Nonequilibrium Ionization in the Bifrost Stellar Atmosphere Code
Abstract
The chromosphere and transition region have for the last 20 years been known to be quite dynamic layers of the solar atmosphere, characterized by timescales shorter than the ionization equilibrium timescales of many of the ions dominating emission in these regions. Due to the fast changes in the properties of the atmosphere, long ionization and recombination times can lead these ions to being found far from their equilibrium temperatures. A number of the spectral lines that we observe can therefore not be expected a priori to reflect information about local quantities such as the density or temperature, and interpreting observations requires numerical modeling. Modeling the ionization balance is computationally expensive and has earlier only been done in one dimension. However, onedimensional models can primarily be used to investigate the possible importance of a physical effect, but cannot verify or disprove the importance of that effect in the fully threedimensional solar atmosphere. Here, using the atomic database package DIPER, we extend onedimensional methods and implement a solver for the rate equations of the full threedimensional problem, using the numerical code Bifrost. We present our implementation and report on a few test cases. We also report on studies of the important C IV and Fe XII ions in a semirealistic twodimensional solar atmosphere model, focusing on differences between statistical equilibrium and nonequilibrium ionization results.
 Publication:

The Astronomical Journal
 Pub Date:
 March 2013
 DOI:
 10.1088/00046256/145/3/72
 Bibcode:
 2013AJ....145...72O
 Keywords:

 atomic processes;
 magnetohydrodynamics: MHD;
 methods: numerical;
 Sun: atmosphere;
 Sun: transition region;
 techniques: spectroscopic