Nikolov, N;
Sing, DK;
Fortney, JJ;
Goyal, JM;
Drummond, B;
Evans, TM;
Gibson, NP;
... Spake, JJ; + view all
(2018)
An absolute sodium abundance for a cloud-free 'hot Saturn' exoplanet.
Nature
, 557
(7706)
pp. 526-529.
10.1038/s41586-018-0101-7.
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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 exoplanets1,2,3. However, observations have revealed only the narrow cores of these features rather than the full pressure-broadened profiles4,5,6. 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 abundances7,8,9. 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 = 6.9+0.6−0.46.9-0.4+0.6, and use it as a proxy for the planet’s atmospheric metallicity relative to the solar value (Zp/Zʘ = 2.3+8.9−1.72.3-1.7+8.9). This result is consistent with the mass–metallicity trend observed for Solar System planets and exoplanets10,11,12.
| Type: | Article |
|---|---|
| Title: | An absolute sodium abundance for a cloud-free 'hot Saturn' exoplanet |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1038/s41586-018-0101-7 |
| Publisher version: | http://doi.org/10.1038/s41586-018-0101-7 |
| Language: | English |
| Additional information: | This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10052588 |
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