THE STRUCTURE OF PRE-TRANSITIONAL PROTOPLANETARY DISKS. II. AZIMUTHAL ASYMMETRIES, DIFFERENT RADIAL DISTRIBUTIONS OF LARGE AND SMALL DUST GRAINS IN PDS 70^,

Abstract

The formation scenario of a gapped disk, i.e., transitional disk, and its\nasymmetry is still under debate. Proposed scenarios such as disk-planet\ninteraction, photoevaporation, grain growth, anticyclonic vortex, eccentricity,\nand their combinations would result in different radial distributions of the\ngas and the small (sub-$\\mu$m size) and large (millimeter size) dust grains as\nwell as asymmetric structures in a disk. Optical/near-infrared (NIR) imaging\nobservations and (sub-)millimeter interferometry can trace small and large dust\ngrains, respectively; therefore multi-wavelength observations could help\nelucidate the origin of complicated structures of a disk. Here we report SMA\nobservations of the dust continuum at 1.3~mm and $^{12}$CO~$J=2\\rightarrow1$\nline emission of the pre-transitional protoplanetary disk around the solar-mass\nstar PDS~70. PDS~70, a weak-lined T Tauri star, exhibits a gap in the scattered\nlight from its disk with a radius of $\\sim$65~AU at NIR wavelengths. However,\nwe found a larger gap in the disk with a radius of $\\sim$80~AU at 1.3~mm.\nEmission from all three disk components (the gas and the small and large dust\ngrains) in images exhibits a deficit in brightness in the central region of the\ndisk, in particular, the dust-disk in small and large dust grains has\nasymmetric brightness. The contrast ratio of the flux density in the dust\ncontinuum between the peak position to the opposite side of the disk reaches\n1.4. We suggest the asymmetries and different gap-radii of the disk around\nPDS~70 are potentially formed by several (unseen) accreting planets inducing\ndust filtration.\n