Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: First Application of the Fe XVII I(17.10 A)/I(17.05 A) Line Ratio to
  Constrain the Plasma Density of a Cosmic X-ray Source   We show that the Fe XVII I(17.10 A)/I(17.05 A) 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 A)/I(17.05 A) line ratio can be explained if the plasma density n_e >
3x10^{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 T_bb > 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%. This constraint and the observed X-ray flux
requires a density n > 2x10^{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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The categories of this paper are: atom-ph
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The categories of this paper are: stat
14
The categories of this paper are: math-ph
9
The categories of this paper are: nlin
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The categories of this paper are: patt-sol
10
The categories of this paper are: q-bio
12
The categories of this paper are: nucl-th
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The categories of this paper are: acc-phys
3
The categories of this paper are: physics
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The categories of this paper are: ao-sci
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The categories of this paper are: hep-lat
13
The categories of this paper are: quant-ph
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The categories of this paper are: chem-ph
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The categories of this paper are: alg-geom
18
The categories of this paper are: econ
35
The categories of this paper are: mtrl-th