BOWIE-ALIGN: weak spectral features in KELT-7b’s JWST NIRSpec/G395H transmission spectrum imply a high cloud deck or a low-metallicity atmosphere
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Author(s)
Type
Journal Article
Abstract
Hot Jupiters and their atmospheres are prime targets for transmission spectroscopy due to their extended atmospheres and the corresponding large signal-to-noise, providing the best possible constraints for the atmospheric carbon-to-oxygen (C/O) ratio and metallicity of exoplanets. Within BOWIE-ALIGN, we aim to compare JWST spectra of a sample of orbitally aligned and misaligned hot Jupiters orbiting F-type stars to probe the link between hot Jupiter atmospheres and planet formation history. Here, we present a near-infrared transmission spectrum of the aligned planet KELT-7b using one transit observed with JWST NIRSpec/G395H. We find weak features, only tentative evidence for H2O and CO2 in the atmosphere of KELT-7b. This poses a challenge to constrain the atmospheric properties of KELT-7b and two possible scenarios emerge from equilibrium chemistry and free chemistry retrievals: a high-altitude cloud deck muting all features or an extremely low metallicity atmosphere, respectively. The retrieved C/O ratios from our data reductions range from 0.43 − 0.74, while the atmospheric metallicity is suggested to be solar to super-solar (1 − 16 × solar). Although these wide constraints prevent detailed conclusions about KELT-7b’s formation history, a solar-to-super-solar metallicity would imply the accretion of solid material during its formation, which is valuable information for the survey’s wider goals of understanding the relative importance of gaseous to solid accretion.
Date Issued
2025-11-01
Date Acceptance
2025-09-09
Citation
Monthly Notices of the Royal Astronomical Society, 2025, 543 (3), pp.2442-2462
ISSN
0035-8711
Publisher
Oxford University Press
Start Page
2442
End Page
2462
Journal / Book Title
Monthly Notices of the Royal Astronomical Society
Volume
543
Issue
3
Copyright Statement
© The Author(s) 2025. Published by Oxford University Press on behalf of The Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited
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Publication Status
Published
Article Number
staf1535
Date Publish Online
2025-09-16