Potassium detection in the clear atmosphere of a hot-Jupiter

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 100Å bins provides us with 'white' and spectrophotometric light curves, from 5700 to 8000Å. 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 3-σ 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.

ACCESS: a featureless optical transmission spectrum for WASP-19b from Magellan/IMACS

“…One of the key features of Magellan/IMACS is its large field of view (FOV) for the f {2 camera (27 1ˆ2 7 1 ), which allows for observations of several comparison stars in order to correct for common time-series variations. This is in contrast with other instruments, such as VLT/FORS2 (Sedaghati et al 2015b(Sedaghati et al , 2016Nikolov et al 2016;Sedaghati et al 2017;Gibson et al 2017), or Gemini/GMOS (Huitson et al 2017;Stevenson et al 2014;Gibson et al 2013a,b), whose relatively smaller FOVs (" 7 1ˆ71 and 2 1ˆ21 , respectively) typically only allow the observations of a single comparison star. The availability of multiple comparison stars makes it easier to detect and confrim features in the data, including spotcrossing events, which are known to occur during WASP-19b transits (see, e.g., Tregloan-Reed et al 2013;Mancini et al 2013;Huitson et al 2013) and which could bias our measurements if not accounted for.…”

ACCESS: A Visual to Near-infrared Spectrum of the Hot Jupiter WASP-43b with Evidence of H2O, but No Evidence of Na or K

“…Following Sedaghati et al (2016), we divided the detrended WLC obtained in the polynomial detrending method by its best-fit model to produce a common-mode correction (CMC) residual. We then divided that residual through the binned light curves to remove wavelength independent variations.…”

The atmosphere of WASP-17b: Optical high-resolution transmission spectroscopy

“…The source of the difference between them could be in RV component correction and in the different approach in measurement of the signal. We additionally calculate the absorption signal presented in the low-resolution transmission spectrum of WASP-17b by Sing et al (2016) as well as the upper limit on the non-detection of sodium in the transmission spectrum obtained by Sedaghati et al (2016). The results are also shown in Table 5.…”