  We report on the discovery of the extremely low-mass, hydrogen-rich white
dwarf, NLTT 11748. Based on measurements of the effective temperature
(8540+/-50 K) and surface gravity (log g = 6.20+/-0.15) obtained by fitting the
observed Balmer line profiles with synthetic spectra, we derive a mass of
0.167+/-0.005 M_solar. This object is one of only a handful of white dwarfs
with masses below 0.2 M_solar that are believed to be the product of close
binary evolution with an episode of Roche lobe overflow onto a degenerate
companion (neutron star or white dwarf). Assuming membership in the halo
population, as suggested by the kinematics and adopting a cooling age of 4.0 -
6.3 Gyrs for the white dwarf, we infer a progenitor mass of 0.87 - 0.93
M_solar. The likely companion has yet to be identified, but a search for radial
velocity variations may help constrain its nature.
