The details of this depletion are insensitive to the starting condition of the cluster. The preferential depletion of low-mass stars from star clusters leads to a decrease of their mass-to-light ratios except for a short period close to final dissolution. The fraction of compact remnants is increasing throughout the evolution and they are more strongly concentrated towards the cluster cores than main-sequence stars. For a sample of galactic globular clusters with well observed parameters, we find a correlation between the observed slope of the mass-function and the lifetimes predicted by us. It seems possible that galactic globular clusters started with a mass-function similar to what one observes for the average mass-function of the galactic disc and bulge. (Abridged)<br/>