A survey for cool white dwarfs and the age of the Galactic disc

We describe a new multicolour proper motion survey for cool white dwarfs (C WDs). The observational data base consists of similar to 300 digitally scan ned Schmidt plates in ESO/SERC held 287. The entire survey procedure, from the raw Schmidt plate data to the final white dwarf luminosity function (WD LF), is described, with special emphasis on completeness concerns. We obtai n a sample of 58 WDs, for which we have follow-up CCD photometry and spectr oscopy of a representative subsample. Effective temperatures and luminositi es of our sample objects are determined by comparing photometry with the mo del atmosphere predictions of Bergeron, Saumon & Wesemael. Space densities are calculated using an adaptation of Schmidt's (1/V-max) method, from whic h a WDLF is constructed. Comparison of our observational LF with the models of both Wood and Garcia-Berro et al. indicates an age for the local Galati c disc of 10(+3)(-1) Gyr. Importantly, we find no evidence of incompletenes s in our survey sample. Proper motion number counts imply the survey is com plete, and the WD sample passes the (V/V-max) completeness test.