An atlas of resolved spectral features in the transmission spectrum of WASP-189 b with MAROON-X

¹ European Southern Observatory, Alonso de Córdova 3107, Vitacura, Región Metropolitana, Chile
² Lund Observatory, Division of Astrophysics, Department of Physics, Lund University, Box 118, 221 00 Lund, Sweden
e-mail: bibiana.prinoth@fysik.lu.se
³ Space Telescope Science Institute, Baltimore, MD 21218, USA
⁴ University of Bern, Physics Institute, Division of Space Research & Planetary Sciences, Gesellschaftsstr. 6, 3012 Bern, Switzerland
⁵ Observatoire de la Côte d’Azur, CNRS UMR 7293, BP4229, Laboratoire Lagrange, 06304 Nice Cedex 4, France
⁶ School of Mathematical and Physical Sciences, Macquarie University, Sydney, NSW 2109, Australia
⁷ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
⁸ Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
⁹ Department of Physics and Trottier Institute for Research on Exoplanets, University of Montreal, Montreal, QC, Canada
¹⁰ Department of Astronomy & Astrophysics, The University of Chicago, Chicago, IL, USA

Received: 29 December 2023
Accepted: 16 February 2024

Abstract

Exoplanets in the ultra-hot Jupiter regime provide an excellent laboratory for testing the impact of stellar irradiation on the dynamics and chemical composition of gas giant atmospheres. In this study, we observed two transits of the ultra-hot Jupiter WASP-189 b with MAROON-X/Gemini-North to probe its high-altitude atmospheric layers, using strong absorption lines. We derived posterior probability distributions for the planetary and stellar parameters by calculating the stellar spectrum behind the planet at every orbital phase during the transit. This was used to correct the Rossiter–McLaughlin imprint on the transmission spectra. Using differential transmission spectroscopy, we detect strong absorption lines of Ca⁺, Ba⁺, Na, Hα, Mg, Fe, and Fe⁺, providing an unprecedented and detailed view of the atmospheric chemical composition. Ca⁺ absorption is particularly well suited for analysis through time-resolved narrow-band spectroscopy, owing to its transition lines formed in high-altitude layers. The spectral absorption lines show no significant blueshifts that would indicate high-altitude day-to-night winds, and further analysis is needed to investigate the implications for atmospheric dynamics. These high signal-to-noise observations provide a benchmark data set for testing high-resolution retrievals and the assumptions of atmospheric models. We also simulate observations of WASP-189 b with ANDES/ELT, and show that ANDES will be highly sensitive to the individual absorption lines of a myriad of elements and molecules, including TiO and CO.