Accreting Circumplanetary Disks: Observational 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.