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51 Eri b
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Title: Characterizing 51 Eri b from 1-5 m: a partly-cloudy exoplanet
Author: 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 Duchne, 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 Lafrenire, James E. Larkin, Jrme Maire, Franck Marchis, Stanimir Metchev, Maxwell A. Millar-Blanchaer, Katie M. Morzinski, Eric L. Nielsen, Rebecca Oppenheimer, David Palmer, et al. (16 additional authors not shown)

We present spectro-photometry spanning 1-5 m 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 m) and K2 (2.10-2.40 m) spectra taken with the Gemini Planet Imager as well as an updated L_P (3.76 m) and new M_S (4.67 m) photometry from the NIRC2 Narrow camera. The new data were combined with J (1.13-1.35 m) and H (1.50-1.80 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 (logL/solar luminosity), 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 earth masses.

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RE: 51 Eridani b
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Title: Spectral and atmospheric characterization of 51 Eridani b using VLT/SPHERE
Author: M. Samland, P. Mollire, M. Bonnefoy, A.-L. Maire, F. Cantalloube, A. C. Cheetham, D. Mesa, R. Gratton, B. A. Biller, Z. Wahhaj, J. Bouwman, W. Brandner, D. Melnick, J. Carson, M. Janson, T. Henning, D. Homeier, C. Mordasini, M. Langlois, S. P. Quanz, R. van Boekel, A. Zurlo, J. E. Schlieder, H. Avenhaus, A. Boccaletti, M. Bonavita, G. Chauvin, R. Claudi, M. Cudel, S. Desidera, M. Feldt, R. Galicher, T. G. Kopytova, A.-M. Lagrange, H. Le Coroller, D. Mouillet, L. M. Mugnier, C. Perrot, E. Sissa, A. Vigan

51 Eridani b is an exoplanet around a young (20 Myr) nearby (29.4 pc) F0-type star, recently discovered by direct imaging. Being only 0.5" away from its host star it is well suited for spectroscopic analysis using integral field spectrographs. We aim to refine the atmospheric properties of this and to further constrain the architecture of the system by searching for additional companions. Using the SPHERE instrument at the VLT we extend the spectral coverage of the planet to the complete Y- to H-band range and provide photometry in the K12-bands (2.11, 2.25 micron). The object is compared to other cool and peculiar dwarfs. Furthermore, the posterior probability distributions of cloudy and clear atmospheric models are explored using MCMC. We verified our methods by determining atmospheric parameters for the two benchmark brown dwarfs Gl 570D and HD 3651B. For probing the innermost region for additional companions, archival VLT-NACO (L') SAM data is used. We present the first spectrophotometric measurements in the Y- and K-bands for the planet and revise its J-band flux to values 40% fainter than previous measurements. Cloudy models with uniform cloud coverage provide a good match to the data. We derive the temperature, radius, surface gravity, metallicity and cloud sedimentation parameter f_sed. We find that the atmosphere is highly super-solar (Fe/H~1.0) with an extended, thick cloud cover of small particles. The model radius and surface gravity suggest planetary masses of about 9 M_jup. The evolutionary model only provides a lower mass limit of >2 M_jup (for pure hot-start). The cold-start model cannot explain the planet's luminosity. The SPHERE and NACO/SAM detection limits probe the 51 Eri system at Solar System scales and exclude brown-dwarf companions more massive than 20 M_jup beyond separations of ~2.5 au and giant planets more massive than 2 M_jup beyond 9 au.

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Newly Discovered World Is Most Like Jupiter

A team of astronomers, including half a dozen from the Space Telescope Science Institute (STScI) in Baltimore, Maryland, have used the Gemini Observatory's new Gemini Planet Imager to find the most solar system-like planet ever directly imaged around another star. The planet, known as 51 Eridani b, is about two times the mass of Jupiter and orbits its host star at about 13 times the Earth-sun distance (equivalent to being between Saturn and Uranus in our solar system).
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