Probing the atmosphere of WASP-69 b with low- and high-resolution transmission spectroscopy

¹ Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
e-mail: skhalafi@lsw.uni-heidelberg.de
² Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
³ Department of Physics, New York University Abu Dhabi, PO Box 129188, Abu Dhabi, UAE
⁴ Center for Astro, Particle and Planetary Physics (CAP3), New York University Abu Dhabi, PO Box 129188, Abu Dhabi, UAE
⁵ Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
⁶ Institut für Astrophysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
⁷ Centro de Astrobiología (CSIC-INTA), ESAC, Camino bajo del castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
⁸ Department of Physics, Bu-Ali Sina University, Hamedan 65178, Iran
⁹ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
¹⁰ Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
¹¹ Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
¹² Centro Astronómico Hispano-Alemán, Observatorio de Calar Alto, 04550 Gérgal, Almería, Spain
¹³ Sterrewacht Leiden, Universiteit Leiden, Postbus 9513, 2300 RA, Leiden, The Netherlands
¹⁴ Stellar Astrophysics Centre, Aarhus Universitet, Ny Munkegade 120, 8000 Aarhus C, Denmark
¹⁵ Astronomical Observatory, Institute of Theoretical Physics and Astronomy, Vilniaus universitetas, Sauletekio av. 3, 10257 Vilnius, Lithuania
¹⁶ Institut für Weltraumforschung, Österreichische Akademie der Wissenschaften, Schmiedlstrasse 6, 8042 Graz, Austria
¹⁷ Institut für Astronomie, Universität Wien, Türkenschanzstrasse 17, 1180 Wien, Austria
¹⁸ Observatoire de Genève, Université de Genève, Chemin des maillettes 51, 1290 Sauverny, Switzerland
¹⁹ European Space Research and Technology Centre, European Space Agency, Keplerlaan 1, 2201, AZ Noordwijk, The Netherlands
²⁰ Facultad de Ciencias Físicas, Departamento de Física de la Tierra y Astrof ísica & IPARCOS-UCM (Instituto de Física de Partículas y del Cosmos de laUCM), Universidad Complutense de Madrid, 28040 Madrid, Spain
²¹ Instituto de Astrofísica de Canarias, c/ Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
²² Universidad de La Laguna, Departamento de Astrofísica, 38206 La Laguna, Tenerife, Spain
²³ Institut de Ciéncies de l’Espai (CSIC-IEEC), Campus UAB, c/de Can Magrans s/n, 08193 Bellaterra, Barcelona, Spain
²⁴ Institut d’Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain
²⁵ Centro de Astrobiología (CSIC-INTA), Carretera de Ajalvir km 4, Torrejón de Ardoz, 28850 Madrid, Spain

Received: 27 April 2021
Accepted: 24 August 2021

Abstract

Consideration of both low- and high-resolution transmission spectroscopy is key for obtaining a comprehensive picture of exoplanet atmospheres. In studies of transmission spectra, the continuum information is well established with low-resolution spectra, while the shapes of individual lines are best constrained with high-resolution observations. In this work, we aim to merge high- with low-resolution transmission spectroscopy to place tighter constraints on physical parameters of the atmospheres. We present the analysis of three primary transits of WASP-69 b in the visible (VIS) channel of the CARMENES instrument and perform a combined low- and high-resolution analysis using additional data from HARPS-N, OSIRIS/GTC, and WFC3/HST already available in the literature. We investigate the Na I D₁ and D₂ doublet, Hα, the Ca II infra-red triplet (IRT), and K I λ7699 Å lines, and we monitor the stellar photometric variability by performing long-term photometric observations with the STELLA telescope. During the first CARMENES observing night, we detected the planet Na I D₂ and D₁ lines at ~7 and ~3σ significance levels, respectively. We measured a D₂/D₁ intensity ratio of 2.5 ± 0.7, which is in agreement with previous HARPS-N observations. Our modelling of WFC3 and OSIRIS data suggests strong Rayleigh scattering, solar to super-solar water abundance, and a highly muted Na feature in the atmosphere of this planet, in agreement with previous investigations of this target. We use the continuum information retrieved from the low-resolution spectroscopy as a prior to break the degeneracy between the Na abundance, reference pressure, and thermosphere temperature for the high-resolution spectroscopic analysis. We fit the Na I D₁ and D₂ lines individually and find that the posterior distributions of the model parameters agree with each other within 1σ. Our results suggest that local thermodynamic equilibrium processes can explain the observed D₂ /D₁ ratio because the presence of haze opacity mutes the absorption features.