  We present sensitive, sub-arcsecond resolution Submillimeter Array
observations of the protoplanetary disk around the nearby, pre-main sequence
spectroscopic binary V4046 Sgr. We report for the first time a large inner hole
(r=29 AU) spatially resolved in the 1.3 mm continuum emission and study the
structure of this disk using radiative transfer calculations to model the
spectral energy distribution (SED), continuum visibilities, and spectral line
emission of CO and its main isotopologues. Our modeling scheme demonstrates
that the majority of the dust mass is distributed in a narrow ring (centered at
37 AU with a FWHM of 16 AU) that is ~5 times more compact than the gas disk.
This structure implies that the dust-to-gas mass ratio has a strong spatial
variation, ranging from a value much larger than typical of the interstellar
medium (ISM) at the ring to much smaller than that of the ISM at larger disk
radii. We suggest that these basic structural features are potentially
observational signatures of the accumulation of solids at a local gas pressure
maximum. These models also require a substantial population of ~micron-sized
grains inside the central disk cavity. We suggest that this structure is likely
the result of dynamical interactions with a low-mass companion, although
photoevaporation may also play a secondary role.
