A super-solar metallicity atmosphere for WASP-127b revealed by transmission spectroscopy from HST and Spitzer

Jessica J. Spake, David K. Sing, Hannah R. Wakeford, Nikolay Nikolov, Thomas Mikal-Evans, Drake Deming, Joanna Barstow, David R. Anderson, Aarynn L. Carter, Michael Gillon, Jayesh M. Goyal, Guillaume Hebrard, Coel Hellier, Tiffany Kataria, Kristine W. F. Lam, A. H. M. J. Triaud

Research output: Contribution to journalArticlepeer-review

Abstract

The chemical abundances of exoplanet atmospheres may provide valuable information about the bulk compositions, formation pathways, and evolutionary histories of planets. Exoplanets which have 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 (1.37RJ), sub-Saturn mass (0.19MJ) exoplanet WASP-127b across the near-UV to near-infrared wavelength range (0.3 - 5 microns), using the Hubble and Spitzer Space Telescopes. Our results show a feature-rich transmission spectrum, with absorption from Na, H2O, and CO2, as well as wavelength-dependent scattering from small-particle condensates, and a grey absorber which somewhat mutes the molecular absorption features. 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 51+30-29, 23+15-9, and 33+43-25 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. 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.
Original languageEnglish
JournalMonthly Notices of the Royal Astronomical Society
Volume500
Issue number3
Publication statusPublished - 13 Oct 2020

Keywords

  • astro-ph.EP

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