During this project, the ASTROFLOW group worked in two directions. One part of the team developed models of winds of cool stars and studied the propagation of energetic particles through these winds. We have also modelled the propagation and ejection of bursty events, known as coronal mass ejections. Our models allow us to characterise the particle and magnetic environment surrounding exoplanets. Additionally, they can be compared to radio observations, allowing us to better understand specific systems.
The other part of the team worked on developing 3D simulations of atmospheric escape of exoplanets. The escape process occurs when stellar high-energy radiation is deposited at the lower atmosphere of the planet, heating the atmosphere, which expands and more easily evaporate.
The evaporation process however does not occur in vacuum. On the contrary, the stellar wind that surrounds the escaping atmosphere can shape and alter escape. Therefore, both parts of the team work together to provide a more realistic physical characterisation of atmospheric escape in close-in exoplanets.
The stellar wind is able to shape atmospheric escape — combining the effects of stellar winds with the orbital motion, the escaping atmosphere takes the form of a “comet-like tail”. These elongated tails can be detected in spectroscopic transits. One highlight of our modelling research was that we showed that in the presence of a planetary magnetic field, the “comet-like tail” can take a different form — escape in this case can occur through polar regions. Depending on the stellar wind property, in which the planet is embedded, our simulations revealed that a magnetised escaping atmosphere could create a “double tail structure”, in which evaporation takes place mostly through both poles of the planet, or a single tail structure, where only one pole contribute to most of the escape.
