LRG-BEASTS: Sodium absorption and Rayleigh scattering in the atmosphere of WASP-94A b using NTT/EFOSC2. Issue 4 (6th January 2022)

• Record Type: Journal Article
• Authors: Ahrer, E; Wheatley, P J; Kirk, J; Gandhi, S; King, G W; Louden, T
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 510:Issue 4(2022)
• Page Start: 4857
• Page End: 4871
• Publication Date: 2022-01-06
• Subjects: methods: observational -- techniques: spectroscopic -- planets and satellites: atmospheres -- planets and satellites: individual: WASP-94A b; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stab3805
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: We present an optical transmission spectrum for WASP-94A b, the first atmospheric characterization of this highly-inflated hot Jupiter. The planet has a reported radius of $1.72^{+0.06}_{-0.05}$ RJup, a mass of only $0.456^{+0.032}_{-0.036}$ MJup, and an equilibrium temperature of 1508 ± 75 K. We observed the planet transit spectroscopically with the EFOSC2 instrument on the ESO New Technology Telescope (NTT) at La Silla, Chile: the first use of NTT/EFOSC2 for transmission spectroscopy. We achieved an average transit-depth precision of 128 ppm for bin widths of ∼200 Å. This high precision was achieved in part by linking Gaussian Process hyperparameters across all wavelength bins. The resulting transmission spectrum, spanning a wavelength range of 3800–7140 Å, exhibits a sodium absorption with a significance of 4.9σ, suggesting a relatively cloud-free atmosphere. The sodium signal may be broadened, with a best-fitting width of $78_{-32}^{+67}$ Å in contrast to the instrumental resolution of 27.2 ± 0.2 Å. We also detect a steep slope in the blue end of the transmission spectrum, indicating the presence of Rayleigh scattering in the atmosphere of WASP-94A b. Retrieval models show evidence for the observed slope to be super-Rayleigh and potential causes are discussed. Finally, we find narrow absorption cores in the CaII H&K lines of WASP-94A, suggesting the star is enshrouded in gas escaping the hot Jupiter.