Abstract

I will present the unambiguous detection of magnetic fields in the radiative cores of red giant stars using asteroseismology. Magnetic fields are thought to affect stars throughout their evolution. But their strength and topology inside stars, particularly in the non-convective stably stratified radiative layers, remain basically unconstrained observationally as well as theoretically. This prevents us from constructing reliable models of angular momentum and chemical element transport, which are at the heart of modern stellar evolution theory.

Magnetic fields induce shifts in the frequencies of oscillation modes and break the symmetry of dipole mode multiplets of slowly rotating stars. We detected such features and find that they closely follow the predictions of magnetic perturbations to oscillation modes that we generalized to an arbitrary field. The measured field strengths range from _{30 to} 600 kG in the vicinity of the hydrogen-burning shell, and we obtain information on the field topology.

The discovery of strong magnetic fields in the cores of red giants confirm that the transport of angular momentum in these objects can have a magnetic origin. More generally, with both rotation rate and magnetic field measurements, the core of red giants could become a privileged laboratory to study the interactions between magnetic fields and rotation in collisional plasmas.