Transmission spectroscopy with VLT FORS2: a featureless spectrum for the low-density transiting exoplanet WASP-88b

Spyratos, Petros; Nikolov, Nikolay; Southworth, John; Constantinou, Savvas; Madhusudhan, Nikku; Carter, Aarynn L; de Mooij, Ernst J W; Fortney, Jonathan J; Gibson, Neale P; Goyal, Jayesh M; Helling, Christiane; Mayne, Nathan J; Mikal-Evans, Thomas

doi:10.1093/mnras/stab1847

Transmission spectroscopy with VLT FORS2: a featureless spectrum for the low-density transiting exoplanet WASP-88b

Spyratos, Petros; Nikolov, Nikolay; Southworth, John; Constantinou, Savvas; Madhusudhan, Nikku; Carter, Aarynn L; de Mooij, Ernst J W; Fortney, Jonathan J; Gibson, Neale P; Goyal, Jayesh M; Helling, Christiane; Mayne, Nathan J; Mikal-Evans, Thomas

Authors

Petros Spyratos

Nikolay Nikolov

Dr John Taylor j.k.taylor@keele.ac.uk

Savvas Constantinou

Nikku Madhusudhan

Aarynn L Carter

Ernst J W de Mooij

Jonathan J Fortney

Neale P Gibson

Jayesh M Goyal

Christiane Helling

Nathan J Mayne

Thomas Mikal-Evans

Abstract

We present ground-based optical transmission spectroscopy of the low-density hot Jupiter WASP-88b covering the wavelength range 4413 - 8333 Å with the FORS2 spectrograph on the Very Large Telescope. The FORS2 white light curves exhibit a significant time-correlated noise which we model using a Gaussian Process and remove as a wavelength-independent component from the spectroscopic light curves. We analyse complementary photometric observations from the Transiting Exoplanet Survey Satellite and refine the system properties and ephemeris. We find a featureless transmission spectrum with increased absorption towards shorter wavelengths. We perform an atmospheric retrieval analysis with the aura code, finding tentative evidence for haze in the upper atmospheric layers and a lower likelihood for a dense cloud deck. Whilst our retrieval analysis results point toward clouds and hazes, further evidence is needed to definitively reject a clear-sky scenario.

Journal Article Type	Article
Acceptance Date	Jun 24, 2021
Online Publication Date	Jul 5, 2021
Publication Date	2021-09
Journal	Monthly Notices of the Royal Astronomical Society
Print ISSN	0035-8711
Publisher	Oxford University Press
Peer Reviewed	Peer Reviewed
Volume	506
Issue	2
Pages	2853-2870
DOI	https://doi.org/10.1093/mnras/stab1847
Keywords	methods: data analysis, techniques: spectroscopic, planets and satellites: atmospheres, stars: individual: WASP-88, planetary systems
Publisher URL	https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stab1847/6315343