Nikolov, N, Sing, DK, Fortney, JJ, Goyal, JM, Drummond, B, Evans, TM, Gibson, NP, De Mooij, EJW, Rustamkulov, Z, Wakeford, HR, Smalley, B ORCID: 0000-0002-3456-087X, Burgasser, AJ, Hellier, C ORCID: 0000-0002-3439-1439, Helling, C, Mayne, NJ, Madhusudhan, N, Kataria, T, Baines, J, Carter, AL, Ballester, GE, Barstow, JK, McCleery, J and Spake, JJ (2018) An absolute sodium abundance for a cloud-free 'hot Saturn' exoplanet. Nature, 557 (7706). 526 - 529. ISSN 1476-4687

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Abstract

Broad absorption signatures from alkali metals, such as the sodium (Na I) and potassium (K I) resonance doublets, have long been predicted in the optical atmospheric spectra of cloud-free irradiated gas giant exoplanets1-3. However, observations have revealed only the narrow cores of these features rather than the full pressure-broadened profiles4-6. Cloud and haze opacity at the day-night planetary terminator are considered to be responsible for obscuring the absorption-line wings, which hinders constraints on absolute atmospheric abundances7-9. Here we report an optical transmission spectrum for the 'hot Saturn' exoplanet WASP-96b obtained with the Very Large Telescope, which exhibits the complete pressure-broadened profile of the sodium absorption feature. The spectrum is in excellent agreement with cloud-free, solar-abundance models assuming chemical equilibrium. We are able to measure a precise, absolute sodium abundance of logεNa = [Formula: see text], and use it as a proxy for the planet's atmospheric metallicity relative to the solar value (Zp/Zʘ = [Formula: see text]). This result is consistent with the mass-metallicity trend observed for Solar System planets and exoplanets10-12.

Item Type: Article
Additional Information: This is the accepted author manuscript (AAM). The final published version (version of record) is available online via Nature Publishing Group at https://doi.org/10.1038/s41586-018-0101-7. Please refer to any applicable terms of use of the publisher.
Subjects: Q Science > QB Astronomy
Q Science > QB Astronomy > QB460 Astrophysics
Q Science > QB Astronomy > QB600 Planets. Planetology
Divisions: Faculty of Natural Sciences > School of Chemical and Physical Sciences
Related URLs:
Depositing User: Symplectic
Date Deposited: 16 Jul 2018 10:26
Last Modified: 16 Jul 2018 10:26
URI: http://eprints.keele.ac.uk/id/eprint/5117

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