Detecting H2O with CRIRES+: WASP-20b

Astronomy and Astrophysics, vol. 667, pp. A106

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 techniques to unveil the atmospheric composition of dozens of exoplanets. The recently upgraded spectrograph CRIRES instrument at the Very Large Telescope (CRIRES+) was operative for a first science verification in September 2021, and its new capabilities in atmospheric characterization were ready to be tested. Aims. We analyzed transmission spectra of the hot Saturn WASP-20b in the K band (1981–2394 nm) that were acquired with CRIRES+ with the aim to detect the signature of H2O and CO. Methods. We used a principal component analysis to remove dominant time-dependent contaminating sources such as telluric bands and the stellar spectrum. We extracted the planet spectrum by cross-correlating observations with 1D and 3D synthetic spectra, without circulation. Results. We present the tentative detection of molecular absorption from water vapor at a signal-to-noise ratio equal to 4.2 and 4.7 by using only H2O 1D and 3D models, respectively. The peak of the cross-correlation function occurred at the same rest-frame velocity for both model types (Vrest = −1 ± 1 km s−1 ) and at the same projected orbital velocity of the planet, but with different error bands (1D model: Kp = 131 −29+18 k ms −1; 3D: Kp = 131 −39+23 k ms −1). Our results agree with the result expected in the literature (132.9 ± 2.7 km −1). Conclusions. Although the observational conditions were not ideal and we had problems with the 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.

Authors 8

1. M. C. Maimone

   Centre National de la Recherche Scientifique · European Southern Observatory · Université Côte d'Azur · Observatoire de la Côte d’Azur

   Affiliation as printed

   European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany

   Université Côte-d’Azur, Observatoire de la Côte d’Azur, CNRS, Lagrange, CS 34229 Nice, France

   Université Côte-d'Azur, Observatoire de la Côte d'Azur, CNRS, Lagrange, CS 34229 Nice, France

2. Matteo Brogi

   University of Warwick · Osservatorio Astrofisico di Torino

   Affiliation as printed

   Centre for Exoplanets and Habitability, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK

   Department of Physics, University of Warwick, Coventry CV4 7AL, UK

   INAF-Osservatorio Astrofísico di Torino, Via Osservatorio 20, 10025 Pino Torinese, Italy

3. A. Chiavassa

   Centre National de la Recherche Scientifique · Université Côte d'Azur · Max Planck Institute for Astrophysics · Observatoire de la Côte d’Azur

   Affiliation as printed

   Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Straße 1, 85741 Garching, Germany

   Université Côte-d’Azur, Observatoire de la Côte d’Azur, CNRS, Lagrange, CS 34229 Nice, France

   Université Côte-d'Azur, Observatoire de la Côte d'Azur, CNRS, Lagrange, CS 34229 Nice, France

4. Mario E. van den Ancker

   European Southern Observatory

   Affiliation as printed

   European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany

5. Carlo Felice Manara

   European Southern Observatory

   Affiliation as printed

   European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany

6. Jérémy Leconte

   Centre National de la Recherche Scientifique · Laboratoire d'Astrophysique de Bordeaux

   Affiliation as printed

   Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France

   Laboratoire d'astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France

7. Siddharth Gandhi Aachen Leiden Observatory

   Leiden University · University of Warwick · Leiden Observatory

   Affiliation as printed

   Centre for Exoplanets and Habitability, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK

   Department of Physics, University of Warwick, Coventry CV4 7AL, UK

   Leiden Observatory, Leiden University, Postbus 9513, 2300 RA Leiden, The Netherlands

8. William Pluriel

   University of Geneva

   Affiliation as printed

   Département d’astronomie de l’Université de Genève, Chemin Pegasi 51, 1290 Versoix, Switzerland

   Département d'astronomie de l'Université de Genève, Chemin Pegasi 51, 1290 Versoix, Switzerland