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Solar-to-supersolar sodium and oxygen absolute abundances for a ‘hot Saturn’ orbiting a metal-rich star

Nikolov, Nikolay K; Sing, David K; Spake, Jessica J; Smalley, Barry; Goyal, Jayesh M; Mikal-Evans, Thomas; Wakeford, Hannah R; Rustamkulov, Zafar; Deming, Drake; Fortney, Jonathan J; Carter, Aarynn; Gibson, Neale P; Mayne, Nathan J


Nikolay K Nikolov

David K Sing

Jessica J Spake

Jayesh M Goyal

Thomas Mikal-Evans

Hannah R Wakeford

Zafar Rustamkulov

Drake Deming

Jonathan J Fortney

Aarynn Carter

Neale P Gibson

Nathan J Mayne


We present new analysis of infrared transmission spectroscopy of the cloud-free hot-Saturn WASP-96b performed with the Hubble and Spitzer Space Telescopes (HST and Spitzer). The WASP-96b spectrum exhibits the absorption feature from water in excellent agreement with synthetic spectra computed assuming a cloud-free atmosphere. The HST-Spitzer spectrum is coupled with Very Large Telescope (VLT) optical transmission spectroscopy which reveals the full pressure-broadened profile of the sodium absorption feature and enables the derivation of absolute abundances. We confirm and correct for a spectral offset of $\Delta R_{{\rm p}}/R_{\ast }=(-4.29^{+0.31}_{-0.37})\, \times 10^{-3}$ of the VLT data relative to the HST-Spitzer spectrum. This offset can be explained by the assumed radius for the common-mode correction of the VLT spectra, which is a well-known feature of ground-based transmission spectroscopy. We find evidence for a lack of chromospheric and photometric activity of the host star which therefore make a negligible contribution to the offset. We measure abundances for Na and O that are consistent with solar to supersolar, with abundances relative to solar values of $21^{+27}_{-14}$ and $7^{+11}_{-4}$, respectively. We complement the transmission spectrum with new thermal emission constraints from Spitzer observations at 3.6 and 4.5 $\mu$m, which are best explained by the spectrum of an atmosphere with a temperature decreasing with altitude. A fit to the spectrum assuming an isothermal blackbody atmosphere constrains the dayside temperature to be Tp = 1545 ± 90 K.

Journal Article Type Article
Acceptance Date May 30, 2022
Online Publication Date Jun 7, 2022
Publication Date Aug 4, 2022
Deposit Date May 30, 2023
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Oxford University Press
Peer Reviewed Peer Reviewed
Volume 515
Issue 2
Pages 3037-3058
Keywords Space and Planetary Science, Astronomy and Astrophysics