870 micron Imaging of a Transitional Disk in Upper Scorpius: Holdover
  from the Era of Giant Planet Formation?
  We present 880 micron images of the transition disk around the star [PZ99]
J160421.7-213028, a solar-mass star in the nearby Upper Scorpius association.
With a resolution down to 0.34 arcsec, we resolve the inner hole in this disk,
and via model fitting to the visibilities and spectral energy distribution we
determine both the structure of the outer region and the presence of sparse
dust within the cavity. The disk contains about 0.1 Jupiter masses of
mm-emitting grains, with an inner disk edge of about 70 AU. The inner cavity
contains a small amount of dust with a depleted surface density in a region
extending from about 20-70 AU. Taking into account prior observations
indicating little to no stellar accretion, the lack of a binary companion, and
the presence of dust near 0.1 AU, we determine that the most likely mechanism
for the formation of this inner hole is the presence of one or more giant
planets.
