Nonequilibrium Ionization and First Ionization Potential Effect Diagnostics

Abstract

We examine the accuracy of a common first ionization potential effect diagnostic, the ratio of Ne VI to Mg VI lines in the solar transition region. Since the two ions have quite similar contribution functions near their maxima in equilibrium, the ratio of these two ions is often taken to be the abundance ratio of Ne and Mg. First we compute nonequilibrium ionization effects on the ratio f(Ne+5)/f(Mg+5) of ion fractions for a variety of simple flows through the transition region. Calculating the spectral line ratios for a few examples, we then show that nonequilibrium effects as well as temperature and density dependence must be evaluated for each line ratio used in the diagnostics.