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You searched for +publisher:"University of Colorado" +contributor:("Bradley W Hindman"). Showing records 1 – 2 of 2 total matches.

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University of Colorado

1. Featherstone, Nicholas Andrew. Exploring Convection and Dynamos in the Cores and Envelopes of Stars.

Degree: PhD, Astrophysical & Planetary Sciences, 2011, University of Colorado

We present theoretical studies in two complementary areas dealing with convection, rotation, and dynamos in A-type stars, and with local helioseismology in the Sun. Our studies begin with the main-sequence A stars (stars of about 2 solar masses) that possess a radiative envelope overlying a convective core. Using 3-D simulations with the Anelastic Spherical Harmonic (ASH) code to study full spherical domains, we examine the effects of a primordial magnetic field on the dynamo action realized in the turbulent core. Dynamo activity realized in the presence of such a field is significantly more efficient than in its absence, yielding magnetic energies that are roughly tenfold those of the kinetic energy associated with the convective motions. Both convective motions and magnetic fields assume a decidedly global-scale topology in this regime, with convective downdrafts from one side of the core streaming freely across the rotation axis, advecting and stretching magnetic fields across distant portions of the core in the process. We examine the topology of these strong magnetic fields and aspects of their generation in this super-equipartition dynamo. We next develop a 3-D inversion method for helioseismic measurements of horizontal flows obtained using ring-diagram analysis. Helioseismology uses the broad range of acoustic oscillations observed at the solar surface to study properties deep within the Sun. Our inversion method (called ARRDI) incorporates measurements of the wavefield made at multiple horizontal resolutions to discern the subsurface structure of horizontal flows within the star. We adopt a regularized least squares (RLS) approach for these inversions and develop a novel iterative extension to the RLS scheme wherein the flow field across the entire solar disk may be efficiently recovered. We have calculated the set of 3-D sensitivity kernels necessary for the application of our inversion technique to MDI data. We explore the horizontal- and depth-averaging properties of these sensitivity kernels, and find they differ substantially between measurements made at different horizontal resolutions. After characterizing the errors and averaging properties of our inversion algorithm, we examine the subsurface flows around sunspots. We find that sunspots possess outflows which extend to a depth of 10 Mm. These outflows possess a noticeable two-component structure, characterized by a near-surface moat outflow and another deeper outflow at 5 Mm. Our 3-D inversion procedure should be very useful in interpreting the vast helioseismic data sets now becoming available. Advisors/Committee Members: Juri Toomre, Bradley W Hindman, Allan Sacha Brun.

Subjects/Keywords: Convection; Dynamo Theory; Helioseismology; Astrophysics and Astronomy

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Featherstone, N. A. (2011). Exploring Convection and Dynamos in the Cores and Envelopes of Stars. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/astr_gradetds/5

Chicago Manual of Style (16th Edition):

Featherstone, Nicholas Andrew. “Exploring Convection and Dynamos in the Cores and Envelopes of Stars.” 2011. Doctoral Dissertation, University of Colorado. Accessed March 03, 2021. https://scholar.colorado.edu/astr_gradetds/5.

MLA Handbook (7th Edition):

Featherstone, Nicholas Andrew. “Exploring Convection and Dynamos in the Cores and Envelopes of Stars.” 2011. Web. 03 Mar 2021.

Vancouver:

Featherstone NA. Exploring Convection and Dynamos in the Cores and Envelopes of Stars. [Internet] [Doctoral dissertation]. University of Colorado; 2011. [cited 2021 Mar 03]. Available from: https://scholar.colorado.edu/astr_gradetds/5.

Council of Science Editors:

Featherstone NA. Exploring Convection and Dynamos in the Cores and Envelopes of Stars. [Doctoral Dissertation]. University of Colorado; 2011. Available from: https://scholar.colorado.edu/astr_gradetds/5


University of Colorado

2. Augustson, Kyle C. Convection and Dynamo Action in Massive Stars.

Degree: PhD, Astrophysical & Planetary Sciences, 2013, University of Colorado

Contact between numerical simulations and observations of stellar magnetism is sought, with an emphasis on those stars that are the most readily observed and those that may have magnetic activity cycles: the Sun, F-type, and B-type stars. Two approaches are taken in studying stellar dynamos and dynamics, utilizing three-dimensional MHD simulations run on massively parallel supercomputers with the full spherical geometry and employing a new compressible code in the spherical wedge geometry. A 3D MHD simulation of the solar dynamo that utilizes the Anelastic Spherical Harmonic (ASH) code is presented. This simulation self-consistently exhibits four prominent aspects of solar magnetism: activity cycles, polarity cycles, the equatorward field migration, and grand minima. The ASH framework and this simulation’s ability to capture many aspects of the solar dynamo represent a first step toward a more complete model of the Sun’s global-scale magnetic activity and its cycles. The dynamics and dynamos of F-type stars are studied through global-scale ASH simulations, with significant contact made between the observed differential rotation and magnetic cycle periods of these stars and those achieved in the simulations. Separately, ASH simulations of core convection in the massive B-type stars show that generation of superequipartition magnetic fields with peak strengths above 1 MG is possible within their cores, which has implications for the evolution of these stars as well as for the properties of their remnants. The internal waves excited by overshooting convection and rotation in these stars radiative exteriors are assessed for their asteroseismic signatures. The results of 3D compressive MHD simulations of the solar near-surface shear layer with the Compressible Spherical Segment (CSS) code are shown, with such layers arising in the coupled dynamics of ASH and CSS as well as in a more rapidly rotating, thin convective envelope of an F-type star. Advisors/Committee Members: Juri Toomre, Bradley W. Hindman, Mark S. Miesch, Mark P. Rast, Jeffrey B. Weiss.

Subjects/Keywords: Dynamo Theory; Fluid Dynamics; Stellar Convection; Stellar Magnetism; Astrophysics and Astronomy; Physical Processes; Stars, Interstellar Medium and the Galaxy

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Augustson, K. C. (2013). Convection and Dynamo Action in Massive Stars. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/astr_gradetds/26

Chicago Manual of Style (16th Edition):

Augustson, Kyle C. “Convection and Dynamo Action in Massive Stars.” 2013. Doctoral Dissertation, University of Colorado. Accessed March 03, 2021. https://scholar.colorado.edu/astr_gradetds/26.

MLA Handbook (7th Edition):

Augustson, Kyle C. “Convection and Dynamo Action in Massive Stars.” 2013. Web. 03 Mar 2021.

Vancouver:

Augustson KC. Convection and Dynamo Action in Massive Stars. [Internet] [Doctoral dissertation]. University of Colorado; 2013. [cited 2021 Mar 03]. Available from: https://scholar.colorado.edu/astr_gradetds/26.

Council of Science Editors:

Augustson KC. Convection and Dynamo Action in Massive Stars. [Doctoral Dissertation]. University of Colorado; 2013. Available from: https://scholar.colorado.edu/astr_gradetds/26

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