MILLIMETER OBSERVATIONS OF THE TRANSITION DISK AROUND HD 135344B (SAO 206462)

We present similar to 1 '' resolution 1.3 mm dust continuum and spectral line ((CO)-C-12 and (CO)-C-13 J = 2-1) observations of the transitional disk system HD 135344B obtained with the Submillimeter Array. The disk shows a Keplerian rotation pattern with an inclination of similar to 11 degrees, based on the spatially and spectrally resolved (CO)-C-12 and (CO)-C-13 emission. The data show clear evidence for both dust and gas surface density reductions in the inner region of the disk (radius less than or similar to 50 AU) from the continuum and (CO)-C-13 J = 2-1 data, respectively. The presence of this inner cavity in both the dust and gas is more consistent with clearing by giant planet formation than by photoevaporation or by grain growth. There is also an indication of global CO gas depletion in the disk, as the mass estimated from (CO)-C-13 emission (similar to 3.8 x 10(-4) M-circle dot) is about two orders of magnitude lower than that derived from the 1.3mm continuum (similar to 2.8 x 10(-2) M-circle dot).