Confirmation of Subsolar Metallicity for WASP-77Ab from JWST Thermal Emission Spectroscopy

We present the dayside thermal emission spectrum of WASP-77Ab from 2.8 to 5.2 μ m as observed with the NIRSpec instrument on the James Webb Space Telescope (JWST). WASP-77Ab was previously found to have a subsolar metallicity and a solar carbon-to-oxygen (C/O) ratio from H 2 O and CO absorption line...

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Bibliographic Details
Published in:Astrophysical journal. Letters 2023-08, Vol.953 (2), p.L24
Main Authors: August, Prune C., Bean, Jacob L., Zhang, Michael, Lunine, Jonathan, Xue, Qiao, Line, Michael, Smith, Peter C. B.
Format: Article
Language:English
Subjects:
Abundance
Brightness temperature
Carbon dioxide
Composition
Emission spectra
Emission spectroscopy
Exoplanet atmospheres
Exoplanets
Extrasolar planets
Field cameras
Gas giant planets
High resolution
Hubble Space Telescope
James Webb Space Telescope
Jupiter
Metallicity
Oxygen
Space telescopes
Spectroscopy
Spectrum analysis
Thermal emission
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Summary:We present the dayside thermal emission spectrum of WASP-77Ab from 2.8 to 5.2 μ m as observed with the NIRSpec instrument on the James Webb Space Telescope (JWST). WASP-77Ab was previously found to have a subsolar metallicity and a solar carbon-to-oxygen (C/O) ratio from H 2 O and CO absorption lines detected using high-resolution spectroscopy. By performing atmospheric retrievals on the JWST spectrum assuming chemical equilibrium, we find a subsolar metallicity [M/H] = − 0.91 − 0.16 + 0.24 and C/O ratio 0.36 − 0.09 + 0.10 . We identify H 2 O and CO and constrain their abundances, and we find no CO 2 in the spectrum. The JWST and high-resolution spectroscopy results agree within ∼1 σ for the metallicity and within 1.8 σ for the C/O ratio. However, our results fit less well in the picture painted by the shorter wavelength spectrum measured by Hubble Space Telescope Wide Field Camera 3. Comparing the JWST thermal emission spectra of WASP-77Ab and HD 149026b shows that both hot Jupiters have nearly identical brightness temperatures in the near-infrared but distinctly different atmospheric compositions. Our results reaffirm high-resolution spectroscopy as a powerful and reliable method to measure molecular abundances. Our results also highlight the incredible diversity of hot Jupiter atmospheric compositions.
ISSN:2041-8205
2041-8213
DOI:10.3847/2041-8213/ace828