Michael Jacobs, Ph.D. 2004

Hydrodynamic Convection in Asymptotic Giant Branch Stars

Michael Jacobs

Under the supervision of Dr. Paul Woodward

ABSTRACT

I present a work that analyzes three dimensional hydrodynamic simulations of a spherical system that nearly approximates the interior of an Asymptotic Giant Branch (AGB) star. Numerical simulations of up to 512-cubed zones are analyzed and the data reduced into both coherent visualizations and radial trends. These initial results are then further processed to sum up the global properties of the simulations. The simulations were undertaken to directly model the poorly understood process of convection in stellar bodies in the hopes that fully three dimensional numerical simulations of the hydrodynamics would provide insight that could feed back into existing convective theories.

The simulations were run on various machines in the Origin2000 array at the National Center for Supercomputing Applications (NCSA) from August 2 1999 to June 15 2002. The majority of the 350,000 service units were utilized on the v70-series simulation, results of which comprise the bulk of this work. The simulations are examined in terms of their global properties and complex internal structure whose distinctiveness from ideal spherical symmetry is striking. The simulations are further analyzed from the point of view of classical Mixing Length Theory (MLT) and its successors in order to ascertain to what degree a canonical one-dimensional parameter is able to accurately model a fully three dimensional flow on a scale that encompasses the entire giant star. I discuss how this work is interrelated with other similar studies and endeavors. I then conclude with potential ways in which the lessons learned in this study could be applied to similar problems in the future.