Identification of Cool White Dwarfs in the Noao Deep Wide-Field Survey

The chronology of star formation is recorded in the white dwarf luminosity function (WDLF). White dwarf (WD) structure implies a relatively simple connection between WD luminosity and age. First attempts to exploit WDs as chronometers [3,4,6] showed that the WDLF was a map of the history of star formation in the disk, and a significant shortfall of low-luminosity degenerates-the inevitable consequence of the finite age of the disk. The shortfall near log(L/L ⊙)≈-4.5 implies a disk age of 6.5–9.5 Gyr [2]. The WDLF from wide common proper motion binaries [5] does not show the shortfall seen by Liebert et at. (1988). This suggests that the disk is at least ∼10.5 Gyr old. Both Liebert et al. (1988) and Oswalt et al. (1996) WDLFs were derived from proper motion catalogs, hence may be affected by significant kinematical bias as well as incompleteness. The simple fact is, the faintest, age-dependent end of the WDLF is not yet reliably determined.