| Abstract: | The kinematics of stars in open-cluster models are investigated. The central regions of these model clusters are fairly “cool,
” leading to gravitational instability in the cluster cores. A temporary virilization is observed in the model clusters, during
which an appreciable fraction of the fluctuation energy of the cluster is temporarily transformed into the kinetic energy
of the peculiar motions of stars. The duration of this stage can reach ∼108 yr. The origins of this temporary virialization of the model clusters are discussed. The instability of the intrinsic fluctuations
of the phase density in the centers of six clusters and model clusters is investigated. Several new regions of unstable phase-density
fluctuations are found, in addition to those already known. The observed and model clusters can move toward a stable equilibrium
state when the density of the cluster core both decreases and increases. The structure of regions of instability of the phase-density
fluctuations in the centers of the six clusters is studied. Resonance curves for the amplitudes of steady-state phase-density
fluctuations in the center of NGC 6705 are constructed. Analysis of the structure of the regions of instability indicates
an appreciable rate of fluctuation-energy loss due to relaxation effects. The instability increments and widths of regions
of instability fall off with increasing distance of the cluster from the Galactic center. An important role in the formation
of regions of instability may be played by resonances between the frequency of the orbital motion of the cluster in the Galaxy
and the frequencies of intrinsic phase-density fluctuations in the centers of the clusters considered. |
