Engin Keles, Daniel Kitzmann, Matthias Mallonn, Xanthippi Alexoudi, Luca Fossati, Lorenzo Pino, Julia Victoria Seidel, Thorsten A. Caroll, M. Steffen, Ilya Ilyin, Katja Poppenhäger, Klaus G. Strassmeier, Carolina von Essen, Valerio Nascimbeni, Jake D. Turner

• High spectral resolution transmission spectroscopy is a powerful tool to characterize exoplanet atmospheres. Especially for hot Jupiters, this technique is highly relevant, due to their high-altitude absorption, e.g. from resonant sodium (Na i) and potassium (K i) lines. We resolve the atmospheric K i absorption on HD189733b with the aim to compare the resolved K i line and previously obtained high-resolution Na i-D line observations with synthetic transmission spectra. The line profiles suggest atmospheric processes leading to a line broadening of the order of ∼10 km/s for the Na i-D lines and only a few km/s for the K i line. The investigation hints that either the atmosphere of HD189733b lacks a significant amount of K i or the alkali lines probe different atmospheric regions with different temperature, which could explain the differences we see in the resolved absorption lines.