With the Keck Interferometer, we have studied at 2 um the innermost regions
of several nearby, young, dust depleted "transitional" disks. Our observations
target five of the six clearest cases of transitional disks in the
Taurus/Auriga star-forming region (DM Tau, GM Aur, LkCa 15, UX Tau A, and RY
Tau) to explore the possibility that the depletion of optically thick dust from
the inner disks is caused by stellar companions rather than the more typical
planet-formation hypothesis. At the 99.7% confidence level, the observed
visibilities exclude binaries with flux ratios of at least 0.05 and separations
ranging from 2.5 to 30 mas (0.35 - 4 AU) over >= 94% of the area covered by our
measurements. All targets but DM Tau show near-infrared excess in their SED
higher than our companion flux ratio detection limits. While a companion has
previously been detected in the candidate transitional disk system CoKu Tau/4,
we can exclude similar mass companions as the typical origin for the clearing
of inner dust in transitional disks and of the near-infrared excess emission.
Unlike CoKu Tau/4, all our targets show some evidence of accretion. We find
that all but one of the targets are clearly spatially resolved, and UX Tau A is
marginally resolved. Our data is consistent with hot material on small scales
(0.1 AU) inside of and separated from the cooler outer disk, consistent with
the recent SED modeling. These observations support the notion that some
transitional disks have radial gaps in their optically thick material, which
could be an indication for planet formation in the habitable zone (~ a few AU)
of a protoplanetary disk.Comment: 36 pages, 7 figures. Accepted for publication in Ap