Abstract
We show that the Fe XVII I(17.10 u/I(17.05 u line ratio observed in the Chandra HETG spectrum of the intermediate polar EX Hydrae is significantly smaller than that observed in the Sun or other late-type stars. Using the Livermore X-ray Spectral Synthesizer, which calculates spectral models of highly charged ions based on HULLAC atomic data, we find that the observed I(17.10 u/I(17.05 u line ratio can be explained if the plasma density ne > 3 × 10 14 cm −3 . However, if photoexcitation is included in the level population kinetics, the line ratio can be explained for any density if the photoexcitation temperature Tbb > 55 kK. For photoexcitation to dominate the Fe XVII level population kinetics, the relative size of the hotspot on the white dwarf surface must be f 2 × 10 14 cm −3 for the post-shock flow. Either way, then, the Chandra HETG spectrum of EX Hya requires a plasma density which is orders of magnitude greater than that observed in the Sun or other late-type stars.
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