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

July 2017 • 2017AJ....154...10R

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

Abstract • 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.

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Alexandra Greenbaum

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