Potassium Detected in Hot Jupiter WASP-17b's Atmosphere

Potassium detection in the clear atmosphere of a hot-Jupiter: WASP-17b transmission spectroscopy

Authors:

Sedaghasti et al

Abstract:

We present FORS2 (attached to ESO's Very Large Telescope) observations of the exoplanet WASP-17b during its primary transit, for the purpose of differential spectrophotometry analysis. We use the instrument in its Mask eXchange Unit (MXU) mode to simultaneously obtain low resolution spectra of the planet hosting star, as well as several reference stars in the field of view. The integration of these spectra within broadband and smaller 100\AA~bins provides us with 'white' and spectrophotometric light curves, from 5700 to 8000\AA. Through modelling the white light curve, we obtain refined bulk and transit parameters of the planet, as well as wavelength-dependent variations of the planetary radius from smaller spectral bins through which the transmission spectrum is obtained. The inference of transit parameters, as well as the noise statistics, is performed using a Gaussian Process model. We achieve a typical precision in the transit depth of a few hundred parts per million from various transit light curves. From the transmission spectra we rule out a flat spectrum at >3σ and detect marginal presence of the pressure-broadened sodium wings. Furthermore, we detect the wing of the potassium absorption line in the upper atmosphere of the planet with 3σ confidence, both facts pointing to a relatively shallow temperature gradient of the atmosphere. These conclusions are mostly consistent with previous studies of this exo-atmosphere, although previous potassium measurements have been inconclusive.

A Cloudiness Index for Transiting hot Jupiters Based on the Sodium and Potassium Lines

A Cloudiness Index for Transiting Exoplanets Based on the Sodium and Potassium Lines: Tentative Evidence for Hotter Atmospheres Being Less Cloudy at Visible Wavelengths

Authors:

Heng et al

Abstract:

We present a dimensionless index that quantifies the degree of cloudiness of the atmosphere of a transiting exoplanet. Our cloudiness index is based on measuring the transit radii associated with the line center and wing of the sodium or potassium line. In deriving this index, we revisited the algebraic formulae for inferring the isothermal pressure scale height from transit measurements. We demonstrate that the formulae of Lecavelier et al. and Benneke & Seager are identical: the former is inferring the temperature while assuming a value for the mean molecular mass and the latter is inferring the mean molecular mass while assuming a value for the temperature. More importantly, these formulae cannot be used to distinguish between cloudy and cloudfree atmospheres. We derive values of our cloudiness index for a small sample of 7 hot Saturns/Jupiters taken from Sing et al. We show that WASP-17b, WASP-31b and HAT-P-1b are nearly cloudfree at visible wavelengths. We find the tentative trend that more irradiated atmospheres tend to have less clouds consisting of sub-micron-sized particles. We also derive absolute sodium and/or potassium abundances ∼102 cm−3 for WASP-17b, WASP-31b and HAT-P-1b (and upper limits for the other objects). Higher-resolution measurements of both the sodium and potassium lines, for a larger sample of exoplanetary atmospheres, are needed to confirm or refute this trend.

Potassium Detected in hot Jupiter HAT-P-1b's Atmosphere

GTC OSIRIS transiting exoplanet atmospheric survey: detection of potassium in HAT-P-1b from narrowband spectrophotometry

Authors:

Wilson et al

Abstract:

We present the detection of potassium in the atmosphere of HAT-P-1b using optical transit narrowband photometry. The results are obtained using the 10.4 m Gran Telescopio Canarias (GTC) together with the OSIRIS instrument in tunable filter imaging mode. We observed four transits, two at continuum wavelengths outside the potassium feature, at 6792 {\AA} and 8844 {\AA}, and two probing the potassium feature in the line wing at 7582.0 {\AA} and the line core at 7664.9 {\AA} using a 12 {\AA} filter width (R~650). The planet-to-star radius ratios in the continuum are found to be Rpl/R⋆ = 0.1176 ± 0.0013 at 6792 {\AA} and Rpl/R⋆ = 0.1168 ± 0.0022 at 8844 {\AA}, significantly lower than the two observations in the potassium line: Rpl/R⋆ = 0.1248 ± 0.0014 in the line wing at 7582.0 {\AA} and Rpl/R⋆ = 0.1268 ± 0.0012 in the line core at 7664.9 {\AA}. With a weighted mean of the observations outside the potassium feature Rpl/R⋆ = 0.1174 ± 0.0010, the potassium is detected as an increase in the radius ratio of {\Delta}Rpl/R⋆ = 0.0073 ± 0.0017 at 7582.0 {\AA} and {\Delta}Rpl/R⋆ = 0.0094 ± 0.0016 at 7664.9 {\AA} (a significance of 4.3 and 6.1 σ respectively). We hypothesise that the strong detection of potassium is caused by a large scale height, which can be explained by a high-temperature at the base of the upper atmosphere. A lower mean molecular mass caused by the dissociation of molecular hydrogen into atomic hydrogen by the EUV flux from the host star may also partly explain the amplitude of our detection.