  We present a 0.5-2.2 micron scattered light spectrum of the circumstellar
disk around TW Hya from a combination of spatially resolved HST STIS
spectroscopy and NICMOS coronagraphic images of the disk. We investigate the
morphology of the disk at distances > 40 AU over this wide range of
wavelengths, and identify the presence of a depression in surface brightness at
~80 AU that could be caused by a gap in the disk. Additionally, we quantify the
surface brightness, azimuthal symmetry, and spectral character of the disk as a
function of radius. Our analysis shows that the scattering efficiency of the
dust is largely neutral to blue over the observed wavelengths. We model the
disk as a steady alpha-disk with an ad hoc gap structure. The thermal
properties of the disk are self-consistently calculated using a
three-dimensional radiative transfer code that uses ray-tracing to model the
heating of the disk interior and scattered light images. We find a good fit to
the data over a wide range of distances from the star if we use a model disk
with a partially filled gap of 30% depth at 80 AU and with a self-similar
truncation knee at 100 AU. The origin of the gap is unclear, but it could arise
from a transition in the nature of the disk's dust composition or the presence
of a planetary companion. Based on scalings to previous hydrodynamic
simulations of gap opening criteria for embedded proto-planets, we estimate
that a planetary companion forming the gap could have a mass between 6-28
M_Earth.
