Abstract
ABSTRACT 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.
Highlights
Since the first detection of a constituent in the atmosphere of a planet outside the Solar system (Charbonneau et al 2002), transmission spectroscopy has become the central tool for probing the atmospheric composition and structure of transiting exoplanets
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
We considered a variety of auxiliary systematic variables for the kernel functions of our datasets, including airmass, positional drifts, rotator angle changes, full width at half-maximum (FWHM), sky background, and ambient pressure and temperature, and determined that each transit light curve is best described by a different set of systematics
Summary
Since the first detection of a constituent in the atmosphere of a planet outside the Solar system (Charbonneau et al 2002), transmission spectroscopy has become the central tool for probing the atmospheric composition and structure of transiting exoplanets. C 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society using the FOcal Reducer Spectrograph (FORS2; Appenzeller et al 1998; Boffin et al 2016), installed on the Very Large Telescope (VLT), with success in placing constraints on the abundances of Na and K and distinguishing clear from cloudy and hazy hot-Jupiter atmospheres (Bean et al 2010, 2011; Sedaghati et al 2015, 2016, 2017; Lendl et al 2016; Nikolov et al 2016, 2018, 2021; Gibson et al 2017; Carter et al 2020; Wilson et al 2020). Observations to date reveal that most exoplanet atmospheres exhibit some level of haze/cloud in their atmosphere (Sing et al 2016) and scattering slopes have been detected across the whole continuum, from low (HATS-8b; May et al 2020) to intermediate (WASP-43b; Weaver et al 2020) surface gravities, and from warm Saturns (HAT-P-18b; Kirk et al 2017) to ultra-hot Jupiters (WASP12b; Sing et al 2016).
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