Ground-based transmission spectroscopy with VLT FORS2: evidence for faculae and clouds in the optical spectrum of the warm Saturn WASP-110b

Nikolay Nikolov, Gracjan Maciejewski, Savvas Constantinou, Nikku Madhusudhan, Jonathan J. Fortney, Barry Smalley, Aarynn L. Carter, Ernst J.W. de Mooij, Benjamin Drummond, Neale P. Gibson, Christiane Helling, Nathan Mayne, Thomas Mikal-Evans, David K. Sing, Jamie Wilson

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)

Abstract

We present a ground-based optical transmission spectrum for the warm Saturn-mass exoplanet WASP-110b from two transit observations made with the FOcal Reducer and Spectrograph on the Very Large Telescope. The spectrum covers the wavelength range from 4000-8333 Å, which is binned in 46 transit depths measured to an averaged precision of 220 parts per million (ppm) over an averaged 80 Å bin for a Vmag = 12.8 star. The measured transit depths are unaffected by a dilution from a close A-type field dwarf, which was fully resolved. The overall main characteristic of the transmission spectrum is an increasing radius with wavelength and a lack of the theoretically predicted pressure-broadened sodium and potassium absorption features for a cloud-free atmosphere. We analyze archival high-resolution optical spectroscopy and find evidence for low to moderate activity of the host star, which we take into account in the atmospheric retrieval analysis. Using the AURA retrieval code, we find that the observed transmission spectrum can be best explained by a combination of unocculted stellar faculae and a cloud deck. Transmission spectra of cloud-free and hazy atmospheres are rejected at a high confidence. With a possible cloud deck at its terminator, WASP-110b joins the increasing population of irradiated hot-Jupiter exoplanets with cloudy atmospheres observed in transmission.
Original languageEnglish
Article number88
Number of pages16
JournalAstronomical Journal
Volume162
Issue number3
Early online date3 Aug 2021
DOIs
Publication statusPublished - 1 Sept 2021

Keywords

  • Exoplanet atmospheres

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