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Exoplanets with JWST: degeneracy, systematics and how to avoid them

Barstow, JK; Irwin, PGJ; Kendrew, S; Aigrain, S; (2016) Exoplanets with JWST: degeneracy, systematics and how to avoid them. In: MacEwen, HA and Fazio, GG and Lystrup, M and Batalha, N and Siegler, N and Tong, EC, (eds.) Space Telescopes and Instrumentation 2016: Optical, Infrared, and Millimeter Wave [Proceedings]. (pp. 99043P1-99043P13). Society of Photo-Optical Instrumentation Engineers Green open access

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Abstract

The high sensitivity and broad wavelength coverage of the James Webb Space Telescope will transform the field of exoplanet transit spectroscopy. Transit spectra are inferred from minute, wavelength-dependent variations in the depth of a transit or eclipse as the planet passes in front of or is obscured by its star, and the spectra contain information about the composition, structure and cloudiness of exoplanet atmospheres. Atmospheric retrieval is the preferred technique for extracting information from these spectra, but the process can be confused by astrophysical and instrumental systematic noise. We present results of retrieval tests based on synthetic, noisy JWST spectra, for clear and cloudy planets and active and inactive stars. We find that the ability to correct for stellar activity is likely to be a limiting factor for cloudy planets, as the effects of unocculted star spots may mimic the presence of a scattering slope due to clouds. We discuss the pros and cons of the available JWST instrument combinations for transit spectroscopy, and consider the effect of clouds and aerosols on the spectra. Aerosol high in a planet’s atmosphere obscures molecular absorption features in transmission, reducing the information content of spectra in wavelength regions where the cloud is optically thick. We discuss the usefulness of particular wavelength regions for identifying the presence of cloud, and suggest strategies for solving the highly-degenerate retrieval problem for these objects.

Type: Proceedings paper
Title: Exoplanets with JWST: degeneracy, systematics and how to avoid them
Event: Space Telescopes and Instrumentation 2016: Optical, Infrared, and Millimeter Wave, 26 June 2016, Edinburgh, United Kingdom
Location: Edinburgh
Dates: 26 June 2016 - 01 July 2016
ISBN-13: 9781510601871
Open access status: An open access version is available from UCL Discovery
DOI: 10.1117/12.2232543
Publisher version: http://dx.doi.org/10.1117/12.2232543
Language: English
Additional information: Copyright © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE). One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.
Keywords: radiative transfer, planetary science
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/1529969
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