PROTOPLANETARY DISK STRUCTURES IN OPHIUCHUS

Abstract

We present the results of a high angular resolution (0 3 ≈ 40 AU) Submillimeter Array survey of the 345 GHz (870 μm) thermal continuum emission from nine of the brightest, and therefore most massive, circumstellar disks in the ∼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, Σ ∝ ( R / R c ) −γ exp [ − ( R / R c ) 2−γ ], the best-fit models for the sample disks have characteristic radii R c ≈ 20–200 AU, high disk masses M d ≈ 0.005–0.14 M ☉ (a sample selection bias), and a narrow range of radial Σ gradients (γ ≈ 0.4–1.0) around a median γ = 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 α ≈ 0.0005–0.08. Three of the sample disks show large ( R ≈ 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.