Accurate Masses for the Primary and Secondary in the Eclipsing White
  Dwarf Binary NLTT 11748
  We measure the radial velocity curve of the eclipsing detached white dwarf
binary NLTT 11748. The primary exhibits velocity variations with a
semi-amplitude of 273 km/s and an orbital period of 5.641 hr. We do not detect
any spectral features from the secondary star, or any spectral changes during
the secondary eclipse. We use our composite spectrum to constrain the
temperature and surface gravity of the primary to be Teff = 8690 (140) K and
log g = 6.54 (0.05), which correspond to a mass of 0.18 Msol. For an
inclination angle of 89.9 deg. derived from the eclipse modeling, the mass
function requires a 0.76 Msol companion. The merger time for the system is 7.2
Gyr. However, due to the extreme mass ratio of 0.24, the binary will most
likely create an AM CVn system instead of a merger.
