My group conducts research into several aspects of star-exoplanet systems. We use observational data from space telescopes at wavelengths from X-rays to the infrared, as well as ground-based optical data.
Transits of exoplanets in front of their host stars are our prime tool to investigate the composition of exoplanetary atmospheres. The transit depths at different wavelengths give us clues about atomic species and densities at different altitudes in the atmosphere. However, the star is not a constant “background candle”; stellar magnetic activity can cause short-tern and long-term changes in the stellar spectrum, which we need to understand and characterize to extract the exoplanetary features correctly.
Stars with an outer convective zone like the Sun produce strong, highly structured magnetic fields through a magnetic dynamo process. These magnetic fields cause star spots, flares, coronal mass ejections, and are the cause for the hot outer layers of stars, the chromosphere and corona. To understand the heating processes and sudden energy release by magnetic flares, we use X-ray observations of stellar coronae. These processes can also have a strong influence on planets in close orbits around their host stars, because high-energy irradiation is the main driver for atmospheric evaporation.
Young stars and protoplanetary disks
Planets form in the disks surrounding young stellar objects. The inner parts of such disks are not accessible to spatially resolved observations yet, we can however study the processes of the inner disk using near- and mid-infrared observations. At those wavelengths, changes in the disk are what dominates the brightness variations of the star-disk system. I am part of the YSOVAR project to study young stellar objects, planet formation, and accretion with data from the Spitzer space telescope.
Habitability of exoplanets
Planets around other stars often experience very different space weather conditions than our rather tepid Earth. Especially in systems where the host star is a red dwarf and the habitable zone is close to the star, the magnetic activity of the star can influence the chances for life to develop. We have shown that in such systems the atmosphere of habitable-zone planets may get completely stripped away.