Emission lines of Fe X in active region spectra obtained with the Solar Extreme-ultraviolet Research Telescope and Spectrograph

Department of Physics, The Catholic University of America, Washington, DC 20064, USA
Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.52). 09/2008; 389(2):939 - 948. DOI: 10.1111/j.1365-2966.2008.13615.x
Source: arXiv

ABSTRACT 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 3s23p5 2P3/2--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 1011 cm−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.

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    ABSTRACT: Theoretical emission-line ratios involving FeXI transitions in the 257-407Å wavelength range are derived using fully relativistic calculations of radiative rates and electron impact excitation cross-sections. These are subsequently compared with both long wavelength channel Extreme-Ultraviolet Imaging Spectrometer (EIS) spectra from the Hinode satellite (covering 245-291Å) and first-order observations (~235-449Å) obtained by the Solar Extreme-ultraviolet Research Telescope and Spectrograph (SERTS). The 266.39, 266.60 and 276.36Å lines of FeXI are detected in two EIS spectra, confirming earlier identifications of these features, and 276.36Å is found to provide an electron density (Ne) diagnostic when ratioed against the 257.55Å transition. Agreement between theory and observation is found to be generally good for the SERTS data sets, with discrepancies normally being due to known line blends, while the 257.55Å feature is detected for the first time in SERTS spectra. The most useful FeXI electron density diagnostic is found to be the 308.54/352.67 intensity ratio, which varies by a factor of 8.4 between Ne = 108 and 1011cm-3, while showing little temperature sensitivity. However, the 349.04/352.67 ratio potentially provides a superior diagnostic, as it involves lines which are closer in wavelength, and varies by a factor of 14.7 between Ne = 108 and 1011cm-3. Unfortunately, the 349.04Å line is relatively weak, and also blended with the second-order FeX 174.52Å feature, unless the first-order instrument response is enhanced.
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    ABSTRACT: A detailed study of emission lines from Fe VII, Fe VIII, and Fe IX observed by the EUV Imaging Spectrometer on board the Hinode satellite is presented. Spectra in the ranges 170-212 angstrom and 246-292 angstrom show strongly enhanced lines from the upper solar transition region (temperatures 5.4 <= log T <= 5.9) allowing a number of new line identifications to be made. Comparisons of Fe VII lines with predictions from a new atomic model reveal new plasma diagnostics, however there are a number of disagreements between theory and observation for emission line ratios insensitive to density and temperature, suggesting improved atomic data are required. Line ratios for Fe VIII also show discrepancies with theory, with the strong lambda 185.21 and lambda 186.60 lines underestimated by 60%-80% compared to lines between 192 and 198 angstrom. A newly identified multiplet between 253.9 and 255.8 angstrom offers excellent temperature diagnostic opportunities relative to the lines between 185 and 198 angstrom, however the atomic model underestimates the strength of these lines by factors of 3-6. Two new line identifications are made for Fe IX at wavelengths 176.959 angstrom and 177.594 angstrom, while seven other lines between 186 and 200 angstrom are suggested to be due to Fe IX but for which transition identifications cannot be made. The new atomic data for Fe VII and Fe IX are demonstrated to significantly modify models for the response function of the Transition Region And Coronal Explorer 195 angstrom imaging channel, affecting temperature determinations from this channel. The data will also affect the response functions for other solar EUV imaging instruments such as SOHO/EIT, STEREO/EUVI, and the upcoming AIA instrument on the Solar Dynamics Observatory.
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    Journal of Astrophysics and Astronomy 09/2012; 33(3). DOI:10.1007/s12036-012-9151-7 · 0.50 Impact Factor

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