The characterization of exoplanets plays a major role in understanding their
origin and evolution. To date, more than 5000 exoplanets have been detected
and this number increases daily. A suitable method to study exoplanet
properties offers transmission spectroscopy, where a small fraction of the
starlight is absorbed by atoms and molecules in the atmosphere of the
exoplanet during the planetary transit, putting a fingerprint on top of the
stellar spectrum.  Especially hot giant planets, so-called hot and ultra-hot
Jupiters, are suitable targets for transmission spectroscopy, due to their
large scale heights and short orbital periods.
In this talk, I will give a basic introduction to exoplanets and focus on the
method of high-resolution transmission spectroscopy. I will show what has been
done at the AIP in recent years regarding the characterization of gas giant
planet atmospheres with datasets observed at the Large-Binocular-Telescope
with the PEPSI instrument. In particular, I will show how atmospheric
absorption lines can be used to constrain atmospheric wind properties of
exoplanets.

In this talk, we will review some aspects of the stellar magnetism and in particular what numerical simulations tell us about the physical processes underlying the observations. In cool Sun-like stars, a convective dynamo is thought to be responsible for the presence and evolution of magnetic fields. One important aspect of stellar dynamos is the possible presence of magnetic cycles, whose characteristics depend on the stellar parameters. Another question is how magnetic flux is transported from the interior to the surface to produce starspots and whether those spots play a role in the dynamo process. In hotter and more massive stars, the manifestations of a magnetic field are drastically different. Only 5 to 10% of those stars seem to exhibit a strong dipolar magnetic field while most of the other stars are thought to possess a weak complex field. The reason for the existence of this magnetic dichotomy could be linked to the development of magnetic instabilities. We will show in this talk that numerical simulations may help us tackle several of the above key questions about stellar magnetism.