Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS)

Abstract

High-resolution optical spectroscopy is a powerful tool to characterise exoplanetary atmospheres from the ground. The sodium D lines, with their large cross sections, are especially suited to studying the upper layers of atmospheres in this context. We report on the results from Hot Exoplanet Atmosphere Resolved with Transit Spectroscopy survey (HEARTS), a spectroscopic survey of exoplanet atmospheres, performing a comparative study of hot gas giants to determine the effects of stellar irradiation. In this second installation of the series, we highlight the detection of neutral sodium on the ultra-hot giant WASP-76b. We observed three transits of the planet using the High-Accuracy Radial-velocity Planet Searcher (HARPS) high-resolution spectrograph at the European Southern Observatory (ESO) 3.6 m telescope and collected 175 spectra of WASP-76. We repeatedly detect the absorption signature of neutral sodium in the planet atmosphere (0.371 ± 0.034%; 10.75σ in a 0.75 Å passband). The sodium lines have a Gaussian profile with full width at half maximum (FWHM) of 27.6 ± 2.8 km s−1. This is significantly broader than the line spread function of HARPS (2.7 km s−1). We surmise that the observed broadening could trace the super-rotation in the upper atmosphere of this ultra-hot gas giant.

HST/STIS transmission spectrum of the ultra-hot Jupiter WASP-76 b confirms the presence of sodium in its atmosphere

“…To illustrate this difference, we compare the WASP-76 b measurements to HD 189733b. The high-resolution sodium absorption strength of WASP-76 b and HD 189733b is very similar (Seidel et al 2019;Wyttenbach et al 2015). However, our low-resolution sodium absorption for WASP-76 b in this work is one order of magnitude stronger than the low-resolution sodium absorption of HD 189733b .…”

“…Initially, the spectra were divided into eight and thirteen wavelength bins for the blue and red gratings, respectively, and the R P /R S were computed for each bin. After Seidel et al (2019)'s work, we recomputed the transmission spectrum in the same way, but choosing three narrow bands around sodium, specifically 20 Å wide, centered at 5892.9 Å. The specific values for the wavelength bins across the whole spectrum can be seen in Table 4, along with the scatter and LDCs used for each bin.…”

Wind of change: retrieving exoplanet atmospheric winds from high-resolution spectroscopy

“…For hot Jupiters, a plethora of sodium detections have been confirmed, starting with Charbonneau et al (2002) in low resolution and Snellen et al (2008); Redfield et al (2008) up to more recent high resolution observations (e. g. Louden & Wheatley (2015); Ridden-Harper et al (2016); Wyttenbach et al (2015Wyttenbach et al ( , 2017; Casasayas- Barris et al (2017); Jensen et al (2018); Khalafinejad et al (2018); Seidel et al (2019)).…”

“…These high-resolution sodium detections show significantly broader lines than a static model of the atmosphere including pressure and temperature broadening would suggest. In the case of WASP 76b, the detected sodium doublet is ten times broader than the instrument response function (Seidel et al 2019). Both WASP 49b and HD 189733b show similar broad features (Wyttenbach et al 2017;Casasayas-Barris et al 2017).…”

Detection of Fe I and Fe II in the atmosphere of MASCARA-2b using a cross-correlation method

“…Additionally Cauley et al (2019) detected in this planet H β and Mg i triplet. These atmospheric species have also been detected in the cooler UHJs WASP-18b (Arcangeli et al 2018), WASP-33b (von Essen et al 2018), WASP-12b (Jensen et al 2012), WASP-76b (Seidel et al 2019) and MASCARA-2b (Casasayas-Barris et al 2018.…”