Transport of angular momentum and chemical elements by the MRI dynamo in stellar radiative zones

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Original abstract

The question of angular momentum transport by magnetic fields has recently been revived by the detection of magnetic fields in the deep interior of red giant stars. We aim at characterizing the efficiency of the transport of angular momentum and chemical elements in a stellar radiative zone subject to the magneto-rotational instability, in situations where hydrodynamical instabilities are not triggered. We use a large set of zero-net flux shearing-box simulations modelling a portion of a stellar radiative zone located close to the equatorial region. The shear is imposed in the direction of gravity, mimicking a radial differential rotation and rotation is perpendicular to gravity. We aim at establishing scaling laws between the transport efficiency and key parameters such as stratification and rotation. We obtain simulations where the MRI is triggered on the self-consistently built longitudinal field and then produces a state of self-sustained turbulence that we associate with dynamo action. We find that in the parameter range explored, both rotation and stable stratification strongly affect the vertical transport of angular momentum which is always dominated by the Maxwell stress component. In a similar way, we find that the transport of chemical composition is even more strongly affected by the stratification but less severely by rotation. Scaling laws are established and tentative extrapolations to stellar values are discussed. Transport by the stratified MRI dynamo is very promising to reconcile stellar evolution models and asteroseismic inversions of internal rotation rates of stars.

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• Official / arXiv page
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