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

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

1 IPAG - Institut de Planétologie et d'Astrophysique de Grenoble

We present spectrophotometry spanning 1-5 μm of 51 Eridani b, a 2-10 {M}_{Jup} 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 L _P (3.76 μm) and new M _S (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/intermediate-opacity 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 for the planet of -5.83 to -5.93 ({log}L/{L}_⊙ ), leaving 51 Eri b in the unique position of being one of the only directly imaged planets consistent with having formed via a cold-start scenario. Comparisons of the planet SED against warm-start models indicate that the planet luminosity is best reproduced by a planet formed via core accretion with a core mass between 15 and 127 {M}_\oplus .

Keywords: instrumentation: adaptive optics; planets and satellites: atmospheres; planets and satellites: composition; planets and satellites: gaseous planets; stars: individual: 51 Eridani; Astrophysics - Earth and Planetary Astrophysics

Domains: Sciences of the Universe [physics]

Abhijith Rajan, Julien Rameau, Robert J. de Rosa, Mark S. Marley, James R. Graham, et al.. Characterizing 51 Eri b from 1 to 5 μm: A Partly Cloudy Exoplanet. The Astronomical Journal, 2017, 154, ⟨10.3847/1538-3881/aa74db⟩. ⟨insu-03692496⟩