Solar-to-supersolar sodium and oxygen absolute abundances for a 'hot Saturn' orbiting a metal-rich star. Issue 2 (7th June 2022)

• Record Type: Journal Article
• Authors: 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
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 515:Issue 2(2022)
• Page Start: 3037
• Page End: 3058
• Publication Date: 2022-06-07
• Subjects: techniques: spectroscopic -- planets and satellites: composition -- planets and satellites: individual: WASP-96b -- planets and satellites: atmospheres -- stars: abundances -- stars: individual: WASP-96; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stac1530
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: 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 T p = 1545 ± 90 K.