  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, H$\alpha$, 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.
