Detection of Na, K and H$_2$O in the hazy atmosphere of WASP-6b

TL;DR

This study combines multi-instrument observations to detect sodium, potassium, and water vapor in WASP-6b's hazy atmosphere, revealing elemental abundances and the impact of stellar heterogeneity on atmospheric retrievals.

Contribution

It provides the first comprehensive multi-wavelength transmission spectrum of WASP-6b, including analysis of stellar heterogeneity effects on atmospheric composition.

Findings

Detected Na I, K I, and H₂O absorption features.

Constrained oxygen abundance to [O/H] ≈ -0.9 ± 0.3.

Haze presence affects sodium and potassium abundance estimates.

Abstract

We present new observations of the transmission spectrum of the hot Jupiter WASP-6b both from the ground with the Very Large Telescope (VLT) FOcal Reducer and Spectrograph (FORS2) from 0.45-0.83 $\mu$m, and space with the Transiting Exoplanet Survey Satellite (TESS) from 0.6-1.0 $\mu$m and the Hubble Space Telescope (HST) Wide Field Camera 3 from 1.12-1.65 $\mu$m. Archival data from the HST Space Telescope Imaging Spectrograph (STIS) and Spitzer is also reanalysed on a common Gaussian process framework, of which the STIS data show a good overall agreement with the overlapping FORS2 data. We also explore the effects of stellar heterogeneity on our observations and its resulting implications towards determining the atmospheric characteristics of WASP-6b. Independent of our assumptions for the level of stellar heterogeneity we detect Na I, K I and H$_2$O absorption features and constrain the elemental oxygen abundance to a value of [O/H] $\simeq -0.9\pm0.3$ relative to solar. In contrast, we find that the stellar heterogeneity correction can have significant effects on the retrieved distributions of the [Na/H] and [K/H] abundances, primarily through its degeneracy with the sloping optical opacity of scattering haze species within the atmosphere. Our results also show that despite this presence of haze, WASP-6b remains a favourable object for future atmospheric characterisation with upcoming missions such as the James Webb Space Telescope.