The Fe XXII I(11.92 A)/I(11.77 A) Density Diagnostic

Using the Livermore X-ray Spectral Synthesizer, which calculates spectral models of highly charged ions based on HULLAC atomic data, we investigate the temperature, density, and photoexcitation dependence of the I(11.92 A)/I(11.77 A) line ratio of Fe XXII. Applied to the Chandra HETG spectrum of the intermediate polar EX Hya, we find that the electron density of its T_e ~ 12 MK plasma is log n_e (cm^-3) = 14.3^{+0.7}_{-0.5}, orders of magnitude greater than that observed in the Sun or other late-type stars.