The Structure of Pre-transitional Protoplanetary Disks. II. Azimuthal Asymmetries, Different Radial Distributions of Large and Small Dust Grains in PDS~70

TL;DR

This study uses multi-wavelength observations to reveal azimuthal asymmetries and differing radial dust distributions in the PDS 70 protoplanetary disk, suggesting planet-induced dust filtration as a key formation process.

Contribution

It provides the first detailed comparison of small and large dust grain distributions and asymmetries in PDS 70 using SMA observations, highlighting potential planet-induced structures.

Findings

Larger gap (~80 AU) observed at 1.3 mm compared to NIR (~65 AU)

Asymmetric brightness in dust and gas components with a flux contrast ratio of 1.4

Evidence suggests unseen planets may cause dust filtration and asymmetries

Abstract

The formation scenario of a gapped disk, i.e., transitional disk, and its asymmetry is still under debate. Proposed scenarios such as disk-planet interaction, photoevaporation, grain growth, anticyclonic vortex, eccentricity, and their combinations would result in different radial distributions of the gas and the small (sub-$\mu$m size) and large (millimeter size) dust grains as well as asymmetric structures in a disk. Optical/near-infrared (NIR) imaging observations and (sub-)millimeter interferometry can trace small and large dust grains, respectively; therefore multi-wavelength observations could help elucidate the origin of complicated structures of a disk. Here we report SMA observations of the dust continuum at 1.3~mm and $^{12}$CO~$J=2\rightarrow1$ line emission of the pre-transitional protoplanetary disk around the solar-mass star PDS~70. PDS~70, a weak-lined T Tauri star, exhibits a gap in the scattered light from its disk with a radius of $\sim$65~AU at NIR wavelengths. However, we found a larger gap in the disk with a radius of $\sim$80~AU at 1.3~mm. Emission from all three disk components (the gas and the small and large dust grains) in images exhibits a deficit in brightness in the central region of the disk, in particular, the dust-disk in small and large dust grains has asymmetric brightness. The contrast ratio of the flux density in the dust continuum between the peak position to the opposite side of the disk reaches 1.4. We suggest the asymmetries and different gap-radii of the disk around PDS~70 are potentially formed by several (unseen) accreting planets inducing dust filtration.