Differential Rotation in Magnetized and Non-magnetized Stars

Abstract

Effects of magnetic field on stellar differential rotation are studied by comparing magnetohydrodynamic (MHD) models and their hydrodynamic (HD) counterparts in the broad range of rotation rate and in varying initial rotation profile. Fully-compressible MHD simulations of rotating penetrative convection are performed in a full-spherical shell geometry. Critical conditions for the transition of the differential rotation between faster equator (solar-type) and slower equator (anti-solar type) are explored with focusing on the "Rossby number ($\mathrm{Ro}$)" and the "convective Rossby number (${\mathrm{Ro}}_{\mathrm{conv}}$)". It is confirmed that the transition is more gradual and the critical value for it is higher in the MHD model than the HD model in the view of the ${\mathrm{Ro}}_{\mathrm{conv}}$-dependence. The rotation profile shows, as observed in earlier studies, the bistability near the transition in the HD model, while it disappears when allowing the growth of magnetic fields except for the model with taking anti-solar type solution as the initial condition. We find that the transition occurs at $\mathrm{Ro}\simeq 1$ both in the MHD and HD models independently of the hysteresis. Not only the critical value, the sharpness of the transition is also similar between the two models in the view of the $\mathrm{Ro}$-dependence. The influences of the dynamo-generated magnetic field and/or the hysteresis on convective motion are reflected in the $\mathrm{Ro}$. This would be the reason why the transition is unified in the view of the $\mathrm{Ro}$-dependence. We finally discuss the $\mathrm{Ro}$-dependence of magnetic dynamo activities with emphasis on its possible relation to the kinetic helicity profile.

16 pages, 12 figures, Accepted for publication in ApJ

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Cited by in corpus (4)

• Solar-like to Antisolar Differential Rotation: A Geometric Interpretation
• Hunting for anti-solar differentially rotating stars using the Rossby number -- An application to the Kepler field
• Convective Differential Rotation in Stars and Planets I: Theory
• Convective Differential Rotation in Stars and Planets II: Observational and Numerical Tests