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| Paper: |
Symmetry Changes of Magnetic Fields in the Sun and Other Stars |
| Volume: |
154, Cool Stars, Stellar Systems and the Sun: Tenth Cambridge Workshop |
| Page: |
1349 |
| Authors: |
Tobias, S. M. |
| Abstract: |
Much can be learned about magnetic activity in cool stars by studying in detail the behaviour of our nearest star, the Sun. The basic eleven year cycle for magnetic activity on the Sun is chaotically modulated on longer timescales and interrupted by recurrent ``grand minima''. Moreover, observations show that for the past three hundred years the Sun's toroidal magnetic field has been largely dipolar (symmetric about the equator) except when the Sun was emerging from the Maunder minimum. Here we present the results of a nonlinear dynamo model that demonstrates that chaotically modulated cycles (with grand minima) are the preferred states if the rotation rate of the star is sufficiently large. Moreover the minima can act as a switch --- with the magnetic field emerging from a minimum with a different symmetry to that with which it entered. Hence the fact that the Sun has been largely dipolar for the past three hundred years may be misleading. First of all the Sun itself may flip symmetries (and may have done so in the past). Secondly, and more importantly, the result has important implications for other cool stars, by demonstrating that stars with different rotation rates may have dipole, quadrupole or mixed symmetry and even that stars with the same rotation rates may have magnetic fields of different symmetries or fields that flip from one symmetry to another. |
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