Accreting Circumplanetary Disks: Observational Signatures

TL;DR

This paper models the spectral energy distributions of accreting circumplanetary disks, highlighting their brightness at various wavelengths and proposing observational signatures to distinguish them from brown dwarfs and planets.

Contribution

It provides detailed radiative transfer models of circumplanetary disks and identifies key observational signatures across different wavelengths for detecting and characterizing these disks.

Findings

Disks accreting at 10^{-10} M_sun/yr can outshine their planets.

Mid-infrared photometry is crucial for distinguishing disks from brown dwarfs.

Magnetic fields may lead to magnetospheric accretion signatures.

Abstract

I calculate the spectral energy distributions (SEDs) of accreting circumplanetary disks using atmospheric radiative transfer models. Circumplanetary disks only accreting at $10^{-10} M_{\odot} yr^{-1}$ around a 1 M$_{J}$ planet can be brighter than the planet itself. A moderately accreting circumplanetary disk ($\dot{M}\sim 10^{-8}M_{\odot} yr^{-1}$; enough to form a 10 M$_{J}$ planet within 1 Myr) around a 1 M$_{J}$ planet has a maximum temperature of $\sim$2000 K, and at near-infrared wavelengths ($J$, $H$, $K$ bands), this disk is as bright as a late M-type brown dwarf or a 10 M$_{J}$ planet with a "hot start". To use direct imaging to find the accretion disks around low mass planets (e.g., 1 M$_{J}$) and distinguish them from brown dwarfs or hot high mass planets, it is crucial to obtain photometry at mid-infrared bands ($L'$, $M$, $N$ bands) because the emission from circumplanetary disks falls off more slowly towards longer wavelengths than those of brown dwarfs or planets. If young planets have strong magnetic fields ($\gtrsim$100 G), fields may truncate slowly accreting circumplanetary disks ($\dot{M}\lesssim10^{-9} M_{\odot} yr^{-1}$) and lead to magnetospheric accretion, which can provide additional accretion signatures, such as UV/optical excess from the accretion shock and line emission.