Isochrones and luminosity functions for old white dwarfs

Using a new grid of models of cooling white dwarfs, we calculate isochrones and luminosity functions in the Johnson-Kron/Cousins and Hubble Space Tele scope (HST) filter sets for systems containing old white dwarfs. These new models incorporate a nongray atmosphere that is necessary to properly descr ibe the effects of molecular opacity at the cool temperatures of old white dwarfs. The various functions calculated and extensively tabulated and plot ted are meant to be as utilitarian as possible for observers, so all result s are listed in quantities that observers will obtain. The tables and plots developed should eventually prove critical in interpreting the results of HST's Advanced Camera observations of the oldest white dwarfs in nearby glo bular clusters, in understanding the results of searches for old white dwar fs in the Galactic halo, and in determining ages for star clusters using wh ite dwarfs. As a practical application we demonstrate the use of these resu lts by deriving the white dwarf cooling age of the old Galactic cluster M67 .