Title Characterizing 51 Eri b from 1 to 5 μm : A Partly Cloudy Exoplanet Permalink

We present spectrophotometry spanning 1–5 μmof 51 Eridani b, a 2–10MJup planet discovered by the Gemini Planet Imager Exoplanet Survey. In this study, we present new K1 (1.90–2.19 μm) and K2 (2.10–2.40 μm) spectra taken with the Gemini Planet Imager as well as an updated LP(3.76 μm) and new MS(4.67 μm) photometry from the NIRC2 Narrow camera. The new data were combined with J(1.13–1.35 μm) and H(1.50–1.80 μm) spectra from the discovery epoch with the goal of better characterizing the planet properties. The 51Erib photometry is redder than field brown dwarfs as well as known young T-dwarfs with similar spectral type (between T4 and T8), and we propose that 51 Eri b might be in the process of undergoing the transition from L-type to T-type. We used two complementary atmosphere model grids including either deep iron/silicate clouds or sulfide/salt clouds in the photosphere, spanning a range of cloud properties, including fully cloudy, cloud-free, and patchy/intermediateopacity clouds. The model fits suggest that 51Erib has an effective temperature ranging between 605 and 737 K, a solar metallicity, and a surface gravity of log(g) = 3.5–4.0 dex, and the atmosphere requires a patchy cloud atmosphere to model the spectral energy distribution (SED). From the model atmospheres, we infer a luminosity The Astronomical Journal, 154:10 (20pp), 2017 July https://doi.org/10.3847/1538-3881/aa74db © 2017. The American Astronomical Society. All rights reserved. 35 NASA Hubble Fellow.