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arXiv · 2209.11506

Detecting H$_2$O with CRIRES+: the case of WASP-20b

M. C. Maimone·M. Brogi·A. Chiavassa·M. E. van den Ancker·C. F. Manara·J. Leconte·S. Gandhi·W. Pluriel
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Abstract

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. We analysed transmission spectra of the Hot Saturn WASP-20b in the K-band (1981-2394 nm) acquired with CRIRES+, aiming at detecting the signature of H2O and CO. 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. We present the tentative detection of molecular absorption from water-vapour at S/N equal to 4.2 and 4.7 by using only-H2O 1D and 3D models, respectively. The peak of the CCF occurred at the same rest-frame velocity for both model types (Vrest=-1 $\pm$ 1 kms$^{-1}$), and at the same projected planet orbital velocity but with different error bands (1D model: KP=131$^{+18}_{-29}$ kms$^{-1}$; 3D: KP=131$^{+23}_{-39}$ kms$^{-1}$). Our results are in agreement with the one expected in literature (132.9 $\pm$ 2.7 kms$^{-1}$). 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.

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M. C. Maimone, M. Brogi, A. Chiavassa, M. E. van den Ancker, C. F. Manara, J. Leconte, S. Gandhi, W. Pluriel. 2022-09-23. Detecting H$_2$O with CRIRES+: the case of WASP-20b. https://doi.org/10.1051/0004-6361%2F202244383

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