  Current X-ray missions are providing high-quality X-ray spectra from neutron
stars (NSs) in quiescent low-mass X-ray binaries (qLMXBs). This has motivated
us to calculate new hydrogen-atmosphere models, including opacity due to
free-free absorption and Thomson scattering, thermal electron conduction, and
self-irradiation by photons from the compact object. We have constructed a
self-consistent grid of neutron star models covering a wide range of surface
gravities as well as effective temperatures, which we make available to the
scientific community.
  We present multi-epoch Chandra X-ray observations of the qLMXB X7 in the
globular cluster 47 Tuc, which is remarkably nonvariable on timescales from
minutes to years. Its high-quality X-ray spectrum is adequately fit by our
hydrogen-atmosphere model without any hard power-law component or narrow
spectral features. If a mass of 1.4 Msol is assumed, our spectral fits require
that its radius be in the range R=14.5^{+1.8}_{-1.6} km (90% confidence),
larger than expected from currently preferred models of NS interiors. If its
radius is assumed to be 10 km, then a mass of M=2.20^{+0.03}_{-0.16} Msol is
required. Using models with the appropriate surface gravity for each value of
the mass and radius becomes important for interpretation of the highest quality
data.
