On the dissolution of star clusters in the Galactic centre. I. Circular
  orbits
  We present N-body simulations of dissolving star clusters close to galactic
centres. For this purpose, we developed a new N-body program called nbody6gc
based on Aarseth's series of N-body codes. We describe the algorithm in detail.
We report about the density wave phenomenon in the tidal arms which has been
recently explained by Kuepper et al. (2008). Standing waves develop in the
tidal arms. The wave knots or clumps develop at the position, where the
emerging tidal arm hits the potential wall of the effective potential and is
reflected. The escaping stars move through the wave knots further into the
tidal arms. We show the consistency of the positions of the wave knots with the
theory in Just et al. (2009). We also demonstrate a simple method to study the
properties of tidal arms. By solving many eigenvalue problems along the tidal
arms, we construct numerically a 1D coordinate system whose direction is always
along a principal axis of the local tensor of inertia. Along this coordinate
system, physical quantities can be evaluated. The half-mass or dissolution
times of our models are almost independent of the particle number which
indicates that two-body relaxation is not the dominant mechanism leading to the
dissolution. This may be a typical situation for many young star clusters. We
propose a classification scheme which sheds light on the dissolution mechanism.
