2001/06/28 by Christopher W. Mauche, D. A. Liedahl, Duane A. Liedahl +2 · 2 citations
Physics and Astronomy · #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Atomic and Molecular Physics #Atomic physics #Excited state #Flux (metallurgy) #Ion #Line (geometry) #Materials science #Nuclear physics #Photoexcitation #Physics #Plasma #Population #Spectral line #Stars #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/323067
13 pages including 1 table and 4 encapsulated postscript figures; LaTeX format, uses aastex.cls; accepted on 2001 June 27 for publication in The Astrophysical Journal
arxiv created 2001/06/28 · openalex publication_date 2001/10/20 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/06
We show that the Fe XVII I (17.10 Å)/ I (17.05 Å) line ratio observed in the Chandra High-Energy Transmission Grating (HETG) spectrum of the intermediate polar EX Hya 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 Å)/ I (17.05 Å) line ratio can be explained if the plasma density n e ≳ 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 T bb ≳ 55 kK. For photoexcitation to dominate the Fe XVII level-population kinetics, the relative size of the hot spot on the white dwarf surface must be f ≲ 2%. This constraint, and the observed X-ray flux, requires a density n ≳ 2 × 10 14 cm -3 for the postshock flow. Either way, then, the Chandra HETG spectrum of EX Hya requires a plasma density that is orders of magnitude greater than that observed in the Sun or other late-type stars.