Computer Science – Numerical Analysis
Scientific paper
Apr 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...442..726m&link_type=abstract
Astrophysical Journal (ISSN 0004-637X), vol. 442, no. 2, Part 1, p. 726-735
Computer Science
Numerical Analysis
61
Accretion Disks, Algorithms, Ambipolar Diffusion, Astronomical Models, Gravitational Collapse, Magnetohydrodynamics, Molecular Clouds, Numerical Analysis, Protostars, Applications Programs (Computers), Computerized Simulation, Magnetohydrodynamic Stability, Program Verification (Computers), Shock Waves
Scientific paper
Magnetic fields tied to ions can diffuse through mostly neutral gas: this occurs in protostellar disks and in the cores of molecular clouds. We describe an algorithm that includes ambipolar diffusion in the astrophysical magnetohydrodynamics code ZEUS. We use the approximations that both electrons and ions have equal and constant temperature, that the ion inertia is negligible, and that the ion density is proportional to a power of the neutral density. Our algorithm is fully explicit, and treats the magnetic field using constrained transport and the method of characteristics. We test the algorithm by computing the gravitational collapse of a magnetically supported slab, and by comparing the computed solution for an oblique C-shock to a semi-analytic solution that we have derived. We then compute the developement of the magnetorotational instability described by Balbus and Hawley in a magnetized accretion disk, including the effects of ambipolar diffusion. Our computation agrees with the published linear analysis of how diffusion prevents instability, and it allows us to describe the nonlinear development of the instability when the diffusion is important but not dominant. We find that ambipolar diffusion indeed creates the sharp structures by Brandenburg and Zweibel.
Konigl Arieh
Mac Low Mordecai-Mark
Norman Michael L.
Wardle Mark
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