No Consistent Atmospheric Absorption Detected for the Ultra-hot Jupiter WASP-189b

We observed a partial transit of the ultra-hot Jupiter WASP-189 b with PEPSI on the LBT. We detect a highly variable transit signal in multiple atomic transitions, including H-alpha, Fe I, and Mg I. The signal is not consistent with a transiting planetary atmosphere. We suggest instead that the in-transit signal is due to an inhomogeneous stellar surface. Our observations demonstrate the lack of a highly extended atmosphere in common optical atomic tracers. Although WASP-189 is very bright, atmospheric characterization of the planet will be difficult due to the small transit depth and apparently compact atmosphere.


Average transmission spectra (left panels) and time series absorption (right panels) for the lines with detected absorption signatures. Note that the Mg I transmission spectrum is the average of all three triplet members. The vertical gray lines in the time series panels mark the transit contact points. Although there is some significant in-transit variability, no signal consistent with an extended atmosphere around the planet is detect.


Read more: Wilson et al. 2020, Research Notes of the AAS, Volume 4, Issue 4, id.53