PhD Research & Publications

Stellar flares of active M-type stars (or M dwarfs) can affect the atmospheric chemical composition of orbiting planets. Such variations in the composition can then change the observed signal, which in turn can bias the data analysis process (retrievals). We have investigated the effects of stellar flares on the chemical composition of a tidally-locked, close-orbiting gaseous planet with an effective temperature of 800 K and considered the impact on the transmission spectra. We use a two-dimensional thermo-and photochemical kinetics model that takes into account horizontal transport due to equatorial superrotation, the latter dominating the circulation patterns of such planets.

As an affiliate of the European JWST MIRI GTO program, I helped with the analysis of WASP-107b, a puffy cool warm Jupiter, observed in transmission with the James Webb Space Telescope (JWST). By building a digital twin of it's atmosphere, we could simulate the chemical composition under different assumptions and compare this to the observed data. The retrieval analysis showed clear evidence for sulphur dioxide, which is best explained by a model that starts from a metal enriched atmosphere and is subjected to photochemistry induced by the host star. Furthermore, there was no evidence for methane, although its presence was expected based on our chemistry simulations. Several explanations were proposed, including a high C/O ratio, vertical mixing, high intrinsic temperature, or a high-altitude cloud deck, but further research is needed to confirm the origin of the missing methane.

The vast majority of planets that we have discovered, orbit main sequence (MS) stars like our Sun. Solar-type stars will eventually evolve off the main sequence and become asymptotic giant branch (AGB) stars, during which the star will increase in size, become much brigher and develop a strong stellar wind. The star's planetary system will likely be affected as the giant AGB star will induce tidal forces that can change the planetary orbits. Additionally, the extreme brightness will heat the planetary atmosphere and potentially change their chemical composition. Finally, the planet will be embedded in a strong and dense circumstellar environment. Within our research team at KU Leuven, we try to assess how the planetary atmosphere is affected by the latter through hydrodynamical modelling.