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Constraining the radius and atmospheric properties of directly imaged exoplanets through multi-phase observations

Carrión González, Oscar and Garcia Munoz, A. and Santos, N. C. and Cabrera Perez, Juan and Csizmadia, Szilard and Rauer, Heike (2021) Constraining the radius and atmospheric properties of directly imaged exoplanets through multi-phase observations. Astronomy & Astrophysics, 655, A92. EDP Sciences. doi: 10.1051/0004-6361/202141469. ISSN 0004-6361.

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Official URL: https://www.aanda.org/articles/aa/full_html/2021/11/aa41469-21/aa41469-21.html


Context. The theory of remote sensing shows that observing a planet at multiple phase angles is a powerful strategy to characterize its atmosphere. Here, we study this observing strategy as applied to future disc-integrated direct imaging of exoplanets in reflected starlight. Aims. We analyse how the information contained in reflected-starlight spectra of exoplanets depends on the phase angle and the potential of multi-phase measurements to better constrain the atmospheric properties and the planet radius (Rp). Methods. We simulate spectra (500-900 nm) at phase angle = 37 deg, 85 deg, and 123 deg with a spectral resolution of R ~ 125-225 and signal-to-noise ratio (S/N) = 10, consistent with the expected capabilities of future direct-imaging space telescopes. Assuming a H2-He atmosphere, we use a seven-parameter model that includes the atmospheric methane abundance (fCH4), the optical properties of a cloud layer and Rp. All these parameters are assumed to be unknown a priori and are explored with a Markov chain Monte Carlo retrieval method. Results. No single-phase observation can robustly identify whether the atmosphere has clouds or not. A single-phase observation at phase angle = 123 deg and S/N = 10 can constrain Rp with a maximum error of 35%, regardless of the cloud coverage. We find that combining small (37°) and large (123°) phase angles is a generally effective strategy to break multiple parameter degeneracies. This enables us to determine the presence or absence of a cloud and its main properties, fCH4 and Rp, with higher confidence in all the explored scenarios. Other strategies, such as doubling S/N to 20 for a single-phase observation or combining small (37°) and moderate (85°) phase angles, fail to achieve this. We show that the improvements in multi-phase retrievals are associated with the shape of the scattering phase function of the cloud aerosols and that the improvement is more modest for isotropically scattering aerosols. We finally discuss that misidentifying the background gas in the retrievals of super-Earth observations leads to systematic underestimation of the absorbing gas abundance. Conclusions. Exoplanets with wide ranges of observable phase angles should be prioritized for atmospheric characterization in reflected starlight.

Item URL in elib:https://elib.dlr.de/146458/
Document Type:Article
Title:Constraining the radius and atmospheric properties of directly imaged exoplanets through multi-phase observations
AuthorsInstitution or Email of AuthorsAuthor's ORCID iDORCID Put Code
Garcia Munoz, A.AIM, CEA, CNRS, Université Paris-Saclay, Université Paris Diderot, Sorbonne Paris Cité, F-91191 Gif-sur-Yvette, Francehttps://orcid.org/0000-0003-1756-4825UNSPECIFIED
Santos, N. C.Instituto de Astrofisica e Ciencias do Espaco, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal; Departamento de Fisica e Astronomia, Faculdade de Ciencias, Universidade do Porto, Rua Campo Alegre, 4169-007 Porto, PortugalUNSPECIFIEDUNSPECIFIED
Cabrera Perez, JuanUNSPECIFIEDhttps://orcid.org/0000-0001-6653-5487UNSPECIFIED
Rauer, HeikeUNSPECIFIEDhttps://orcid.org/0000-0002-6510-1828UNSPECIFIED
Date:24 November 2021
Journal or Publication Title:Astronomy & Astrophysics
Refereed publication:Yes
Open Access:Yes
Gold Open Access:No
In ISI Web of Science:Yes
Page Range:A92
Publisher:EDP Sciences
Keywords:planets and satellites: atmospheres / planets and satellites: gaseous planets / radiative transfer
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Space Exploration
DLR - Research area:Raumfahrt
DLR - Program:R EW - Space Exploration
DLR - Research theme (Project):R - Project PLATO - PMC and Science
Location: Berlin-Adlershof
Institutes and Institutions:Institute of Planetary Research > Extrasolar Planets and Atmospheres
Institute of Planetary Research > Leitungsbereich PF
Deposited By: Cabrera Perez, Juan
Deposited On:30 Nov 2021 09:32
Last Modified:05 Dec 2023 07:22

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