Non-equilibrium Ionization and FIP Effect Diagnostics

We examine the accuracy of a common FIP 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 non-equilibrium 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 non-equilibrium effects as well as temperature and density dependence must be evaluated for each line ratio used in the diagnostics.