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

TL;DR

This study presents optical transmission spectroscopy of exoplanet WASP-88b, revealing a featureless spectrum with hints of haze, using VLT FORS2 data and atmospheric retrieval techniques.

Contribution

It provides the first ground-based optical transmission spectrum of WASP-88b and analyzes atmospheric composition, suggesting haze presence over clouds.

Findings

Featureless transmission spectrum observed

Tentative evidence for haze in the atmosphere

Lower likelihood of a dense cloud deck

Abstract

We present ground-based optical transmission spectroscopy of the low-density hot Jupiter WASP-88b covering the wavelength range 4413-8333 {\AA} 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.