Nonequilibrium ionization and first ionization potential effect diagnostics

We examine the accuracy of a common first ionization potential effect diagn ostic, the ratio of Ne VI to Mg VI lines in the solar transition region. Si nce the two ions have quite similar contribution functions near their maxim a in equilibrium, the ratio of these two ions is often taken to be the abun dance ratio of Ne and Mg. First we compute nonequilibrium ionization effect s on the ratio f(Ne+5)/f(Mg+5) of ion fractions for a variety of simple flo ws through the transition region. Calculating the spectral line ratios for a few examples, we then show that nonequilibrium effects as well as tempera ture and density dependence must be evaluated for each line ratio used in t he diagnostics.