Characterizing 51 Eri b from 1-5 $μ$m: a partly-cloudy exoplanet
Creators: name: Rajan, Abhijith
name: Rameau, Julien
name: De Rosa, Robert J.
name: Marley, Mark S.
name: Graham, James R.
name: Macintosh, Bruce
name: Marois, Christian
name: Morley, Caroline
name: Patience, Jennifer
name: Pueyo, Laurent
name: Saumon, Didier
name: Ward-Duong, Kimberly
name: Ammons, S. Mark
name: Arriaga, Pauline
name: Bailey, Vanessa P.
name: Barman, Travis
name: Bulger, Joanna
name: Burrows, Adam S.
name: Chilcote, Jeffrey
name: Cotten, Tara
name: Czekala, Ian
name: Doyon, Rene
name: Duchêne, Gaspard
name: Esposito, Thomas M.
name: Fitzgerald, Michael P.
name: Follette, Katherine B.
name: Fortney, Jonathan J.
name: Goodsell, Stephen J.
name: Greenbaum, Alexandra Z.
name: Hibon, Pascale
name: Hung, Li-Wei
name: Ingraham, Patrick
name: Johnson-Groh, Mara
name: Kalas, Paul
name: Konopacky, Quinn
name: Lafrenière, David
name: Larkin, James E.
name: Maire, Jérôme
name: Marchis, Franck
name: Metchev, Stanimir
name: Millar-Blanchaer, Maxwell A.
name: Morzinski, Katie M.
name: Nielsen, Eric L.
name: Oppenheimer, Rebecca
name: Palmer, David
name: Patel, Rahul I.
name: Perrin, Marshall
name: Poyneer, Lisa
name: Rantakyrö, Fredrik T.
name: Ruffio, Jean-Baptiste
name: Savransky, Dmitry
name: Schneider, Adam C.
name: Sivaramakrishnan, Anand
name: Song, Inseok
name: Soummer, Rémi
name: Thomas, Sandrine
name: Vasisht, Gautam
name: Wallace, J. Kent
name: Wang, Jason J.
name: Wiktorowicz, Sloane
name: Wolff, Schuyler
Publisher: name: arXiv
Year: 2017
Subjects: subject: Earth and Planetary Astrophysics (astro-ph.EP)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: We present spectro-photometry spanning 1-5 $μ$m of 51 Eridani b, a 2-10 M$_\text{Jup}$ planet discovered by the Gemini Planet Imager Exoplanet Survey. In this study, we present new $K1$ (1.90-2.19 $μ$m) and $K2$ (2.10-2.40 $μ$m) spectra taken with the Gemini Planet Imager as well as an updated $L_P$ (3.76 $μ$m) and new $M_S$ (4.67 $μ$m) photometry from the NIRC2 Narrow camera. The new data were combined with $J$ (1.13-1.35 $μ$m) and $H$ (1.50-1.80 $μ$m) spectra from the discovery epoch with the goal of better characterizing the planet properties. 51 Eri b photometry is redder than field brown dwarfs as well as known young T-dwarfs with similar spectral type (between T4-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/intermediate opacity clouds. Model fits suggest that 51 Eri b has an effective temperature ranging between 605-737 K, a solar metallicity, a surface gravity of $\log$(g) = 3.5-4.0 dex, and the atmosphere requires a patchy cloud atmosphere to model the SED. From the model atmospheres, we infer a luminosity for the planet of -5.83 to -5.93 ($\log L/L_{\odot}$), leaving 51 Eri b in the unique position as being one of the only directly imaged planet consistent with having formed via cold-start scenario. Comparisons of the planet SED against warm-start models indicates that the planet luminosity is best reproduced by a planet formed via core accretion with a core mass between 15 and 127 M$_{\oplus}$.
description: 27 pages, 19 figures, Accepted for publication in The Astronomical Journal