Low-frequency internal waves in magnetized rotating stellar radiation zones
I. Wave structure modification by a toroidal field
S. Mathis1,2 and N. de Brye1
Laboratoire AIM, CEA/DSM – CNRS – Université Paris Diderot,
IRFU/SAp Centre de Saclay,
e-mail: firstname.lastname@example.org, email@example.com
2 LESIA, Observatoire de Paris – CNRS – Université Paris Diderot, Place Jules Janssen, 92195 Meudon, France
Accepted: 23 September 2010
Context. The study of helioseismology, asteroseismology, and powerful ground-based instrumentation dedicated to stellar physics is developing strongly (cf. CoRoT, KEPLER, and ESPaDOnS). This generates tight constraints on the stellar internal structure and dynamical processes. In this context, it is thus necessary to go beyond the non-rotating and the non-magnetic picture of stellar interiors, particularly for large-scale transport mechanisms and waves.
Aims. We focus on low-frequency internal waves in magnetic, rotating, stably stratified stellar radiation zones. For frequencies, which can be close to the Alfvén and the inertial frequencies, we go beyond the non-magnetic and non-rotating description of wave dynamics with taking the Coriolis acceleration and the Lorentz force into account. Then, we have to couple wave dynamics with fossil magnetic fields, which must have mixed configurations (both poloidal and toroidal) to survive in stellar radiation zones.
Methods. We chose to study such coupling step by step, first with purely toroidal fields and then with purely poloidal fields, to unravel their modification by each corresponding component of a realistic mixed-field. Thus, we analytically built a complete formalism, which describes both effects of the Coriolis acceleration and of the Lorentz force in a non-perturbative way in the case of an axisymmetric toroidal field. We consider here the case where both Alfvén frequency and angular velocity are chosen to be uniform, to isolate wave properties.
Results. The different approximations possible for low-frequency internal waves in this model are examined and discussed. In this way, the traditional approximation used to describe the dynamics of low-frequency regular elliptic gravito-inertial waves in the purely hydrodynamical case is generalized to the magnetic one. The complete structure of internal waves, which become magneto-gravito-inertial waves, is then derived and compared to the non-magnetic case. The asymptotic behaviour of such waves is obtained.
Conclusions. A global study of magneto-gravito-inertial waves in stellar radiation zones is achieved in the case of an axisymmetric toroidal magnetic field. In the near future, consequences for angular momentum transport and the case of general differential rotation and azimuthal magnetic field have to be studied. Moreover, the same methodology must be applied to the case of poloidal fields, and the hyperbolic regime has to be carefully studied.
Key words: magnetohydrodynamics (MHD) / waves / methods: analytical / stars: rotation / stars: magnetic field / stars: oscillations
© ESO, 2010