Evidence for a Circumplanetary Disk around Protoplanet PDS 70 b

We present the first observational evidence for a circumplanetary disk (CPD) around the protoplanet PDS 70 b, based on a new spectrum in the K-band acquired with Very Large Telescope/SINFONI. We tested three hypotheses to explain the spectrum: atmospheric emission from the planet with either (1) a single value of extinction, (2) a variable extinction, and (3) a combined atmospheric and CPD model. Goodness-of-fit indicators favor the third option, suggesting that circumplanetary material contributes excess thermal emission-most prominent at lambda greater than or similar to 2.3 mu m. Inferred accretion rates (similar to 10(-7.8)-10(-7.3) M-J yr(-1)) are compatible with observational constraints based on the H alpha and Br gamma, lines. For the planet, we derive an effective temperature of 1500-1600 K, surface gravity log(g) similar to 4.0, radius similar to 1.6R(J), mass similar to 10M (J), and possible thick clouds. Models with variable extinction lead to slightly worse fits. However, the amplitude (Delta A(v) greater than or similar to 3 mag) and timescale of variation (less than or similar to years) required for the extinction would also suggest circumplanetary material.