THE MASSES OF TRANSITION CIRCUMSTELLAR DISKS: OBSERVATIONAL SUPPORT FOR PHOTOEVAPORATION MODELS

We report deep Submillimeter Array observations of 26 pre-main-sequence (PMS) stars with evolved inner disks. These observations measure the mass of the outer disk (r similar to 20-100 AU) across every stage of the dissipation of the inner disk (r < AU) as determined by the IR spectral energy distributions (SEDs). We find that only targets with high mid-IR excesses are detected and have disk masses in the 1-5 M(Jup) range, while most of our objects remain undetected to sensitivity levels of M(DISK) similar to 0.2-1.5 M(Jup). To put these results in a more general context, we collected publicly available data to construct the optical to millimeter wavelength SEDs of over 120 additional PMS stars. We find that the near-IR and mid-IR emissions remain optically thick in objects whose disk masses span 2 orders of magnitude (similar to 0.5-50 M(Jup)). Taken together, these results imply that, in general, inner disks start to dissipate only after the outer disk has been significantly depleted of mass. This provides strong support for photoevaporation being one of the dominant processes driving disk evolution.