  Mid-infrared spectrophotometric observations have revealed a small sub-class
of circumstellar disks with spectral energy distributions (SEDs) suggestive of
large inner gaps with low dust content. However, such data provide only an
indirect and model-dependent method of finding central holes. Imaging of
protoplanetry disks provides an independent check of SED modeling. We present
here the direct characterization of three 33-47 AU radii inner gaps, in the
disks around LkHa 330, SR 21N and HD 135344B, via 340 GHz (880 micron) dust
continuum aperture synthesis observations obtained with the Submillimeter Array
(SMA). The large gaps are fully resolved at ~0\farcs3 by the SMA observations
and mostly empty of dust, with less than 1 - 7.5 x 10^-6 Msolar of fine grained
solids inside the holes. Gas (as traced by atomic accretion markers and CO 4.7
micron rovibrational emission) is still present in the inner regions of all
three disks. For each, the inner hole exhibits a relatively steep rise in dust
emission to the outer disk, a feature more likely to originate from the
gravitational influence of a companion body than from a process expected to
show a more shallow gradient like grain growth. Importantly, the good agreement
of the spatially resolved data and spectrophotometry-based models lends
confidence to current interpretations of SEDs, wherein the significant dust
emission deficits arise from disks with inner gaps or holes. Further SED-based
searches can therefore be expected to yield numerous additional candidates that
can be examined at high spatial resolution.
