High‐Resolution Submillimeter Constraints on Circumstellar Disk Structure

We present a high spatial resolution submillimeter continuum survey of 24circumstellar disks in the Tau-Aur and Oph-Sco star formation regions using theSMA. In the context of a simple model, we use broadband SEDs and submillimetervisibilities to derive constraints on some basic parameters that describe thestructure of these disks. For the typical disk in the sample we infer a radialsurface density distribution \Sigma ~ r^-p with a median p ~ 0.5, althoughconsideration of the systematic effects of some of our assumptions suggest thatsteeper distributions with p ~ 0.7-1.0 are more reasonable. The distribution ofthe outer radii of these disks shows a distinct peak at R_d = 200 AU, with onlya few cases where the disk emission is completely unresolved. Based on thesedisk structure measurements, the mass accretion rates, and the typical spectraland spatial distributions of submillimeter emission, we show that theobservations are in good agreement with similarity solutions for steadyaccretion disks that have a viscosity parameter alpha ~ 0.01. We provide newestimates of the spectral dependence of the disk opacity with a median spectralindex of ~0.7, corrected for optically thick emission. This typical value isconsistent with model predictions for the collisional growth of solids tomillimeter size scales in the outer disk. Although direct constraints on planetformation in these disks are not currently available, the extrapolated densitydistributions inferred here are substantially shallower than those calculatedbased on the solar system or extrasolar planets and typically used in planetformation models. It is possible that we are substantially underestimating diskdensities due to an incomplete submillimeter opacity prescription.Comment: submitted to ApJ (8/22/06