Cool White Dwarfs : Cooling Theory and Galactic Implications

The understanding of the physics of cool white dwarfs (WD) bears important consequences for Galactic evolution and cosmological implications. The observed cutoff in the disk WD luminosity function (WDLF) yields the determination of the age of the Galactic disk, as suggested initially by Winget et al. (1987). The recent microlensing observations toward the LMC (Alcock et al., 1996) suggest that WDs might provide a substantial fraction of the halo dark matter (Chabrier, Segretain & Méra, 1996; Adams & Laughlin, 1996). The correct analysis of these applications implies a correct WD cooling theory and reliable photometric predictions, which in turn require accurate interior and atmosphere models. Important improvement in this latter domain has been accomplished recently by Bergeron, Saumon & Wesemael (1995) and Bergeron, Wesemael & Beauchamp (1995), which yields the determination of photometric color indices and bolometric corrections down to 4000 K (see Leggett, these proceedings). In this paper, we review the most recent improvement in WD interior and cooling theory.