Spectral Energy Distributions of Accreting Protoplanets

TL;DR

This paper models the spectral energy distributions of accreting protoplanets to understand their appearance and compare with observations, suggesting many transition disks likely host detectable bright protoplanets.

Contribution

It provides synthetic spectral models for accreting protoplanets across evolutionary stages and compares them with observed candidates, highlighting detection challenges.

Findings

Observed fluxes are compatible with accreting protoplanets.

Extended structures in observations are difficult to reconcile with compact protoplanet emission.

Larger telescopes could reveal more protoplanets in transition disks.

Abstract

Planets are often invoked as the cause of inferred gaps or inner clearings in transition disks. These putative planets would interact with the remnant circumstellar disk, accreting gas and generating substantial luminosity. Here I explore the expected appearance of accreting protoplanets at a range of evolutionary states. I compare synthetic spectral energy distributions with the handful of claimed detections of substellar-mass companions in transition disks. While observed fluxes of candidate companions are generally compatible with accreting protoplanets, challenges remain in reconciling the extended structure inferred in observed objects with the compact emission expected from protoplanets or circumplanetary disks. I argue that a large fraction of transition disks should harbor bright protoplanets, and that more may be detected as larger telescopes open up additional parameter space.