Atmospheric evaporation of exoplanets
Exoplanets are often found in close orbits around their host stars, exposing them to stellar irradiation several orders of magnitude higher than for any planet in our own solar system. The intense stellar irradiation, especially at UV and X-ray wavelengths, can drive substantial mass loss of the exoplanetary atmosphere. We use high-energy observations and numerical simulations to study the evolution of this evaporation. Evaporating atmospheres are observed through high-resolution optical and UV observations as well as high-energy observations.
If you are interested in exploring the catalog from our recent paper, Foster et al. 2021, and don't want to wait until the paper is published by the journal and the catalog is accessible through Vizier, you can download the catalog file here: catalog, and the readme file: Readme_Foster2021
Transmission and reflection measurements of exoplanet atmospheres
Atmospheres of exoplanets can be studied during primary transits as well as during eclipses. One either studies the filtering of starlight through the planetary atmosphere (transmission spectroscopy) or the reflection on the planetary dayside shortly before and after eclipse. We use high-resolution transit observations with PEPSI to search for certain atomic species in atmospheres, and use broadband or low-resolution eclipse measurements to search for clouds on exoplanets.
Stellar magnetic activity with and without planets
The magnetic field of stars is driven by the stellar dynamo, through a combination of rotation and convection. It causes a plethora of observable phenomena, such as starspots, flares, and the high-energy emission from the stellar corona. We study the intricate connection between stellar age, rotation, and activity. Furthermore, it is a long-standing question if close-in exoplanets can alter stellar activity patterns through processes like flare triggering or tidal interaction. We use large datasets of light curves through TESS and Kepler, as well as targeted X-ray observations of stellar samples, to determine the influence of exoplanets.
Flares are explosive events in the atmospheres of stars that are visible all over the electromagnetic spectrum. Their occurrence rates as well as their location on the surface of stars give clues about the underlying magnetic dynamo process. We study flares through space-based light curves and high-resolution spectroscopy.
Coronal mass ejections and their interaction with planets
Coronal mass ejections are well-observed for the Sun, but for stars we have to rely on observational proxies and numerical simulations. Especially M dwarfs are an active target for our numerical studies, as their coronal mass ejections may have consequences for exoplanets located in their habitable zones.
Magnetic field measurements of stars
Larger magnetic structures on the surface of stars can be studied with spectropolarimetry and through magnetic line broadening in integral light. We use both approaches to study the magnetic fields of cool and hot stars.
Simulations of stellar convection
Stellar convection is one of the key ingredients in the stellar dynamo. We conduct 3D simulations with the CO5BOLD code to study the effect of elemental abundances and other variables on stellar atmospheres.
For inquiries about thesis projects, please contact the head of the section (Prof. Dr. Katja Poppenhäger).