Simulations of Turbulent, Active and Rotating Stars
|Scientific Discipline||Stars, (magneto)-hydrodynamics, turbulence, convection, magnetism, rotation, dynamo effect|
|Principal Investigator(s)||Dr Allan Sacha Brun|
|Leading Institution||Astrophysics department, CEA-Saclay, France|
|DEISA Home Site||IDRIS|
Project summary and results
The STARS project aimed at modelling in a self-consistent and three-dimensional way the complex, time dependent and nonlinear dynamics present in the Sun and stars. In particular the project wished to understand stellar magnetic activity, that depending on the spectral type of the star considered can be cyclic (solar type stars) irregular (very low mass stars, with spectral type later than M3), or even for stars with stellar mass greater than 2 solar mass, without any activity or simply possessing a modulated signal (probably due to the presence of a fossil field in their stably stratified, radiative envelope). The mechanism thought to be at the origin of the magnetism seen in solar type stars or in low mass stars is likely to be linked to dynamo action in the upper convective layers of such stars. The simultaneous existence of convective turbulent motions (that could even possess helicity), of rotation and its associated differential rotation and shear layers in stars, favour the emergence of a small and/or large scale magnetic field through induction. For more massive stars, possessing a convective core, understanding the interaction between the dynamo generated magnetic field and the probable fossil magnetic field of their radiative envelope constitute a major challenge in stellar fluid dynamics.
To study in great details the interaction between convection, rotation and magnetic field in stars was the main scientific goal of this project.
This DEISA-DECI project has been extremely fruitful in terms of understanding the complex interplay between turbulent convection and magnetism and to appreciate how difficult it is to compute a highly nonlinear and turbulent 3-D MHD solar dynamo model at low magnetic Prandtl number. It is the first time that dynamo action in a turbulent convective sphere at low magnetic Prandtl number is achieved in the solar context.
Snapshot of the radial velocity, log of enstrophy and toroidal magnetic field in the bulk of the highly turbulent convection zone of the DEISA DECI run. Highly intermittent convection and magnetic fields are observed in this first low Pm simulation of the solar convective envelope. We note the high degree of vorticity present in the downflows.