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

Petros Spyratos, Nikolay Nikolov, John Southworth, 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

Research output: Contribution to journalArticlepeer-review


We present ground-based optical transmission spectroscopy of the low-density hot Jupiter WASP-88b covering the wavelength range of 4413−8333  Å with the FOcal Reducer Spectrograph (FORS2) on the Very Large Telescope. The FORS2 white light curves exhibit a significant time-correlated noise that 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. While our retrieval analysis results point towards clouds and hazes, further evidence is needed to definitively reject a clear-sky scenario.
Original languageEnglish
Pages (from-to)2853-2870
Number of pages18
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Early online date5 Jul 2021
Publication statusPublished - 1 Sept 2021


  • Methods: data analysis
  • Techniques: spectroscopic,
  • Planets and satellites: atmospheres
  • Stars: individual: WASP-88
  • Planetary systems


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