T Tauri Disk Evolution
          Caer-Eve McCabe, JPL/Caltech
          Andrea Ghez, UCLA
          Lisa Prato, Lowell Observatory
          Gaspard Duchene, Observatoire de Grenoble

          A high spatial resolution, 10-20 micron, survey of 65 T Tauri binary stars has been carried out at the Keck telescope. Combined with resolved near-infrared photometry and spectroscopic accretion diagnostics, we find that ten percent of stars with a mid-infrared excess do not appear to be accreting. In contrast to an actively accreting disk system, these 'passive disks' have significantly lower K-L colors that are, in most cases, consistent with photospheric emission, suggesting the presence of an inner disk hole. In addition, the presence of a passive disk appears to be dependent on the spectral type of the central star, with all passive disks occuring around M type stars.  The presence of a companion does not appear to be related to the presence of an inner disk hole; the binary systems with passive disks cover the entire range of separations present in the sample and a similar fraction of passive disks is observed in a sample of single stars. The mass dependence makes it unlikely that these systems are caused by the presence of a nearby, as yet unresolved, companion, leading us to suggest that we are seeing the effects of disk evolution.  The observed properties of the passive disks are consistent with models of inside-out disk evolution and suggest that the timescale for inner disk clearing is dependent on the mass of the central star, with disks around higher mass stars evolving faster than those around M type stars.