Detection of Na, K, and H2O in the hazy atmosphere of WASP-6b

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 µm, and space with the Transiting Exoplanet Survey Satellite (TESS ) from 0.6-1.0 µm and the Hubble Space Telescope (HST ) Wide Field Camera 3 from 1.12-1.65 µm. 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] −0.9 ± 0.3 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.

An enhanced slope in the transmission spectrum of the hot Jupiter WASP-104b

“…To this end, it becomes necessary to understand the role of clouds/hazes in shaping the spectral signatures of transmission spectrum (e.g., Stevenson 2016;Iyer et al 2016;Heng 2016;Crossfield & Kreidberg 2017;Fu et al 2017;Gao et al 2020). Several hot Jupiters have been observed to exhibit transmission spectra dominated by a slope in the optical wavelengths, for example, HAT-P-12b (Alexoudi et al 2018;Wong et al 2020), HAT-P-18b (Kirk et al 2017), HAT-P-32b (Mallonn & Strassmeier 2016; Alam et al 2020), HATS-8b (May et al 2020), HD 189733b (Sing et al 2011;Pont et al 2013), TrES-3b (Parviainen et al 2016), WASP-6b (Jordán et al 2013;Nikolov et al 2015;Carter et al 2020), WASP-12b (Sing et al 2013), (Sedaghati et al 2017), WASP-43b (Weaver et al 2020), WASP-69b (Murgas et al 2020). Such a slope could be a potential sign of scattering processes in the planetary atmosphere, which could stem from the H2 molecules, condensates, or photochemical hazes (e.g., Lecavelier Des Etangs et al 2008;Wakeford & Sing 2015;Wakeford et al 2017b;Kitzmann & Heng 2018;Pinhas & Madhusudhan 2017;Ohno & Kawashima 2020).…”

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

“…We then proceeded with the reduction of the data by employing a custom-built, IDL-based pipeline commonly used in FORS2 analyses (e.g. Nikolov et al 2016Nikolov et al , 2018Carter et al 2020). Our initial step was to subtract the bias frames and perform flat field corrections to the raw images.…”

“…Bean et al 2010;Gibson et al 2013aGibson et al , 2017Nikolov et al 2016). The latter method has been extensively applied to a number of hot Jupiters 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(Bean et al , 2011Sedaghati et al 2015Sedaghati et al , 2016Sedaghati et al , 2017Lendl et al 2016;Nikolov et al 2016Nikolov et al , 2018Nikolov et al , 2021Gibson et al 2017;Carter et al 2020;Wilson et al 2020).…”

Transmission Spectroscopy for the Warm Sub-Neptune HD 3167c: Evidence for Molecular Absorption and a Possible High-metallicity Atmosphere

“…The Hubble Space Telescope (HST) has proven a productive facility for characterizing the atmospheres of transiting exoplanets. Observational studies released since 2019 alone include Arcangeli et al (2019), Benneke et al (2019aBenneke et al ( , 2019b, Chachan et al (2019), dos Santos et al (2019), Mikal-Evans et al (2019, Sing et al (2019), Spake et al (2019), Guo et al (2020), Wong et al (2020), Alam et al (2020), Fu et al (2020), Wakeford et al (2020), Carter et al (2020), Bruno et al (2020), Sotzen et al (2020), Carone et al (2020), Kreidberg et al (2020), and Colón et al (2020). Transmission spectroscopy measurements, made during primary transit, allow the composition of the day-night terminator atmosphere to be probed, while at other phases in the orbit when the irradiated dayside hemisphere is visible, the planetary emission can be constrained (for overviews, see Deming & Seager 2017;Deming et al 2019).…”

“…Transmission spectroscopy measurements, made during primary transit, allow the composition of the day-night terminator atmosphere to be probed, while at other phases in the orbit when the irradiated dayside hemisphere is visible, the planetary emission can be constrained (for overviews, see Deming & Seager 2017;Deming et al 2019). Most HST transmission and emission spectroscopy observations have been performed using either the Space Telescope Imaging Spectrograph (STIS) at near-UV/ optical wavelengths (e.g., Sing et al 2019;Alam et al 2020;Fu et al 2020) or Wide Field Camera 3 (WFC3) at near-infrared wavelengths (e.g., Arcangeli et al 2019;Benneke et al 2019aBenneke et al , 2019bMikal-Evans et al 2019Carter et al 2020). To date, published observations have mainly focused on hot Jupiters, which are especially favorable targets owing to their large radii and high temperatures (e.g., Sing et al 2016).…”