Detecting H₂O with CRIRES+: WASP-20b

Abstract

Context. Infrared spectroscopy over a wide spectral range and at the highest resolving powers (R>70 000) has proved to be one of the leading technique to unveil the atmospheric composition of dozens of exoplanets. The recently upgraded spectrograph CRIRES instrument at the VLT (CRIRES+) was operative for a first Science Verification in September 2021 and its new capabilities in atmospheric characterisation were ready to be tested. Aims. We analysed transmission spectra of the Hot Saturn WASP-20b in the K-band (1981-2394 nm) acquired with CRIRES+, aiming to detect the signature of H 2 O and CO. Methods. We used Principal Component Analysis to remove the dominant time-dependent contaminating sources such as telluric bands and the stellar spectrum and we extracted the planet spectrum by cross-correlating observations with 1D and 3D synthetic spectra, with no circulation included. Results. We present the tentative detection of molecular absorption from water-vapour at S/N equal to 4.2 and 4.7 by using only-H 2 O 1D and 3D models, respectively. The peak of the CCF occurred at the same rest-frame velocity for both model types (V rest =−1 ± 1 km s −1 ), and at the same projected planet orbital velocity but with different error bands (1D model: K P =131 +18 −29 km s −1 ; 3D: K P =131 +23 −39 km s −1 ). Our results are in agreement with the one expected in literature (132.9 ± 2.7 km s −1 ).Conclusions. Although sub-optimal observational conditions and issues with pipeline in calibrating and reducing our raw data set, we obtained the first tentative detection of water in the atmosphere of WASP-20b. We suggest a deeper analysis and additional observations to confirm our results and unveil the presence of CO.

Optimising spectroscopic observations of transiting exoplanets

“…High-resolution ground-based results have been consistently obtained for over a decade (e.g. Redfield et al 2008;Snellen et al 2008Snellen et al , 2010Bean et al 2010;Astudillo-Defru & Rojo 2013;Di Gloria et al 2015;Allart et al 2017;Brogi et al 2018;Diamond-Lowe et al 2018;Merritt et al 2021;Nikolov et al 2021;Maimone et al 2022;Maguire et al 2023), and more recently, even in collaboration with space-based results (e.g. Boucher et al 2023;Spyratos et al 2023).…”