High-Contrast Near-Infrared Imaging Polarimetry of the Protoplanetary Disk around RY Tau

TL;DR

This study uses high-resolution near-infrared polarimetry to image the protoplanetary disk around RY Tau, revealing a thick, possibly remnant envelope structure that challenges existing disk models and suggests complex scattering and thermal processes.

Contribution

First high-resolution near-infrared polarimetric imaging of RY Tau's disk, revealing a thick, extended scattering layer not explained by standard models.

Findings

Detected a butterfly-like polarized light distribution aligned with millimeter observations.

Identified discrepancies between observed data and existing radiative transfer models.

Proposed the presence of an optically thin, geometrically thick scattering layer above the disk surface.

Abstract

We present near-infrared coronagraphic imaging polarimetry of RY Tau. The scattered light in the circumstellar environment was imaged at H-band at a high resolution (~0".05) for the first time, using Subaru-HiCIAO. The observed polarized intensity (PI) distribution shows a butterfly-like distribution of bright emission with an angular scale similar to the disk observed at millimeter wavelengths. This distribution is offset toward the blueshifted jet, indicating the presence of a geometrically thick disk or a remnant envelope, and therefore the earliest stage of the Class II evolutionary phase. We perform comparisons between the observed PI distribution and disk models with: (1) full radiative transfer code, using the spectral energy distribution (SED) to constrain the disk parameters; and (2) monochromatic simulations of scattered light which explore a wide range of parameters space to constrain the disk and dust parameters. We show that these models cannot consistently explain the observed PI distribution, SED, and the viewing angle inferred by millimeter interferometry. We suggest that the scattered light in the near-infrared is associated with an optically thin and geometrically thick layer above the disk surface, with the surface responsible for the infrared SED. Half of the scattered light and thermal radiation in this layer illuminates the disk surface, and this process may significantly affect the thermal structure of the disk.