The Nonisothermal Stage of Magnetic Star Formation
Kunz, Matthew Walter
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https://hdl.handle.net/2142/80613
Description
Title
The Nonisothermal Stage of Magnetic Star Formation
Author(s)
Kunz, Matthew Walter
Issue Date
2009
Doctoral Committee Chair(s)
Stack, John D.
Department of Study
Physics
Discipline
Physics
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Theory
Language
eng
Abstract
We follow the formation and subsequent evolution of fragments (or cores) in magnetically-supported, self-gravitating molecular clouds in two spatial dimensions. The six-fluid (neutrals, electrons, molecular and atomic ions, positively-charged, negatively-charged, and neutral grains) physical system is governed by the radiative, nonideal magnetohydrodynamic (RMHD) equations. The magnetic flux is not assumed to be frozen in any of the charged species. Its evolution is determined by a newly-derived generalized Ohm's law, which accounts for the contributions of both elastic and inelastic collisions to ambipolar diffusion and Ohmic dissipation. The species abundances are calculated using an extensive chemical-equilibrium network. The thermal evolution of the protostellar core and its affect on the dynamics are followed by employing the grey flux-limited diffusion approximation. Realistic temperature-dependent grain opacities are used that account for a variety of grain compositions. We have augmented the publicly-available Zeus-MP code to take into consideration all these effects and have modified several of its algorithms to improve convergence, accuracy and efficiency. We present results of magnetic star formation simulations that accurately track the evolution of a protostellar fragment over eleven orders of magnitude in density, from the early ambipolar-diffusion-initiated fragmentation phase, the magnetically-supercritical dynamical collapse phase, and the magnetic decoupling stage, all the way to the nonisothermal phase, including the formation and evolution of a hydrostatic core of radius ≈ 2 AU, density ≈ 1014 cm-3, temperature ≈ 300 K, magnetic field strength ≈ 0.2 G, luminosity ∼ 10-3 L⊙ , and mass ∼ 10-2 M⊙ .
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