The White Dwarf Distance to the Globular Cluster 47 Tucanae and its Age
Zoccali, M.; Bragaglia, A.; Rich, R. M.; Wesemael, F.; Holberg, J. B.; Carretta, E.; Marconi, G.; Ferraro, F. R.; Ortolani, S.; Renzini, A.; Gilmozzi, R.; Bohlin, R.
Germany, Italy, United States, Chile, Canada
Abstract
We present a new determination of the distance (and age) of the Galactic globular cluster 47 Tucanae (NGC 104) based on the fit of its white dwarf (WD) cooling sequence with the empirical fiducial sequence of local WD with known trigonometric parallax, following the method described by Renzini and collaborators. Both the cluster and the local WDs were imaged with HST WFPC2 using the same instrument setup. We obtain an apparent distance modulus of (m-M)V=13.27+/-0.14, consistent with previous ground-based determinations and shorter than that found using Hipparcos subdwarfs. Coupling our distance determination with a new measure of the apparent magnitude of the main-sequence turnoff based on our HST data, we derive an age of 13+/-2.5 Gyr. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.