Detectability of embedded protoplanets from hydrodynamical simulations

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Abstract

We predict magnitudes for young planets embedded in transition discs, still affected by extinction due to material in the disc. We focus on Jupiter-sized planets at a late stage of their formation, when the planet has carved a deep gap in the gas and dust distributions and the disc starts to being transparent to the planet flux in the infrared (IR). Column densities are estimated by means of three-dimensional hydrodynamical models, performed for several planet masses. Expected magnitudes are obtained by using typical extinction properties of the disc material and evolutionary models of giant planets. For the simulated cases located at 5.2 au in a disc with a local unperturbed surface density of 127 g cm$^{-2}$⁠, a 1 $M_J$ planet is highly extinct in the J, H, and K bands, with predicted absolute magnitudes ≥ 50 mag. In the L and M bands, extinction decreases, with planet magnitudes between 25 and 35 mag. In the N band, due to the silicate feature on the dust opacities, the expected magnitude increases to ∼40 mag. For a 2 $M_J$ planet, the magnitudes in the J, H, and K bands are above 22 mag, while for the L, M, and N bands, the planet magnitudes are between 15 and 20 mag. For the 5 $M_J$ planet, extinction does not play a role in any IR band, due to its ability to open deep gaps. Contrast curves are derived for the transition discs in CQ Tau, PDS 70, HL Tau, TW Hya, and HD 163296. Planet mass upper limits are estimated for the known gaps in the last two systems.