V. Christiaens, F. Cantalloube, S. Casassus, D. J. Price, O. Absil, C. Pinte, J. Girard, M. Montesinos
We present the first observational evidence for a circumplanetary disc around the protoplanet PDS~70~b, based on a new spectrum in the KK band acquired with VLT/SINFONI. We tested three hypotheses to explain the spectrum: Atmospheric emission from the planet with either (1) a single value of extinction or (2) variable extinction, and (3) a combined atmospheric and circumplanetary disc model. Goodness-of-fit indicators favour the third option, suggesting circumplanetary material contributing excess thermal emission --- most prominent at λ≳2.3μλ≳2.3μm. Inferred accretion rates (∼10−7.8∼10−7.8--10−7.3MJ10−7.3MJ yr−1−1) are compatible with observational constraints based on the Hααand Brγγ lines. For the planet, we derive an effective temperature of 1500--1600 K, surface gravity log(g)∼4.0log(g)∼4.0, radius ∼1.6RJ∼1.6RJ, mass ∼10MJ∼10MJ, and possible thick clouds. Models with variable extinction lead to slightly worse fits. However, the amplitude (ΔAV≳3ΔAV≳3mag) and timescale of variation (≲≲~years) required for the extinction would also suggest circumplanetary material.