Detecting H₂O with CRIRES+: WASP-20b

Infrared spectroscopy over a wide spectral range and at the highest resolving powers (R>70 000) has proved to be one of leading technique unveil atmospheric composition dozens exoplanets. The recently upgraded spectrograph CRIRES instrument VLT (CRIRES+) was operative for first Science Verification in September 2021 its new capabilities characterisation were ready tested. We analysed transmission spectra Hot Saturn WASP-20b K-band (1981-2394 nm) acquired with CRIRES+, aiming detecting signature H2O CO. used Principal Component Analysis remove dominant time-dependent contaminating sources such as telluric bands stellar spectrum we extracted planet by cross-correlating observations 1D 3D synthetic spectra, no circulation included. present tentative detection molecular absorption from water-vapour S/N equal 4.2 4.7 using only-H2O models, respectively. peak CCF occurred same rest-frame velocity both model types (Vrest=-1 $\pm$ 1 kms$^{-1}$), projected orbital but different error (1D model: KP=131$^{+18}_{-29}$ kms$^{-1}$; 3D: KP=131$^{+23}_{-39}$ kms$^{-1}$). Our results are agreement expected literature (132.9 2.7 Although sub-optimal observational conditions issues pipeline calibrating reducing our raw data set, obtained water atmosphere WASP-20b. suggest deeper analysis additional confirm presence