The HST/ACS Survey of Galactic Globular Clusters

We present an overview and the first results of a large ACS survey of Galactic globular clusters. This Hubble Space Telescope (HST) Treasury project is designed to obtain photometry with S/N ≳ 10 for main sequence stars with masses ≳ 0.2M_⊙ in a sample of globulars using the Advanced Camera for Surveys (ACS) Wide Field Channel. Our sample consists primarily of globular clusters within about 20 kpc of the Sun with fairly low reddening. We also added a few clusters of special interest toward the Galactic bulge as well as six clusters believed to be members of the Sagittarius dwarf spheroidal galaxy. This sample of 66 globular clusters was observed with HST using 134 orbits. We plan to explore a wide variety of scientific issues with these data including the formation timescale of the Milky Way halo, the age of the Universe, the dynamical evolution of stars in globular clusters (e.g. mass segregation), and the mass of the Milky Way and its gravitational potential field.