The missing cavities in the SEEDS polarized scattered light images of transitional protoplanetary disks: a generic disk model

TL;DR

This paper introduces a generic disk model that explains the apparent absence of cavities in near-infrared scattered light images of transitional disks, reconciling observations across multiple wavelengths and suggesting dust filtration and grain growth processes.

Contribution

The paper presents a unified disk model that accounts for multi-wavelength observations of transitional disks, highlighting dust decoupling and differential dust distributions inside cavities.

Findings

Model reproduces observed scattered light and sub-mm images.

Decoupling of small and large dust grains inside cavities.

Increases in gas-to-dust ratio toward the inner disk.

Abstract

Transitional circumstellar disks around young stellar objects have a distinctive infrared deficit around 10 microns in their Spectral Energy Distributions (SED), recently measured by the Spitzer Infrared Spectrograph (IRS), suggesting dust depletion in the inner regions. These disks have been confirmed to have giant central cavities by imaging of the submillimeter (sub-mm) continuum emission using the Submillimeter Array (SMA). However, the polarized near-infrared scattered light images for most objects in a systematic IRS/SMA cross sample, obtained by HiCIAO on the Subaru telescope, show no evidence for the cavity, in clear contrast with SMA and Spitzer observations. Radiative transfer modeling indicates that many of these scattered light images are consistent with a smooth spatial distribution for micron-sized grains, with little discontinuity in the surface density of the micron-sized grains at the cavity edge. Here we present a generic disk model that can simultaneously account for the general features in IRS, SMA, and Subaru observations. Particularly, the scattered light images for this model are computed, which agree with the general trend seen in Subaru data. Decoupling between the spatial distributions of the micron-sized dust and mm-sized dust inside the cavity is suggested by the model, which, if confirmed, necessitates a mechanism, such as dust filtration, for differentiating the small and big dust in the cavity clearing process. Our model also suggests an inwardly increasing gas-to-dust-ratio in the inner disk, and different spatial distributions for the small dust inside and outside the cavity, echoing the predictions in grain coagulation and growth models.