Another look at the dayside spectra of WASP-43b and HD 209458b: are there scattering clouds?
ArXiv 2307.08148 (2023)
Awesome SOSS: atmospheric characterization of WASP-96 b using the JWST early release observations
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 524:1 (2023) 817-834
Impact of variable photospheric radius on exoplanet atmospheric retrievals
Monthly Notices of the Royal Astronomical Society: Letters 513:1 (2022) L20-L24
Abstract:Inverse techniques are used to extract information about an exoplanet's atmosphere. These techniques are prone to biased results if the appropriate forward model is not used. One assumption used in a forward model is to assume that the radius of the planet is constant with wavelength; however, a more realistic assumption is that the photospheric radius varies with each wavelength. We explore the bias induced when attempting to extract the molecular abundance from an emission spectrum, which was generated with a variable radius. We find that for low-gravity planets, the retrieval model is not able to fit the data if a constant radius model is used. We find that biased results are obtained when studying a typical hot Jupiter in the MIRI LRS wavelength range. Finally, we show that high-gravity planets do not suffer a bias. We recommend that future spectral retrievals that interpret exoplanet emission spectra should take into account a variable radius.
How does thermal scattering shape the infrared spectra of cloudy exoplanets? A theoretical framework and consequences for atmospheric retrievals in the JWST era
Monthly Notices of the Royal Astronomical Society Oxford University Press 506:1 (2021) 1309-1332
Abstract:Observational studies of exoplanets are suggestive of a ubiquitous presence of clouds. The current modelling techniques used in emission to account for the clouds tend to require prior knowledge of the cloud condensing species and often do not consider the scattering effects of the cloud. We explore the effects that thermal scattering has on the emission spectra by modelling a suite of hot Jupiter atmospheres with varying cloud single-scattering albedos (SSAs) and temperature profiles. We examine cases ranging from simple isothermal conditions to more complex structures and physically driven cloud modelling. We show that scattering from nightside clouds would lead to brightness temperatures that are cooler than the real atmospheric temperature if scattering is unaccounted for. We show that scattering can produce spectral signatures in the emission spectrum even for isothermal atmospheres. We identify the retrieval degeneracies and biases that arise in the context of simulated JWST spectra when the scattering from the clouds dominates the spectral shape. Finally, we propose a novel method of fitting the SSA spectrum of the cloud in emission retrievals, using a technique that does not require any prior knowledge of the cloud chemical or physical properties.
Understanding and mitigating biases when studying inhomogeneous emission spectra with JWST
Monthly Notices of the Royal Astronomical Society Royal Astronomical Society 493:3 (2020) 4342-4354,