THE COOL WHITE-DWARF LUMINOSITY FUNCTION AND THE AGE OF THE GALACTIC DISK

We present new optical and infrared data for the cool white dwarfs in the proper motion sample of Liebert, Dahn, & Monet. Stellar properties -surface chemical composition, effective temperature, radius, surface gravity, mass, and luminosity-are determined from these data by using the model atmospheres of Bergeron, Saumon, & Wesemael. The space densi ty contribution is calculated for each star and the luminosity functio n (LF) for cool white dwarfs is determined. Comparing the LF to the mo st recent cooling sequences by Wood implies that the age of the local region of the Galactic disk is 8 +/- 1.5 Gyr. This result is consisten t with the younger ages now being derived for the globular clusters an d the universe itself.