Surprises in X-ray and EUV emission of cool stars as exoplanet hosts

The extreme-UV (EUV) emission of cool stars has become very fashionable in recent years, since
it is thought to be the most important driver for exoplanet evaporation. Since no observatories
have been active at this wavelength range for a long time, scaling laws are typically used to infer
the stellar EUV fluxes. However, stellar coronae and transition regions are exciting places with
interesting physics that still host some surprises. I will present results from our new catalog of
exoplanet X-ray irradiation, showing that high-energy environments can be much more extreme than
what is found for the well-studied Hot Jupiters. I will also show that some EUV assumptions made in exoplanet atmosphere studies are off by an order of magnitude, and that certain nondetections of
atmospheres are actually unsurprising when one takes into account the physics of emission lines in
the stellar corona and transition region.