Convection and Dynamo Action in Massive Stars

Author
Abstract
<p>Contact between numerical simulations and observations of stellar magnetism is sought,\&nbsp;<span style="line-height: 1.6em;">with an emphasis on those stars that are the most readily observed and those that may have\&nbsp;</span><span style="line-height: 1.6em;">magnetic activity cycles: the Sun, F-type, and B-type stars. Two approaches are taken in\&nbsp;</span><span style="line-height: 1.6em;">studying stellar dynamos and dynamics, utilizing three-dimensional MHD simulations run\&nbsp;</span><span style="line-height: 1.6em;">on massively parallel supercomputers with the full spherical geometry and employing a new\&nbsp;</span><span style="line-height: 1.6em;">compressible code in the spherical wedge geometry. A 3D MHD simulation of the solar\&nbsp;</span><span style="line-height: 1.6em;">dynamo that utilizes the Anelastic Spherical Harmonic (ASH) code is presented. This simulation\&nbsp;</span><span style="line-height: 1.6em;">self-consistently exhibits four prominent aspects of solar magnetism: activity cycles,\&nbsp;</span><span style="line-height: 1.6em;">polarity cycles, the equatorward field migration, and grandminima. The ASH framework and\&nbsp;</span><span style="line-height: 1.6em;">this simulation\textquoterights ability to capture many aspects of the solar dynamo represent a first step\&nbsp;</span><span style="line-height: 1.6em;">toward a more complete model of the Sun\textquoterights global-scale magnetic activity and its cycles. The\&nbsp;</span><span style="line-height: 1.6em;">dynamics and dynamos of F-type stars are studied through global-scale ASH simulations,\&nbsp;</span><span style="line-height: 1.6em;">with significant contact made between the observed differential rotation and magnetic cycle\&nbsp;</span><span style="line-height: 1.6em;">periods of these stars and those achieved in the simulations. Separately, ASH simulations\&nbsp;</span><span style="line-height: 1.6em;">of core convection in the massive B-type stars show that generation of superequipartition\&nbsp;</span><span style="line-height: 1.6em;">magnetic fields with peak strengths above 1 MG is possible within their cores, which has\&nbsp;</span><span style="line-height: 1.6em;">implications for the evolution of these stars as well as for the properties of their remnants.\&nbsp;</span><span style="line-height: 1.6em;">The internal waves excited by overshooting convection and rotation in these stars radiative\&nbsp;</span><span style="line-height: 1.6em;">exteriors are assessed for their asteroseismic signatures. The results of 3D compressive MHD\&nbsp;</span><span style="line-height: 1.6em;">simulations of the solar near-surface shear layer with the Compressible Spherical Segment\&nbsp;</span><span style="line-height: 1.6em;">(CSS) code are shown, with such layers arising in the coupled dynamics of ASH and CSS as\&nbsp;</span><span style="line-height: 1.6em;">well as in a more rapidly rotating, thin convective envelope of an F-type star.</span></p>
Year of Publication
2013
Degree
Ph.D.
Number of Pages
502
Date Published
2014-01
University
University of Colorado Boulder
City
Boulder
Advisors - JILA Fellows
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