Since the discovery of the first exoplanet around a solar-type star in 1995 (Mayor & Queloz 1995), a revolution is occurring in Astrophysics. More than 3000 exoplanets have been discovered and characterised around host stars of different masses and ages. The orbital architecture of these planetary systems is strongly different from the one of our Solar system. These groundbreaking discoveries change the paradigm for the understanding of the formation, the evolution and the stability of star-planet systems among which our own Solar system.
For short-period planets already discovered and those, which will be discovered and characterised by the forthcoming space missions CHEOPS (ESA) and TESS (NASA) in 2018 and PLATO (ESA) in 2024 (in which researchers of the Laboratory AIM – Astrophysics division of CEA are strongly involved), the host stars play a key role. Indeed, close planets induce in these stars complex tidal flows (such as oceanic tidal waves excited on the Earth by the combined lunar and solar tides). Their dissipation modifies the orbits of close planets and can influence the rotational dynamics of the stars (Bolmont & Mathis 2016). To understand the evolution of close star-planet systems, it is thus mandatory to build realistic ab-initio models of tidal waves and of their dissipation (e.g. Zahn 1975, Ogilvie & Lin 2004-07, Ogilvie 2013) as a function of the structural and dynamical properties of the host star. Indeed, it has been demonstrated that tidal dissipation in stars vary over several orders of magnitude as a function of the stellar mass, age, rotation and differential rotation (e.g. Mathis 2015, Mathis et al. 2016, Baruteau & Rieutord 2013, Guenel et al. 2016). Moreover, these properties of the dissipation strongly impact systems’ orbital and rotational evolution (e.g. Bolmont & Mathis 2016).
The objective of this PhD project is to model for the first time tidal waves dissipation in low-mass stars with taking into account the internal transport of angular momentum they induce (Favier et al. 2014) and magnetic fields (e.g. Wei 2016), particularly in stellar convective envelopes which are the seat of a dynamo action. The framework of this project is the European ERC project SPIRE (Stars: dynamical Processes driving tidal Interactions, Rotation and Evolution) within the Laboratory of the Dynamics of Stars and their Environment, one of the leading group in this research area, in close collaboration with the Institute of Astrophysics and Planetology (University of Toulouse), the Geneva University (Switzerland) and the Universities of Leeds and Cambridge (UK). The objective is to provide key theoretical predictions to accompany and ensure the best scientific exploitation of future space missions such as CHEOPS, TESS and PLATO.
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