Spake, JJ, Sing, DK, Wakeford, HR, Nikolov, N, Mikal-Evans, T, Deming, D, Barstow, JK, Anderson, DR ORCID: https://orcid.org/0000-0001-7416-7522, Carter, AL, Gillon, M, Goyal, JM, Hebrard, G, Hellier, C ORCID: https://orcid.org/0000-0002-3439-1439, Kataria, T, Lam, KWF, Triaud, AHMJ and Wheatley, PJ (2020) Abundance measurements of H2O and carbon-bearing species in the atmosphere of WASP-127b confirm its super-solar metallicity. Monthly Notices of the Royal Astronomical Society.

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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 super-solar, 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 super-solar CO2 volume mixing ratios, which adds to the likelihood that WASP-127b’s bulk metallicity is super-solar, since CO2 abundance is highly sensitive to atmospheric metallicity. We detect water at a significance of 13.7 σ. 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 JWST will be able to constrain WASP-127b’s C/O ratio, and may reveal the formation history of this metal-enriched, highly observable exoplanet.

Item Type: Article
Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2020 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords: techniques, spectroscopic, planets and satellites, atmospheres, stars, individual, WASP-127
Subjects: Q Science > QB Astronomy > QB799 Stars
Divisions: Faculty of Natural Sciences > School of Chemical and Physical Sciences
Depositing User: Symplectic
Date Deposited: 28 Oct 2020 15:15
Last Modified: 28 Oct 2020 15:20
URI: https://eprints.keele.ac.uk/id/eprint/8839

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