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 s (Na※ I) and 2.8 s (Mg※ I). We did not detect the following species: Ti※ I, Cr※ I, Ni※ I, TiO, VO, and ZrO. We impose the following 1 s 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.