R -MATRIX ELECTRON-IMPACT EXCITATION OF Fe ¹³⁺ AND ITS APPLICATION TO THE SOFT X-RAY AND EXTREME-ULTRAVIOLET SPECTROSCOPY OF CORONA-LIKE PLASMAS

Abstract

Accurate excitation parameters are required to interpret the ultraviolet and X-ray spectra of Fe 13+ . In this work, we use the autostructure code to describe the atomic structure of Fe 13+ . The 197 lowest-lying fine-structure levels of the 3sx 3p y 3d z (x + y + z = 3), 3s 2 4l, and 3s3p4{s, p, and d} configurations are included along with further correlation configurations: 3s3p4f , 3px 3d y 4l (x + y = 2), 3l4l 4l , and 3l3l 5l . The resultant level energies, lifetimes of excited states, and oscillator strengths of transitions between these levels are assessed by comparison with available experimental data and previous calculations. Electron-impact excitation data among these lowestlying levels are generated using the intermediate-coupling frame transformation R-matrix method. We assess the present results by comparisons with laboratory measurement for the excitation to the metastable level 3s 2 3p 2 P o 3/2 and with available close-coupling calculations for other excitations. Using these data and a collisional-radiative model, we have analyzed soft X-ray and extreme-ultraviolet spectra from space satellite observations of a stellar corona and of solar flares, as well as measurements from an electron beam ion trap. We assess the contribution from Fe 13+ emission lines in the solar and Procyon corona observations, and find and identify new lines in the X-ray region observed in the solar and Procyon coronae. The laboratory measurements also confirm that weak lines (218.177 Å and 224.354 Å) of Fe 13+ contribute to the observed intensities in solar observations. The polarization effect due to the directional monoenergetic distribution of the electron energy has been taken into account in comparison with the laboratory measurements. Electron density diagnostics for the astrophysical plasma sources have been performed using the updated data so as to investigate their sensitivity to the atomic data source.

Energy levels, radiative rates and electron impact excitation rates for transitions in Fe xiv

“…Similarly, Tayal (2008) has published energy levels, radiative rates and effective collision strengths for some transitions among the lowest 59 levels of the (1s 2 2s 2 2p 6 ) 3s 2 3p, 3s3p 2 , 3s 2 3d, 3p 3 , 3s3p3d and 3p 2 3d configurations of Fe XIV. However, in a more recent paper, Liang et al (2010) have reported A-values for a larger number of transitions among 197 levels of Fe XIV. Nevertheless, most of these workers have reported Avalues for the electric dipole (E1) transitions alone, whereas in the modelling of plasmas the corresponding results are also required for other types of transitions, namely electric quadrupole (E2), magnetic dipole (M1) and magnetic quadrupole (M2).…”

“…Nevertheless, we will discuss later the velocity/length form ratio, as this provides some assessment of the accuracy of the results. In Table 3 we compare our A-values for some of the E1 transitions, mainly among the lowest 15 levels, from GRASP1 with those of Tayal (2008) and Liang et al (2010) from the MCHF and AS codes, respectively. Also included in the table are the f-values from our GRASP1 calculations because they are indicative of the strength of a transition.…”

“…Corresponding calculations for electron impact excitation of Fe XIV are comparatively fewer, and the most notable ones are those by Dufton & Kingston (1991), Storey et al (1996Storey et al ( , 2000, Tayal (2008) and Liang et al (2010). Most of the earlier calculations for collision strengths (Ω), or more appropriately effective collision strengths (Υ), provided conflicting estimates for the physical parameters of the plasmas -see, for example, Ferguson et al (1997).…”

“…The limitation in the Tayal (2008) results was removed by Liang et al (2010), who not only performed a larger calculation among 197 levels of the 3s 2 3p, 3s3p 2 , 3s 2 3d, 3p 3 , 3s3p3d, 3p 2 3d, 3s3d 2 , 3p3d 2 , 3s 2 4 , 3s3p4s, 3s3p4p and 3s3p4d configurations, but also reported results of Υ for all transitions among these levels. To determine the atomic structure they adopted the AutoStructure (AS) code of Badnell (1997), and for collisional data the R-matrix code of Berrington et al (1995).…”

“…4 P 1/2 9.51534 9.65716 9.64323 9.59977 9.55699 9.56728 1.298-11 Liang et al (2010) from the as code Υ), especially for transitions among the fine-structure levels of a state, because resonances through the energies of degenerating levels are also taken into account. Since degeneracy among some of the levels is significant, see for example the 3s3p( 3 P)3d 4 F o 3/2,5/2,7/2,9/2 levels in Table 1, the use of this code, we believe, is more appropriate.…”