methods: numerical; planets and satellites: atmospheres; radiative transfer; instrumentation: spectrographs; Astrophysics - Earth and Planetary Astrophysics
Abstract :
[en] Context. Clouds are ubiquitous in exoplanet atmospheres and they represent a challenge for the model interpretation of their spectra. When generating a large number of model spectra, complex cloud models often prove too costly numerically, whereas more efficient models may be overly simplified. <BR /> Aims: We aim to constrain the atmospheric properties of the directly imaged planet HR 8799e with a free retrieval approach. <BR /> Methods: We used our radiative transfer code petitRADTRANS for generating the spectra, which we coupled to the PyMultiNest tool. We added the effect of multiple scattering which is important for treating clouds. Two cloud model parameterizations are tested: the first incorporates the mixing and settling of condensates, the second simply parameterizes the functional form of the opacity. <BR /> Results: In mock retrievals, using an inadequate cloud model may result in atmospheres that are more isothermal and less cloudy than the input. Applying our framework on observations of HR 8799e made with the GPI, SPHERE, and GRAVITY, we find a cloudy atmosphere governed by disequilibrium chemistry, confirming previous analyses. We retrieve that C/O = 0.60[SUB]-0.08[/SUB][SUP]+0.07[/SUP]. Other models have not yet produced a well constrained C/O value for this planet. The retrieved C/O values of both cloud models are consistent, while leading to different atmospheric structures: either cloudy or more isothermal and less cloudy. Fitting the observations with the self-consistent Exo-REM model leads to comparable results, without constraining C/O. <BR /> Conclusions: With data from the most sensitive instruments, retrieval analyses of directly imaged planets are possible. The inferred C/O ratio of HR 8799e is independent of the cloud model and thus appears to be a robust. This C/O is consistent with stellar, which could indicate that the HR 8799e formed outside the CO[SUB]2[/SUB] or CO iceline. As it is the innermost planet of the system, this constraint could apply to all HR 8799 planets.
Stolker, T.; Institute for Particle Physics and Astrophysics, ETH Zurich, Wolfgang-Pauli-Strasse 27, 8093, Zurich, Switzerland
Lacour, S.; LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Univ. Paris Diderot, Sorbonne Paris Cit, 5 place Jules Janssen, 92195, Meudon, France ; Max Planck Institute for extraterrestrial Physics, Giessenbachstraße 1, 85748, Garching, Germany ; European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748, Garching, Germany
Otten, G. P. P. L.; Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
Shangguan, J.; Max Planck Institute for extraterrestrial Physics, Giessenbachstraße 1, 85748, Garching, Germany
Charnay, B.; LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Univ. Paris Diderot, Sorbonne Paris Cit, 5 place Jules Janssen, 92195, Meudon, France
Molyarova, T.; Institute of Astronomy, Russian Academy of Sciences, 48 Pyatnitskaya St., Moscow, 119017, Russia
Nowak, M.; Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK ; Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK
Henning, Th; Max-Planck-Institut für Astronomie, Königstuhl 17, 69117, Heidelberg, Germany
Marleau, G.-D.; Institut für Astronomie und Astrophysik, Universität Tübingen, Auf der Morgenstelle 10, 72076, Tübingen, Germany ; Center for Space and Habitability, Universität Bern, Gesellschaftsstrasse 6, 3012, Bern, Switzerland ; Max-Planck-Institut für Astronomie, Königstuhl 17, 69117, Heidelberg, Germany
Semenov, D. A.; Max-Planck-Institut für Astronomie, Königstuhl 17, 69117, Heidelberg, Germany ; Department of Chemistry, Ludwig-Maximilians-Universität, Butenandtstraße 5-13, 81377, Munich, Germany
van Dishoeck, E.; Leiden Observatory, Leiden University, Postbus 9513, 2300 RA, Leiden, The Netherlands ; Max Planck Institute for extraterrestrial Physics, Giessenbachstraße 1, 85748, Garching, Germany
Eisenhauer, F.; Max Planck Institute for extraterrestrial Physics, Giessenbachstraße 1, 85748, Garching, Germany
Garcia, P.; CENTRA, Centro de Astrofísica e Gravitação, Instituto Superior Técnico, Avenida Rovisco Pais 1, 1049, Lisboa, Portugal ; Universidade do Porto, Faculdade de Engenharia, Rua Dr. Roberto Frias, 4200-465, Porto, Portugal
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Girard, J. H.; Space Telescope Science Institute, Baltimore, MD, 21218, USA
Greenbaum, A. Z.; Department of Astronomy, University of Michigan, Ann Arbor, MI, 48109, USA
Hinkley, S.; University of Exeter, Physics Building, Stocker Road, Exeter, EX4 4QL, UK
Kervella, P.; LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Univ. Paris Diderot, Sorbonne Paris Cit, 5 place Jules Janssen, 92195, Meudon, France
Kreidberg, L.; Max-Planck-Institut für Astronomie, Königstuhl 17, 69117, Heidelberg, Germany
Maire, Anne-Lise ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > PSILab
Nasedkin, E.; Max-Planck-Institut für Astronomie, Königstuhl 17, 69117, Heidelberg, Germany
Pueyo, L.; Space Telescope Science Institute, Baltimore, MD, 21218, USA
Snellen, I. A. G.; Leiden Observatory, Leiden University, Postbus 9513, 2300 RA, Leiden, The Netherlands
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