Surface Geometry of Protoplanetary Disks Inferred From Near-Infrared Imaging Polarimetry

TL;DR

This paper introduces a novel method to analyze the surface geometry of protoplanetary disks using near-infrared polarimetric imaging, revealing structures linked to planet formation.

Contribution

A new differential equation-based approach to infer disk surface geometry from polarized intensity data in near-infrared imaging.

Findings

Local maxima in polarized intensity correlate with concave-up disk surface structures.

Inner gaps do not necessarily imply vertical inner walls; disks can be shadowed.

Spiral and ring structures may indicate ongoing planet formation.

Abstract

We present a new method of analysis for determining the surface geometry of five protoplanetary disks observed with near-infrared imaging polarimetry using Subaru-HiCIAO. Using as inputs the observed distribution of polarized intensity (PI), disk inclination, assumed properties for dust scattering, and other reasonable approximations, we calculate a differential equation to derive the surface geometry. This equation is numerically integrated along the distance from the star at a given position angle. We show that, using these approximations, the local maxima in the PI distribution of spiral arms (SAO 206462, MWC 758) and rings (2MASS J16042165-2130284, PDS 70) are associated with local concave-up structures on the disk surface. We also show that the observed presence of an inner gap in scattered light still allows the possibility of a disk surface that is parallel to the light path from the star, or a disk that is shadowed by structures in the inner radii. Our analysis for rings does not show the presence of a vertical inner wall as often assumed in studies of disks with an inner gap. Finally, we summarize the implications of spiral and ring structures as potential signatures of ongoing planet formation.