Coel Hellier c.hellier@keele.ac.uk
Abundance measurements of H2O and carbon-bearing species in the atmosphere of WASP-127b confirm its super-solar metallicity
Hellier
Authors
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 s. 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.
Citation
Hellier. (2021). 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, 4042-4064. https://doi.org/10.1093/mnras/staa3116
Acceptance Date | Oct 13, 2020 |
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Publication Date | Jan 1, 2021 |
Journal | Monthly Notices of the Royal Astronomical Society |
Print ISSN | 0035-8711 |
Publisher | Oxford University Press |
Pages | 4042-4064 |
DOI | https://doi.org/10.1093/mnras/staa3116 |
Keywords | techniques, spectroscopic, planets and satellites, atmospheres, stars, individual, WASP-127 |
Publisher URL | https://doi.org/10.1093/mnras/staa3116 |
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