PROTOPLANETARY DISK STRUCTURES IN OPHIUCHUS

We present the results of a high angular resolution (0 ''.3 approximate to 40 AU) Submillimeter Array survey of the 345 GHz (870 mu m) thermal continuum emission from nine of the brightest, and therefore most massive, circumstellar disks in the similar to 1 Myr-old Ophiuchus star-forming region. Using two-dimensional radiative transfer calculations, we simultaneously fit the observed continuum visibilities and broadband spectral energy distribution for each disk with a parametric structure model. Compared to previous millimeter studies, this survey includes significant upgrades in modeling, data quality, and angular resolution that provide improved constraints on key structure parameters, particularly those that characterize the spatial distribution of mass in the disks. In the context of a surface density profile motivated by similarity solutions for viscous accretion disks, Sigma proportional to (R/R-c)(-gamma) exp [-(R/R-c)(2-gamma)], the best-fit models for the sample disks have characteristic radii R-c approximate to 20-200 AU, high disk masses M-d approximate to 0.005-0.14 M-circle dot (a sample selection bias), and a narrow range of radial Sigma gradients (gamma approximate to 0.4-1.0) around a median gamma = 0.9. These density structures are used in conjunction with accretion rate estimates from the literature to help characterize the viscous evolution of the disk material. Using the standard prescription for disk viscosities, those combined constraints indicate that alpha approximate to 0.0005-0.08. Three of the sample disks show large (R approximate to 20-40 AU) central cavities in their continuum emission morphologies, marking extensive zones where dust has been physically removed and/or has significantly diminished opacities. Based on the current requirements of planet formation models, these emission cavities and the structure constraints for the sample as a whole suggest that these young disks may eventually produce planetary systems, and have perhaps already started.