Proper motion with HST: Searching for high-velocity stars in the core of the globular cluster 47 Tucanae

摘要

Binary stars play an essential role during the late phases of the dynamical evolution of a globular cluster. Hard binaries are known to exist in cluster cores, e.g., in the form of millisecond pulsars (about half of the millisecond pulsars observed in 47 Tucanae are such hard binaries). We are using WFPC2 to obtain deep U (F300W) images of the core of 47 Tuc at three different epochs over two years, with which we will measure differential proper motions to a 1-(sigma) limit of 0.23 mas/yr. By using the F300W filter we can measure stars over the whole color-magnitude diagram, from the red-giant branch to well down the main sequence. We report on the first-epoch (Cycle 5) observations of this project. Although no proper motions are available yet, some preliminary by-product results are presented. These include luminosity functions and color-magnitude diagrams for the core of 47 Tuc and the light curves of variable blue straggler stars and of a candidate X-ray source. 32 refs., 5 figs.