BOWIE-ALIGN: substellar metallicity and carbon depletion in the aligned TrES-4b with JWST NIRSpec transmission spectroscopy
File(s)
Published version
Author(s)
Type
Journal Article
Abstract
The formation and migration history of a planet is expected to be imprinted in its atmosphere, in particular its carbon-to-oxygen (C/O) ratio and metallicity. The BOWIE-ALIGN (Bristol, Oxford, Warwick, Imperial, Exeter – A spectral Light Investigation into gas Giant origiNs) programme is performing a comparative study of JWST spectra of four aligned and four misaligned hot Jupiters, with the aim of characterizing their atmospheres and corroborating the link between the observables and the formation history. In this work, we present the $2.8-5.2$ µm transmission spectrum of TrES-4 b, a hot Jupiter with an orbit aligned with the rotation axis of its F-type host star. Using free chemistry atmospheric retrievals, we report a confident detection of H$_2$O at an abundance of $\log _\mathrm{H_2O}=-2.98^{+0.68}_{-0.73}$ at a significance of $8.4\sigma$. We also find evidence for CO and small amounts of CO$_2$, retrieving abundances $\log X_\mathrm{CO}= -3.76^{+0.89}_{-1.01}$ and $\log X_\mathrm{CO_2}= -6.86^{+0.62}_{-0.65}$ ($3.1\sigma$ and $4.0\sigma$, respectively). The observations are consistent with the atmosphere being in chemical equilibrium; our retrievals yield $\mathrm{C/O}$ between $0.30-0.42$ and constrain the atmospheric metallicity to the range $0.4-0.7\times$ solar. The inferred substellar properties (C/O and metallicity) challenge traditional models, and could have arisen from an oxygen-rich gas accretion scenario, or a combination of low-metallicity gas and carbon-poor solid accretion.
Date Issued
2025-05-01
Date Acceptance
2025-03-26
Citation
Monthly Notices of the Royal Astronomical Society, 2025, 539 (2), pp.1381-1403
ISSN
0035-8711
Publisher
Oxford University Press (OUP)
Start Page
1381
End Page
1403
Journal / Book Title
Monthly Notices of the Royal Astronomical Society
Volume
539
Issue
2
Copyright Statement
© 2025 The Author(s). Published by Oxford University Press on behalf of 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.
License URL
Identifier
10.1093/mnras/staf530
Subjects
techniques
spectroscopic -exoplanets -planets and satellites
atmospheres -planets and satellites
compositionplanets and satellites
gaseous planets
Publication Status
Published
Date Publish Online
2025-04-01