Vol. 643
10. Planets and planetary systems

MIRACLES: atmospheric characterization of directly imaged planets and substellar companions at 4-5 μm. II. Constraints on the mass and radius of the enshrouded planet PDS 70 b

The young (~5 Myr) T Tauri star PDS 70 is an emblematic object for the study of planetary formation. It holds a gapped circumstellar disk in which two embedded planets (PDS 70 b and c) have been directly imaged and show evidence for gas accretion through detection of H alpha emission. The atmospheric and circumplanetary characteristics of these accreting young planets remain poorly understood, and a previous study of the spectral energy distribution of PDS 70 b has suggested a possible combination of emission from a planet atmosphere and a circumplanetary disk. Using VLT/NACO, Stolker et al. report the first detection of PDS 70 b in the Brα and M' filters as well as a tentative detection of PDS 70 c in Brα. PDS 70 b appears significantly redder than any previously imaged planets and brown dwarfs in the color (K-M') - magnitude (M') diagram. Fitting the resulting 1-5 um spectral energy distribution leads to a photospheric temperature Teff = 1193 +/- 20 K and a photospheric radius R = 3.0 +/- 0.2 R_J. In addition, by comparing the object's luminosity with predictions from planet structure models, and taking into account the accretion luminosity as constrained by H alpha, the authors were able to constrain the mass of PDS 70 b to Mp ≈ 0.5–1.5 M_J and its physical radius to Rp ≈ 1–2.5 R_J. The discrepancy between the photospheric and planetary radii may indicate that the planet is embedded in an extended dusty environment, muting molecular features in the object's spectrum, which implies that PDS 70 b not only accretes gas but is also continuously replenished by dust.