Linking the chemical composition of stars and exoplanets : impact of planet engulfment and transport processes
Abstract
Stars and exoplanets are formed from the same accretion disk and are expected to have the same initial chemical composition. However, once the host-star is not fully convective anymore, its surface abundance changes with time because of several processes. Firstly, internal transport processes of chemical elements such as atomic diffusion, rotation-induced mixing, or penetrative convection affect the surface abundances with different efficiencies. The abundance changes depend on the age of the host star but also on its spectral type. Secondly, the host star may also undergo accretion of rocky bodies in the system at different periods of its evolution. It can go from the accretion of small asteroids to the engulfment of planetoids, and all these events may leave a chemical signature at the surface of the star. In this presentation, we will show how we can derive the initial chemical composition of the planetary systems by modelling the host star with a realistic transport of chemical elements. Moreover, we will show that the accreted matter from planet engulfments does not remain at the surface of stars because of the same transport processes. Such accretion events also trigger additional efficient transport processes, such as the thermohaline convection, which strongly reduce the remaining signature at the surface of stars. We also show that the timing of such an event during the evolution of the host star strongly affects the amplitude of the chemical signature. The accurate modelling of transport processes in stars is crucial for the interpretation of chemical signature in this context.