Eigenvalue Method for NEI Unit in FLASH Code. (arXiv:1902.10715v1 [astro-ph.IM])
<a href="http://arxiv.org/find/astro-ph/1/au:+Zhang_G/0/1/0/all/0/1">Gao-Yuan Zhang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Foster_A/0/1/0/all/0/1">Adam Foster</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Smith_R/0/1/0/all/0/1">Randall Smith</a>
We describe an improved nonequilibrium ionization (NEI) method that we have
developed as an optional module for the FLASH magnetohydrodynamic simulation
code. The method employs an eigenvalue approach rather than the earlier
iterative ordinary differential equation approach to solve the stiff
differential equations involved in NEI calculations. The new code also allows
the atomic data to be easily updated from the AtomDB database. We compare both
the updated atomic data and the methods separately. The new atomic data are
shown to make a significant difference in some circumstances, although the
general trends remain the same. Additionally, the new method also allows
simultaneous calculation of the nonequilibrium radiative cooling, which is not
included in the original method. The eigenvalue method improves the calculation
efficiency overall with no loss of accuracy. We explore some common ways to
present the NEI state with a sample simulation and find that using the average
ionic charge difference from the equilibrium tends to be the clearest method.
We describe an improved nonequilibrium ionization (NEI) method that we have
developed as an optional module for the FLASH magnetohydrodynamic simulation
code. The method employs an eigenvalue approach rather than the earlier
iterative ordinary differential equation approach to solve the stiff
differential equations involved in NEI calculations. The new code also allows
the atomic data to be easily updated from the AtomDB database. We compare both
the updated atomic data and the methods separately. The new atomic data are
shown to make a significant difference in some circumstances, although the
general trends remain the same. Additionally, the new method also allows
simultaneous calculation of the nonequilibrium radiative cooling, which is not
included in the original method. The eigenvalue method improves the calculation
efficiency overall with no loss of accuracy. We explore some common ways to
present the NEI state with a sample simulation and find that using the average
ionic charge difference from the equilibrium tends to be the clearest method.
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