Deep HST Imaging in 47 Tuc and NGC 6397: White Dwarfs and Brown Dwarfs in the Cluster and Field of NGC 6397

We report analysis of second epoch imaging of the very deep 126 orbit ACS integration in NGC 6397, yielding the deepest proper-motion selected color-magnitude diagram of a globular cluster. We reach past the faint end of the white dwarf cooling sequence and confirm the "blue hook" caused by H2 collision-induced absorption opacity. We also confirm a suspected population of faint red proper-motion members of NGC6397, many of which lie both fainter and redder than the theoretical limit for the hydrogen burning. Other proper motion members of NGC 6397 (with unusual colors) may be white dwarf/red dwarf binaries. Our reduced proper motion plot for the field reveals (for the first time) an extended white dwarf cooling sequence in the thick disk population, along with a well populated sequence of extremely faint red stars, many of which are also fainter and redder than the theoretical hydrogen burning limit. Supported by AURA STScI GO-11633 (R. M. Rich, PI)