Open clusters are collections of stars with similar ages and compositions, and as such provide a vital observational foundation for much of stellar astrophysics and stellar dynamics. The key for entry into these astrophysical laboratories is knowledge of the cluster membership, for stars in front of or behind a cluster appear to be within it. Since all stars gravitationally bound to a cluster move with very similar speed and direction, the path to identifying the members of a cluster is to measure the velocities for all stars visible within the cluster boundaries through proper motion and radial velocity determinations. This project is carrying out an exceptionally comprehensive and reliable census of the stellar and binary star populations in five rich old open clusters. The interface between stellar evolution and stellar dynamics is being explored through complete descriptions of the cluster mass functions, binary frequencies, and binary orbital elements as a function of radius, permitting detailed comparisons with n-body numerical simulations that include both dynamical and stellar evolution. The complex interplay between radiative and hydrodynamical processes within stellar cores is being explored through detailing the morphologies of main-sequence turnoff points.
Broader Impacts: This project is enhancing the research and teaching skills of future scientists by integrating graduate student dissertations, undergraduate theses, and research experiences for other undergraduate students. This work is associated with the NSF Center for the Integration of Research, Teaching, and Learning at the University of Wisconsin. A trilateral Taiwan-Baltic collaboration assists in the training and education of students in recently disadvantaged countries.