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Simulations of Turbulent, Active and Rotating Suns and Stars

Final Report Summary - STARS2 (Simulations of Turbulent, Active and Rotating Suns and Stars)

Stars can be seen as modern physics laboratories from which fundamental physical processes as diverse as atomic physics, magnetism or turbulence can be studied and understood. Being able to model accurately their structure, dynamic and evolution is thus of fundamental importance and is the subject of intense research.

The STARS2 project aims specifically at unravelling solar and stellar turbulence, magnetism and rotation by developing state of the art realistic multi-D (either 2-D or 3-D) numerical simulations.

For instance a 3-D time dependent so called « integrated model of the Sun » coupling nonlinearly, thermally, mechanically and magnetically the radiative interior to the convective envelope has been developped. For the first time we can study in a self consistent way how the Sun as a whole (from its nuclear core up to its surface) is operating, transporting heat, energy and angular momentum and is generating and maintaining magnetic field via dynamo action. These integrated models have also allowed us to make progress on the dynamics of the tachocline, e.g. a narrow shear layer at the base of the convective envelope, thought to be at the origin of the solar large scale magnetic field and cyclic activity. These integrated models have further allowed us to model in 3-D for the first time internal waves excitation and propagation in a realistic radiative solar interior, which can subsequently guide our search of such waves in the real Sun via solar (helio) seismology. Having access to solar mean field dynamo models with cyclic activity we have started to look at how such a variability influences the global properties of the solar corona and wind of particules that may impact our planet Earth or the early evolutionary phase of a star.
Similarly, realistic models of various (spectral) type of stars have been computed within the STARS2 project. These simulations have considered in turn : How a convective core in massive stars influences the extended radiative envelope and their surface magnetism ; How the extended convective envelope of red giant stars (i.e. old Suns) rotate and transport angular momentum ; How fastly rotating young stars develop intense magnetic field that may form loops and starspots or How solar-like stars and solar analogues behave, i.e. what are the differences and common properties with respect to our Sun. Having access to fully nonlinear dynamical models of stars guide our undestanding of such fascinating and diverse objects, helping us to gain a dynamical vision of these essential components (objects) of the Universe.