Investigations of Star Clusters. Star cluster research at Yerkes Observatory primarily involves astrometric (proper motions) and photometric studies of globular clusters, dwarf spheroidal galaxies, and a few open clusters. Proper motions are used to derive cluster membership, study the internal dynamics of the nearer clusters, and derive space velocities. High quality photometry is normally obtained along with the astrometry to produce very clean color-magnitude diagrams. In some globular clusters the proper motions are combined with radial velocities obtained by Dr. Cudworth and others to further constrain dynamical models and to derive distances with sufficient precision to provide a useful new calibration of the globular cluster distance scale independent of "standard candle" assumptions. Absolute proper motions and hence space velocities are being determined for globulars and some dwarf spheroidal galaxies. With an emphasis on space velocity derivations for very distant globulars and dwarf speroidals, Dr. Cudworth will be able to place better constrains on the mass of the Milky Way.
