Exoplanets and Stellar Activity

As astronomers started to use more and more precise instruments to detect planets outside our own Solar System, i.e. exoplanets, they realised that inhomogeneities and energetic events on the stellar surface disturb their measurements. These phenomena, collectively known as activity, find their origin in the magnetic field generated in the interior of the star. Stellar activity represents a serious limitation to the reliabe detection and characterisation of exoplanets, and especially those that are Earth-like because it camouflages their existence. Furthermore, magnetic activity alters the atmospheric chemistry of exoplanets, and ultimately their habitability. This is a crucial aspect to consider if the goal is to find signs of life elsewhere.

Under the general headline of stellar activity, my research interests can be summarised as follows:

  • Understanding the space environment around a star, as dictated by its magnetic field, and its impact on orbiting planets in terms of atmospheric evolution
  • Monitoring the long-term evolution of stellar magnetic fields, i.e. cycles, to both feed back dynamo theories and inform observing strategies for exoplanet transmission spectroscopy
  • Investigating numerical techniques to mitigate the effect of activity in radial velocity searches, to improve our capability at detecing a genuine planetary signal in a robust way
To perform my studies, I mainly use spectropolarimetry in visible and near-infrared domain. This technique allows us to collect light in different polarisation states and model the stellar magnetic field by means of Zeeman-Doppler imaging. The properties derived from the magnetic field maps can then be adopted to, for instance, simulate stellar winds and star-planet interactions or develop methods to filter stellar activity signals. In this context, M dwarfs (that is cool, low-mass stars) represent exquisite laboratories because they can be extremely active and for long time scales. Typical instruments I analysed data from are: ESPaDOnS and SPIRou both at Canada-France-Hawaii Telescope (Mauna Kea, Hawaii, United States), and NEO-NARVAL at Telescope Bernard-Lyot (Pic du Midi, France).