NUMERICAL EXPERIMENTS SIMULATING THE DYNAMICS OF OPEN CLUSTERS IN THEGALACTIC FIELD

The velocity and spatial distributions of stars for a number of numeri cal dynamical open cluster models are studied, The initial structural and dynamical parameters of these cluster models are in agreement with observational data. The model open clusters are taken to be moving in circular orbits in the Galactic plane. During the dynamical evolution of an initially spherically-symmetric cluster, a core extended perpen dicular to the Galactic plane and a halo extended in the Galactic plan e form. Shells with enhanced stellar number densities also form; these are symmetrical relative to the cluster center and the Galactic plane . These shells are located at distances from 2-3 to 7-8 pc from the Ga lactic plane. The velocity distributions of the model cluster stars ar e extended perpendicular to the Galactic plane and along the direction of motion of the cluster in the Galaxy. The tidal radii for the clust er models are a factor of 1.5-2.0 smaller for stars with ''prograde'' motion than for those with ''retrograde'' motion. In the models consid ered, the ratio of the number of stars with prograde and retrograde mo tions remained virtually unchanged during the cluster evolution. There can be significant variations in the shape of the Kapeteyn diagram an d the corresponding diagram for residual stellar velocities in the pre sence of small variations in the initial stellar phase coordinates. Th is indicates that the stellar velocity distribution is unstable to sma ll initial phase coordinate perturbations. This instability is most no ticeable in the central regions of the model clusters. There are also significant variations of the shape of these diagrams and of the stell ar velocity distributions on time intervals of the order of 0.8-1.0 mi llion years, Parameters are determined for the spatial distributions o f the stellar number densities, velocities, and velocity dispersions a veraged over the oscillation period of the uniform cluster field and p rojected onto three coordinate planes. The gravitational potentials of the cluster models are also found. There are sometimes significant va riations of these parameters for small variations of the initial stell ar phase coordinates, The deeper the stars are placed below the cluste r tidal surface at the initial time, the greater the instability of th e cluster model parameters averaged over the oscillation period of the uniform field with respect to small variations in the initial phase c oordinates. The construction of open cluster models in terms of veloci ties and coordinates averaged over the oscillation period of the unifo rm field is discussed in detail.