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Retrieving scattering clouds and disequilibrium chemistry in the atmosphere of HR 8799e

Mollière, P. and Stolker, T. and Lacour, S. and Otten, G. P. P. L. and Shangguan, J. and Charnay, B. and Molyarova, T. and Nowak, M. and Henning, Th. and Marleau, G.-D. and Semenov, D. A. and van Dishoeck, E. and Eisenhauer, F. and Garcia, P. and García López, R. J. and Girard, J. H. and Greenbaum, A. Z. and Hinkley, S. and Kervella, P. and Kreidberg, L. and Maire, A.-L. and Nasedkin, E. and Pueyo, L. and Snellen, I. A. G. and Vigan, A. and Wang, J. and de Zeeuw, P. T. and Zurlo, A. (2020) Retrieving scattering clouds and disequilibrium chemistry in the atmosphere of HR 8799e. Astronomy and Astrophysics, 640 . Art. No. A131. ISSN 0004-6361.

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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. Aims. We aim to constrain the atmospheric properties of the directly imaged planet HR 8799e with a free retrieval approach. 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. 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_(−0.08)^(+0.07). 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. 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 CO₂ or CO iceline. As it is the innermost planet of the system, this constraint could apply to all HR 8799 planets.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Mollière, P.0000-0003-4096-7067
Stolker, T.0000-0002-5823-3072
Lacour, S.0000-0002-6948-0263
Otten, G. P. P. L.0000-0002-6717-1977
Shangguan, J.0000-0002-4569-9009
Nowak, M.0000-0001-6923-1315
Semenov, D. A.0000-0002-3913-7114
van Dishoeck, E.0000-0001-7591-1907
Garcia, P.0000-0002-1678-3535
Girard, J. H.0000-0001-8627-0404
Hinkley, S.0000-0001-8074-2562
Kervella, P.0000-0003-0626-1749
Maire, A.-L.0000-0002-2591-4138
Nasedkin, E.0000-0002-9792-3121
Pueyo, L.0000-0003-3818-408X
Snellen, I. A. G.0000-0003-1624-3667
Vigan, A.0000-0002-5902-7828
Wang, J.0000-0003-0774-6502
de Zeeuw, P. T.0000-0003-4175-3474
Zurlo, A.0000-0002-5903-8316
Additional Information:© 2020 P. Mollière et al. Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Open Access funding provided by Max Planck Society. Received 1 May 2020; Accepted 16 June 2020; Published online 27 August 2020. We would like to thank Joanna Barstow for a thorough referee report, which greatly improved the quality of this paper. We also thank the A&A editor, Emmanuel Lellouch, for additional comments. P.M. thanks M. Line, J. Zalesky, and M. Min for insightful discussions. P.M. acknowledges support from the European Research Council under the European Union’s Horizon 2020 research and innovation program under grant agreement No. 832428. T.S. acknowledges the support from the ETH Zurich Postdoctoral Fellowship Program. G.-D.M. acknowledges the support of the DFG priority program SPP 1992 “Exploring the Diversity of Extrasolar Planets” (KU 2849/7-1) and from the Swiss National Science Foundation under grant BSSGI0_155816 “PlanetsInTime”. Part of this work has been carried out within the framework of the National Centre of Competencein Research PlanetS supported by the Swiss National Science Foundation. A.V. and. G.O. acknowledge funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 757561). I.S. acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program under grant agreement No 694513. P.G. was supported by Fundação para a Ciência e a Tecnologia, with grants reference UIDB/00099/2020 and SFRH/BSAB/142940/2018. T.M. acknowledges support by the grant from the Government of the Russian Federation 075-15-2019-1875, “Study of stars with exoplanets”. D.S. acknowledges support by the Deutsche Forschungsgemeinschaft through SPP 1833: “Building a Habitable Earth” (SE 1962/6-1). A.Z. acknowledges support from the FONDECYT Iniciación en investigación project number 11190837. R.G.L. acknowledge support by Science Foundation Ireland under Grant No. 18/SIRG/559. This work benefited from the 2019 Exoplanet Summer Program in the Other Worlds Laboratory (OWL) at the University of California, Santa Cruz, a program funded by the Heising-Simons Foundation.
Funding AgencyGrant Number
European Research Council (ERC)832428
Deutsche Forschungsgemeinschaft (DFG)SPP 1992
Deutsche Forschungsgemeinschaft (DFG)KU 2849/7-1
Swiss National Science Foundation (SNSF)BSSGI0_155816
European Research Council (ERC)757561
European Research Council (ERC)694513
Fundação para a Ciência e a Tecnologia (FCT)UIDB/00099/2020
Fundação para a Ciência e a Tecnologia (FCT)SFRH/BSAB/142940/2018
Russian Federation075-15-2019-1875
Deutsche Forschungsgemeinschaft (DFG)SPP 1833
Deutsche Forschungsgemeinschaft (DFG)SE 1962/6-1
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)11190837
Science Foundation, Ireland18/SIRG/559
Heising-Simons Foundation51 Pegasi b Fellowship
Max Planck SocietyUNSPECIFIED
Subject Keywords:methods: numerical – planets and satellites: atmospheres – radiative transfer – instrumentation: spectrographs
Record Number:CaltechAUTHORS:20200828-154001508
Persistent URL:
Official Citation:Retrieving scattering clouds and disequilibrium chemistry in the atmosphere of HR 8799e. P. Mollière, T. Stolker, S. Lacour, G. P. P. L. Otten, J. Shangguan, B. Charnay, T. Molyarova, M. Nowak, Th. Henning, G.-D. Marleau, D. A. Semenov, E. van Dishoeck, F. Eisenhauer, P. Garcia, R. Garcia Lopez, J. H. Girard, A. Z. Greenbaum, S. Hinkley, P. Kervella, L. Kreidberg, A.-L. Maire, E. Nasedkin, L. Pueyo, I. A. G. Snellen, A. Vigan, J. Wang, P. T. de Zeeuw and A. Zurlo. A&A, 640 (2020) A131; DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:105154
Deposited By: Tony Diaz
Deposited On:28 Aug 2020 23:03
Last Modified:28 Aug 2020 23:03

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