The white dwarf distance to the globular cluster NGC 6752 (and its age) with the Hubble Space Telescope

Deep Hubble Space Telescope (HST) observations with WFPC2 of the nearby globular cluster NGC 6752 have allowed us to obtain accurate photometry for the cluster white dwarfs (WDs). A sample of local WDs of known trigonometric parallax and mass close to that of the duster WDs have also been observed with WFPC2. Matching the duster and the local WD sequences provides a direct measure of the distance to the cluster: (m - M)(0) = 13.05, with an uncertainty less than +/-0.1 mag, which allows a substantial reduction in the uncertainty in the age of the cluster. Indeed, coupling this value of the duster distance to the cluster metallicity, helium abundance, and ly-element enhancement [alpha/Fe] = 0.5 yields an age of 15.5 and 14.5 Gyr using evolutionary models that do not include or do include helium diffusion, respectively. The uncertainty affecting these age determinations is similar to 10%. The majority of the cluster WDs appear to be of the DA variety, while the color-magnitude location of two WDs is consistent with the DB type. This suggests a duster DB/DA ratio similar to that of WDs in the solar neighborhood.