The ionization equilibrium of astrophysically abundant elements

We present new calculations of ionization equilibrium fractions of 11 abundant elements (C,N,O,Ne,Mg,Si,S,Ar,Ca,Fe,Ni) as functions of temperature. We also tabulate convenient coefficients for fitting the rates of collisional ionization, radiative recombination, and dielectronic recombination. Many of the ionization rates are based on recent experimental measurements of cross sections for collisional ionization and autoionization following inner-shell excitation. These rates are used elsewhere in computations of nonequilibrium ionization, radiative cooling, radiative shock models, and plasma emission diagnostics.