  A detailed analysis of halo white dwarf candidates is presented, which is
based on model atmosphere fits to observed energy distributions built from
photoelectric or photographic magnitudes. Most of the candidates identified in
reduced proper motion diagrams are shown to be too warm (Teff > 5000 K) and
most likely too young to be members of the galactic halo, while the tangential
velocities of the cooler and thus older white dwarfs are shown to be entirely
consistent with the disk population. The results suggest that some white dwarf
stars born in the young disk may have high velocities with respect to the local
standard of rest. Such objects could represent the remnants of donor stars from
close mass-transfer binaries that produced type Ia supernovae via the single
degenerate channel, or other scenarios suggested in the literature. Ongoing
surveys that rely solely on reduced proper motion diagrams are likely to
identify more of these high velocity young degenerates, rather than to unveil
the old white dwarf population of the galactic halo. The importance of infrared
photometry for studying extremely cool white dwarfs is also emphasized.
