White Dwarfs in the SuperCOSMOS Sky Survey: the Thin Disk, Thick Disk
  and Spheroid Luminosity Functions
  We present a magnitude and proper motion limited catalogue of ~10,000 white
dwarf candidates, obtained from the SuperCOSMOS Sky Survey by means of reduced
proper motion selection. This catalogue extends to magnitudes r~19.75 and
proper motions as low as mu ~0.05"/yr, and covers nearly three quarters of the
sky. Photometric parallaxes provide distance estimates accurate to ~50%. This
catalogue is used to measure the luminosity functions for disk and spheroid
white dwarfs, using strict velocity cuts to isolate subsamples belonging to
each population. Disk luminosity functions measured in this manner are really a
conglomerate of thin and thick disk objects, due to the significant velocity
overlap between these populations. We introduce a new statistical approach to
the stellar luminosity function for nearby objects that succesfully untangles
the contributions from the different kinematic populations, without the need
for stringent velocity cuts. This improves the statistical power by allowing
all stars to contribute to the luminosity function, even at tangential
velocities where the populations are indistinguishable. This method is
particularly suited to white dwarfs, for which population discrimination by
chemical tagging is not possible. We use this technique to obtain the first
measurement of the thick disk white dwarf luminosity function, while also
improving constraint on both the thin disk and spheroid luminosity functions.
We find that the thin disk, thick disk and spheroid populations contribute to
the local white dwarf density in roughly 79%/16%/5% proportions.
