2008/06/20 by F P Keenan, F. P. Keenan, D. B. Jess +9 · 1 citation
Physics and Astronomy · #Astronomy #Astrophysics #Atomic and Molecular Physics #Electron #Electron density #Emission spectrum #Extreme ultraviolet #Laser #Line (geometry) #Optics #Physics #Radiative transfer #Solar and Space Plasma Dynamics #Solar flare #Spectral line #Spectrograph #Stellar, planetary, and galactic studies #Telescope #Ultraviolet #Wavelength #astro-ph
paper · pdf · doi:10.1111/j.1365-2966.2008.13615.x
11 pages, 10 figures, MNRAS in press
arxiv created 2008/06/20 · openalex publication_date 2008/07/31 · arxiv updated 2009/12/01 · openalex created_date 2020/11/23 · openalex updated_date 2026/08/05
Fully relativistic calculations of radiative rates and electron impact excitation cross-sections for Fe x are used to derive theoretical emission-line ratios involving transitions in the 174–366 Å wavelength range. A comparison of these with solar active region observations obtained during the 1989 and 1995 flights of the Solar Extreme-ultraviolet Research Telescope and Spectrograph (SERTS) reveals generally very good agreement between theory and experiment. Several Fe x emission features are detected for the first time in SERTS spectra, while the 3s23p52P3/2--3s23p4(1S)3d 2D3/2 transition at 195.32 Å is identified for the first time (to our knowledge) in an astronomical source. The most useful Fe x electron density (Ne) diagnostic line ratios are assessed to be 175.27/174.53 and 175.27/177.24, which both involve lines close in wavelength and free from blends, vary by factors of 13 between Ne= 108 and 1011cm−3, and yet show little temperature sensitivity. Should these lines not be available, then the 257.25/345.74 ratio may be employed to determine Ne, although this requires an accurate evaluation of the instrument intensity calibration over a relatively large wavelength range. However, if the weak 324.73 Å line of Fe x is reliably detected, the use of 324.73/345.74 or 257.25/324.73 is recommended over 257.25/345.74. Electron densities deduced from 175.27/174.53 and 175.27/177.24 for the stars Procyon and α Cen, using observations from the Extreme-Ultraviolet Explorer (EUVE) satellite, are found to be consistent and in agreement with the values of Ne determined from other diagnostic ratios in the EUVE spectra. A comparison of several theoretical extreme-ultraviolet Fe x line ratios with experimental values for a θ-pinch, for which the plasma parameters have been independently determined, reveals reasonable agreement between theory and observation, providing some independent support for the accuracy of the adopted atomic data.