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| Paper: |
New Era in 3-D Modeling of Convection and Magnetic Dynamos in Stellar Envelopes and Cores |
| Volume: |
462, Progress in Solar/Stellar Physics with Helio- and Asteroseismology |
| Page: |
331 |
| Authors: |
Toomre, J.; Augustson, K. C.; Brown, B. P.; Browning, M. K.; Brun, A. S.; Featherstone, N. A.; Miesch, M. S. |
| Abstract: |
The recent advances in asteroseismology and spectropolarimetry are beginning to
provide estimates of differential rotation and magnetic structures for a
range of F and G-type stars possessing convective envelopes, and in A-type stars
with convective cores. It is essential to complement such observational work with
theoretical studies based on 3-D simulations of highly turbulent convection coupled
to rotation, shear and magnetic fields in full spherical geometries. We have so
employed the anelastic spherical harmonic (ASH) code, which deals with compressible
magnetohydrodynamics (MHD) in spherical shells, to examine the manner in which the global-scale convection
can establish differential rotation and meridional circulations under current solar rotation
rates, and these make good contact with helioseismic findings. For younger G
stars rotating 3 to 5 times faster than the current Sun, the convection establishes
ever stronger angular velocity contrasts between their fast equators
and slow poles, and these are accompanied by prominent latitudinal temperature
contrasts as well. Turning to MHD simulation of magnetic dynamo action within
these younger G stars, the resulting magnetism involves wreaths of strong
toroidal magnetic fields (up to 50 to 100 kG strengths) in the bulk of the
convection zone, typically of opposite polarity in the northern and southern
hemispheres. These fields can persist for long intervals despite being pummeled
by the fast convective downflows, but they can also
exhibit field reversals and cycles. Turning to shallower convective envelopes in
the more luminous F-type stars that range in mass from 1.2 to 1.4 solar masses and
for various rotation rates, we find that the convection can again establish
solar-like differential rotation profiles with a fast equator and slow poles,
but the opposite is achieved at the slower rotation rates. The F stars
are also capable of building strong magnetic fields, often as wreaths, through
dynamo action. We also consider dynamo action within the cores of rotating
A-type stars, finding that striking super-equipartition magnetic fields can be
built there. These families of 3-D simulations are showing that a new era of
detailed stellar modeling is becoming feasible through rapid advances in
supercomputing, and these have the potential to help interpret and possibly
even guide some of the observational efforts now under way. |
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