Characterizing 51 Eri b from 1-5 \(\mu\)m: a partly-cloudy exoplanet

• Published in: arXiv.org 2017-05
• Main 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, tney, Jonathan J, Goodsell, Stephen J, Greenbaum, Alexandra Z, Hibon, Pascale, Li-Wei, Hung, Ingraham, Patrick, Johnson-Groh, Mara, Kalas, Paul, Quinn Konopacky, 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, Jean-Baptiste Ruffio, 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
• Format: Article
• Language: English
• Subjects: Atmospheric models; Brown dwarf stars; Clouds; Cold starts; Deposition; Extrasolar planets; Luminosity; Metallicity; Photometry; Photosphere; Planet detection; Planetary atmospheres; Spectra
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1705.03887

We present spectro-photometry spanning 1-5 \(\mu\)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 \(\mu\)m) and \(K2\) (2.10-2.40 \(\mu\)m) spectra taken with the Gemini Planet Imager as well as an updated \(L_P\) (3.76 \(\mu\)m) and new \(M_S\) (4.67 \(\mu\)m) photometry from the NIRC2 Narrow camera. The new data were combined with \(J\) (1.13-1.35 \(\mu\)m) and \(H\) (1.50-1.80 \(\mu\)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\(_{\oplus}\).