1996A&A...312..649W

In how far does the presence of both radial velocities and proper motions constrain the orbital structure and the dynamical distance of a spherical star cluster? To investigate this question, we create artificial stellar systems of various sizes and orbital structure, and use a Quadratic Programming technique for the modeling. This technique turns out to be a very fast and dependable method. We find that, if the observational errors are small (25% or less), 500 data points are no luxury in order to reach reliable conclusions. Larger errors will lead to an overestimation of the mass and will tend to isotropise the orbital structure. By comparing the line of sight velocity dispersions with the proper motion dispersions we find that an accuracy of 10-15% on the dynamical distance is obtainable for good quality data.