Accreting Circumplanetary Disks: Observational Signatures

I calculate the spectral energy distributions of accreting circumplanetary disks using atmospheric radiative transfer models. Circumplanetary disks only accreting at 10^-10 M _⊙ yr^-1 around a 1 M_J planet can be brighter than the planet itself. A moderately accreting circumplanetary disk (\dot{M}∼ 10^-8 M_⊙ yr^-1; enough to form a 10 M_J planet within 1 Myr) around a 1 M_J planet has a maximum temperature of ~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 toward longer wavelengths than those of brown dwarfs or planets. If young planets have strong magnetic fields (gsim100 G), fields may truncate slowly accreting circumplanetary disks (\dot{M}≲ 10^-9 M_⊙ 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.