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Session 71 - Stellar Activity/Starspots.
Display session, Thursday, June 13
Tripp Commons,

[71.09] Modeling Magnetic Flux Emergence in HD 106225

M. J. Wills, E. E. DeLuca (SAO), D. B. Guenther (St. Mary's)

Using a ``thin flux tube'' approximation proposed by Spruit (1981), and working with a numerical simulation previously used to model solar magnetic flux dynamics, we attempt to create magnetic flux tube emergence in HD 106225, a rapidly rotating subgiant star, which has been observed to have both x-ray emission and starspots. Initial attempts, placing the stellar dynamo at the base of the convection zone, as has been done in solar modeling, were unsuccessful. Fisher, McClymont, amp; Chou (1991) show that, if the pressure scale height at the base of the convection zone is a significant fraction of the radius at that point (\Lambda/R > 0.3), the magnetic tension force increases faster than the buoyancy as the tube is stretched, and no rise occurs from a tube anchored at the base of the convection zone. However, Spruit amp; van Ballegooijen (1982a, b) prove that, for stars with sufficiently deep convection zones, it is possible to create a buoyantly stable flux tube in the convection zone itself. The stability of a given mode again depends on the value of \Lambda/R at a given radius. If \Lambda/R > 0.3, a flux tube is able to maintain null buoyancy in the convection zone proper.

Using Spruit amp; van Ballegooijen's solutions, we are able to run numerical simulations that model stable flux tubes in the convection zone. We have also been able to create the rise of a magnetic flux perturbation by placing the base of the ring at a stable convective radius with the perturbation extending to a more buoyant radius. Initial attempts have been based on a simplified model, placing a flux tube at zero latitude with no rotation. We also attempt simulations which allow for flux rise at non-zero latitudes and include Coriolis force. Using these results, we examine the implications that such a magnetic field pattern has for the stellar dynamo.

Program listing for Thursday