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WASP-77Ab through the eyes of JWST/NIRSpec: pearls, pitfalls and lessons learned

Presentation #624.38 in the session Planetary Atmospheres - Hot Jupiters.

Published onApr 03, 2024
WASP-77Ab through the eyes of JWST/NIRSpec: pearls, pitfalls and lessons learned

The James Webb Space Telescope has provided us with data of unprecedented quality, especially for hot Jupiters, opening entire spectral windows into their atmosphere. Transmission and emission spectra carry a lot of information, which the community has already started interpreting using a plethora of atmospheric forward modelling and retrieval codes. But with great power comes great responsibility, and we need to keep a cool head with these datasets, especially considering the many degeneracies in the quest to recover atmospheric parameters from exoplanet spectra. Atmospheric retrievals have two main components: the spectral data, and the models used to reproduce it. Both have their strengths and limitations and play a part in the story told by the results. Understanding how e.g. molecular abundance measurements are informed by model assumptions rather than the pure spectral information is crucial in addition to the raw retrieval results. Different spectral channels also probe different pressure layers of the atmosphere. Quantifying this effect can give additional information on the atmospheric composition and structure, but it can also introduce a more realistic framework for the claims we can make based purely on the data. The robust tools used in our work, which are well tested in the Earth observation community, are important to set context for the results our own community will be putting forward. In this talk I will use my analysis of the new JWST/NIRSpec thermal emission observations for hot Jupiter WASP-77Ab to highlight some pearls and pitfalls of these high-quality spectral datasets. I will present our findings regarding this hot Jupiter’s intriguing atmospheric composition (subsolar metallicity and C/O ratio) and complex thermo-chemical structure. In this context, I will introduce thermal and chemical Jacobians, and advocate for their wider implementation in atmospheric retrieval codes to help inform the conclusions we draw. Finally, I will present our observations and results in context with other datasets (ground-based high-resolution spectroscopy with IGRINS, thermal emission data from HST) to illustrate the power and necessity of combining different observational methods to further mitigate for degeneracies and improve the robustness of our results.

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