2020MNRAS.498.1023K

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.