ESPRESSO high-resolution transmission spectroscopy of WASP-76 b

Abstract

Aims. We report on ESPRESSO high-resolution transmission spectroscopic observations of two primary transits of the highly irradiated, ultra-hot Jupiter-sized planet, WASP-76b. We investigated the presence of several key atomic and molecular features of interest that may reveal the atmospheric properties of the planet. Methods. We extracted two transmission spectra of WASP-76b with R ≈ 140 000 using a procedure that allowed us to process the full ESPRESSO wavelength range (3800–7880 Å) simultaneously. We observed that at a high signal-to-noise ratio, the continuum of ESPRESSO spectra shows ‘wiggles’, which are likely caused by an interference pattern outside the spectrograph. To search for the planetary features, we visually analysed the extracted transmission spectra and cross-correlated the observations against theoretical spectra of different atomic and molecular species. Results. The following atomic features are detected: Li I, Na I, Mg I, Ca II, Mn I, K I, and Fe I. All are detected with a confidence level between 9.2 σ (Na I) and 2.8 σ (Mg I). We did not detect the following species: Ti I, Cr I, Ni I, TiO, VO, and ZrO. We impose the following 1 σ upper limits on their detectability: 60, 77, 122, 6, 8, and 8 ppm, respectively. Conclusions. We report the detection of Li I on WASP-76b for the first time. In addition, we confirm the presence of Na I and Fe I as previously reported in the literature. We show that the procedure employed in this work can detect features down to the level of ~0.1% in the transmission spectrum and ~10 ppm by means of a cross-correlation method. We discuss the presence of neutral and singly ionised features in the atmosphere of WASP-76b.

An Atomic Spectral Survey of WASP-76b: Resolving Chemical Gradients and Asymmetries

“…More information about the reduction procedure and the data can be found in the original publication where the data were presented (Ehrenreich et al 2020). This dataset has also been used in two subsequent papers, Tabernero et al (2021) and Seidel et al (2021). Tabernero et al (2021) identified individual absorption lines from Li I, Na I, Mg I, Ca II, Mn I, K I, and Fe I, and also searched for Fe I, Ti I, Cr I, Ni I, TiO, VO and ZrO using the cross correlation technique, but only detected the previously-seen Fe I signal.…”

“…This dataset has also been used in two subsequent papers, Tabernero et al (2021) and Seidel et al (2021). Tabernero et al (2021) identified individual absorption lines from Li I, Na I, Mg I, Ca II, Mn I, K I, and Fe I, and also searched for Fe I, Ti I, Cr I, Ni I, TiO, VO and ZrO using the cross correlation technique, but only detected the previously-seen Fe I signal. Seidel et al (2021) performed a concentrated analysis of the Na I doublet and found evidence for a uniform dayto-night wind, as well as a vertical wind in the upper atmosphere, which acts to significantly broaden the Na I doublet.…”

“…Before any other steps were performed, we corrected the spectra for any telluric contamination due to H 2 O and O 2 in the Earth's atmosphere using molecfit (Smette et al 2015). This method was first used by Allart et al (2017), and has subsequently been used in many studies including those on ESPRESSO data (e.g., Tabernero et al 2021;Casasayas-Barris et al 2021a). This method is successful at removing weak H 2 O lines, but fails at removing the deepest absorption lines, such as those seen in the line cores of the O 2 bands, and so even after the molecfit correction, we masked any pixels where the transmission through the atmosphere was less than 40%.…”

“…In MASCARA-2b, neutral Fe I, Na I, and Mg I, as well as ionized Ca II, Fe II, and Cr II have been identified (Casasayas-Barris et al 2019;Stangret et al 2020;Nugroho et al 2020;Hoeijmakers et al 2020b). Tabernero et al (2021) detected absorption from neutral Li I, Na I, Mg I, Fe I, K I and Mn I, and ionized Ca II in the atmosphere of WASP-76b. Planets cooler than UHJs exhibit absorption from far fewer metals (Allart et al 2020;Casasayas-Barris et al 2021a), seemingly because many elements have condensed into molecules, clouds, and hazes (e.g., Kataria et al 2016;Gao et al 2021).…”

Titanium oxide and chemical inhomogeneity in the atmosphere of the exoplanet WASP-189b

“…In recent years, similar systems have garnered significant interest within studies that use high-resolution ground-based spectrographs. These have been used to reveal a myriad of absorbing atoms in their emission and transmission spectra [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] .…”