The Fe XXII I(11.92 Å)/I(11.77 Å) Density Diagnostic Applied to the Chandra High Energy Transmission Grating Spectrum of EX Hydrae
Abstract
Using the Livermore X-ray Spectral Synthesizer, which calculates spectral models of highly charged ions based primarily on HULLAC atomic data, we investigate the temperature, density, and photoexcitation dependence of the I(11.92 Å)/I(11.77 Å) line ratio of Fe XXII. We find that this line ratio has a critical density nc~5×1013 cm-3, is approximately 0.3 at low densities and 1.5 at high densities, and is very insensitive to temperature and photoexcitation; therefore, it is a useful density diagnostic for sources like magnetic cataclysmic variables, in which the plasma densities are high and in which the efficacy of the He-like ion density diagnostic is compromised by the presence of a bright ultraviolet continuum. Applying this diagnostic to the Chandra High Energy Transmission Grating spectrum of the intermediate polar EX Hya, we find that the electron density of its Te~12 MK plasma is ne=1.0+2.0-0.5×1014 cm-3, which is orders of magnitude greater than that typically observed in the Sun or other late-type stars.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- May 2003
- DOI:
- 10.1086/375684
- arXiv:
- arXiv:astro-ph/0304080
- Bibcode:
- 2003ApJ...588L.101M
- Keywords:
-
- Atomic Processes;
- Stars: Binaries: Close;
- Stars: Individual: Constellation Name: EX Hydrae;
- Stars: Magnetic Fields;
- X-Rays: Binaries;
- Astrophysics
- E-Print:
- 11 pages including 3 encapsulated postscript figures