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Abundance measurements of H2O and carbon-bearing species in the atmosphere of WASP-127b confirm its supersolar metallicity

Abstract : The chemical abundances of exoplanet atmospheres may provide valuable information about the bulk compositions, formation pathways, and evolutionary histories of planets. Exoplanets with large, relatively cloud-free atmospheres, and which orbit bright stars provide the best opportunities for accurate abundance measurements. For this reason, we measured the transmission spectrum of the bright (V ~ 10.2), large (1.37 RJ), sub-Saturn mass (0.19 MJ) exoplanet WASP-127b across the near-UV to near-infrared wavelength range (0.3-5 μm), using the Hubble and Spitzer Space Telescopes. Our results show a feature-rich transmission spectrum, with absorption from Na, H2O, and CO2, and wavelength-dependent scattering from small-particle condensates. We ran two types of atmospheric retrieval models: one enforcing chemical equilibrium, and the other which fit the abundances freely. Our retrieved abundances at chemical equilibrium for Na, O, and C are all supersolar, with abundances relative to solar values of 9$^{+15}_{-6}$, 16$^{+7}_{-5}$, and 26$^{+12}_{-9}$, respectively. Despite giving conflicting C/O ratios, both retrievals gave supersolar CO2 volume mixing ratios, which adds to the likelihood that WASP-127b's bulk metallicity is supersolar, since CO2 abundance is highly sensitive to atmospheric metallicity. We detect water at a significance of 13.7σ. Our detection of Na is in agreement with previous ground-based detections, though we find a much lower abundance, and we also do not find evidence for Li or K despite increased sensitivity. In the future, spectroscopy with James Webb Space Telescope will be able to constrain WASP-127b's C/O ratio, and may reveal the formation history of this metal-enriched, highly observable exoplanet.
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https://hal-insu.archives-ouvertes.fr/insu-03748226
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Submitted on : Tuesday, August 9, 2022 - 1:58:17 PM
Last modification on : Wednesday, August 10, 2022 - 3:46:34 AM

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Jessica J. Spake, David K. Sing, Hannah R. Wakeford, Nikolay Nikolov, Thomas Mikal-Evans, et al.. Abundance measurements of H2O and carbon-bearing species in the atmosphere of WASP-127b confirm its supersolar metallicity. Monthly Notices of the Royal Astronomical Society, 2021, 500, pp.4042-4064. ⟨10.1093/mnras/staa3116⟩. ⟨insu-03748226⟩

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