Slowly rotating stars with reversed butterfly diagrams: how to explain these dynamos?

November 14, 2019

We analysed a simulation of a solar-like star that is rotating slowly enough to revert its differential rotation profile from the solar-like one with a fast equator and slow poles into one with a slow equator and fast poles. In this simulation, the butterfly diagram, describing migration of the mean azimuthal magnetic field as function of time, also reversed from solar-like equatorward migration into a poleward one. Numerical solutions of this kind are unusual, but very interesting, as the Sun itself may approach such a regime, when it ages and slows down...

Slowly rotating stars with reversed butterfly diagrams: how to explain these dynamos?

We analysed a simulation of a solar-like star that is rotating slowly enough to revert its differential rotation profile from the solar-like one with a fast equator and slow poles into one with a slow equator and fast poles. In this simulation, the butterfly diagram, describing migration of the mean azimuthal magnetic field as function of time, also reversed from solar-like equatorward migration into a poleward one. Numerical solutions of this kind are unusual, but very interesting, as the Sun itself may approach such a regime, when it ages and slows down.

We used the test-field method to calculate the turbulent transport coefficients and found out that the turbulent alpha effect plays a major role in the generation of the mean toroidal magnetic field, therefore the dynamo is not an α Ω dynamo (where turbulence generates the poloidal magnetic field and differential rotation the toroidal magnetic field) as in the case of the Sun, but rather an α2 or α2Ω dynamo, where the differential rotation plays a marginal role.

 
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