On Shocks Driven by High-mass Planets in Radiatively Inefficient Disks. III. Observational Signatures in Thermal Emission and Scattered Light

TL;DR

This study investigates how high-mass planets in protoplanetary disks create observable shock heating signatures, affecting thermal emission and scattered light, and proposes new ways to detect such planets indirectly.

Contribution

It demonstrates that planetary shocks can be observed in disks through specific thermal and scattered light features, highlighting their role as indicators of high-mass planets.

Findings

Outer gap edge heating increases by about 50% due to planetary shocks.

Lopsided scattered light features are caused by illumination of the heated gap edge.

High-mass planets can be detected via shock signatures at wavelengths of 10 mm or longer.

Abstract

Recent observations of the protoplanetary disk around the Herbig Be star HD 100546 show two bright features in infrared (H and L' bands) at about 50 AU, with one so far unexplained. We explore the observational signatures of a high mass planet causing shock heating in order to determine if it could be the source of the unexplained infrared feature in HD 100546. More fundamentally, we identify and characterize planetary shocks as an extra, hitherto ignored, source of luminosity in transition disks. The RADMC-3D code is used to perform dust radiative transfer calculations on the hydrodynamical disk models, including volumetric heating. A stronger shock heating rate by a factor 20 would be necessary to qualitatively reproduce the morphology of the second infrared source. Instead, we find that the outer edge of the gap carved by the planet heats up by about 50% relative to the initial reference temperature, which leads to an increase in the scale height. The bulge is illuminated by the central star, producing a lopsided feature in scattered light, as the outer gap edge shows an asymmetry in density and temperature attributable to a secondary spiral arm launched not from the Lindblad resonances but from the 2:1 resonance. We conclude that high-mass planets lead to shocks in disks that may be directly observed, particularly at wavelengths of 10 mm or longer, but that they are more likely to reveal their presence in scattered light by puffing up their outer gap edges and exciting multiple spiral arms.