Mon. Not. R. Astron. Soc., 500, 4042-4064 (2021/January-3)
Abundance measurements of H2O and carbon-bearing species in the atmosphere of WASP-127b confirm its supersolar metallicity.
SPAKE J.J., SING D.K., WAKEFORD H.R., NIKOLOV N., MIKAL-EVANS T., DEMING D., BARSTOW J.K., ANDERSON D.R., CARTER A.L., GILLON M., GOYAL J.M., HEBRARD G., HELLIER C., KATARIA T., LAM K.W.F., TRIAUD A.H.M.J. and WHEATLEY P.J.
Abstract (from CDS):
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.
© 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
techniques: spectroscopic - planets and satellites: atmospheres - stars: individual: WASP-127
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