How Spirals and Gaps Driven by Companions in Protoplanetary Disks Appear in Scattered Light at Arbitrary Viewing Angles

TL;DR

This study uses 3D simulations to analyze how planet-induced spiral arms and gaps in protoplanetary disks appear at various viewing angles in near-infrared scattered light, revealing complex morphologies.

Contribution

It provides the first detailed analysis of how inclination affects the observable features of planet-induced structures in disks, challenging simple deprojection assumptions.

Findings

Spiral arms can appear as one or two arms depending on viewing angle.

Disk rings outside gaps can mimic spiral arms at high inclinations.

Inclined views cannot be accurately deprojected into face-on views using simple methods.

Abstract

Direct imaging observations of protoplanetary disks at near-infrared (NIR) wavelengths have revealed structures of potentially planetary origin. Investigations of observational signatures from planet-induced features have so far focused on disks viewed face-on. Combining 3D hydrodynamics and radiative transfer simulations, we study how the appearance of the spiral arms and the gap produced in a disk by a companion varies with inclination and position angle in NIR scattered light. We compare the cases of a $3M_{\rm J}$ and a $0.1M_{\odot}$ companion, and make predictions suitable for testing with Gemini/GPI, VLT/NACO/SPHERE, and Subaru/HiCIAO/SCExAO. We find that the two trailing arms produced by an external perturber can have a variety of morphologies in inclined systems - they may appear as one trailing arm; two trailing arms on the same side of the disk; or two arms winding in opposite directions. The disk ring outside a planetary gap may also mimic spiral arms when viewed at high inclinations. We suggest potential explanations for the features observed in HH 30, HD 141569 A, AK Sco, HD 100546, and AB Aur. We emphasize that inclined views of companion-induced features cannot be converted into face-on views using simple and commonly practiced image deprojections.