Maxwellian Averaged Collision Strengths Research Articles

κ distribution of carbon II doublet in the solar transition region

For accurate spectral diagnostics of the solar plasma in the transition region, the averaged collision strength of the κdistribution of electron energies is discussed for non-Maxwellian distribution, and the Maxwellian averaged collision strengths and the non-Maxwellian averaged collision strengths for κ = 2, 3 and 5 from 104.4 to 106.0 K are calculated for Carbon II doublet in the transition region. Results are in agreement with those from the CHIANTI database, and the main error comes from the approximation of the collision strength. This calculation will be significant for spectral diagnostics of the solar plasma for non-Maxwellian distribution of the electron energies.

Temperature diagnostics for carbon IV ion by using a collision model in the solar transition region

For spectral diagnostics of temperature in the solar transition region, by using a semi-classical method, we calculate the collision strengths for the dipole transition of carbon IV 2S1/2-2P1/2 and 2S1/2-2P3/2, and we discuss the Maxwellian-averaged collision strengths for a wide temperature region. Then, based on the Maxwellian-averaged collision strengths, we discuss the spectral diagnostic of temperature in the solar transition region and obtain the temperature T = 1.7 × 105 K for the carbon IV ion in that region, which is in good agreement with the predicted temperature range of 1.0 × 105 K to 2.0 × 105 K. This calculation will be significant for spectral diagnostics in the solar transition region.

Fine-structure collision strengths and line ratios for [Ne v] in infrared and optical sources

New collisions’ strengths for the mid-infrared (mid-IR) and optical transitions in Ne v are presented. Breit–Pauli-R-Matrix calculations for electron impact excitation are carried out with fully resolved near-threshold resonances at very low energies. In particular, the fine-structure lines at 14 and 24 μm due to transitions among the ground state levels 1s22s22p3 3P0, 1, 2, and the optical/near-ultraviolet lines at 2973, 3346 and 3426 Å transitions among the 3P0, 1, 2, 1D2, 1S0 levels are described. Maxwellian-averaged collision strengths are tabulated for all forbidden transitions within the ground configuration. While some significant differences are found for both the far infrared and the optical transitions compared to previous results, computed line emissivity ratios are in good agreement, but change rapidly in the low temperature range Te < 10 000 K. An analysis of the 14/24 μm ratio in low-energy-density (LED) plasma conditions reveals considerable variation; the effective rate coefficient may be dominated by the very low energy behaviour rather than the Maxwellian-averaged collision strengths. Computed values suggest a possible solution to the anomalous mid-IR ratios found to be lower than theoretical limits observed from planetary nebulae and Seyfert galaxies. While such LED conditions may be present in infrared sources, they might be inconsistent with photoionization equilibrium models.

Computation of Non-Maxwellian Electron Excitation Rates for Ions of Astrophysical Interest: Fe xv – A Test Case

Dzifcakova previously developed a method for calculating the influence of nonthermal electron-velocity distributions on the intensities of spectral lines (Solar Phys.234, 243, 2006; In: Lacoste, H., Ouwehand, L. (eds.) SOHO-17. 10 Years of SOHO and Beyond, SP-617, ESA, Noordwijk, 89, 2006). Here, we study this method in detail for the test case: Fe xv. It involves fitting a parametric form to the electron-excitation data in the CHIANTI atomic database. We assess the reliability of these fits by comparing them with the source atomic data, both Upsilons (Maxwellian-averaged collision strengths) and the original collision strengths. An accuracy for the method of better than 15% is deduced for all transitions, with a much higher accuracy than this for the strong electric-dipole transitions. A κ-distribution, which has an increased number of electrons in the high-energy tail of the distribution, is considered as an example. The shape of the κ-distribution affects the electron-excitation rate and thus the relative intensities of the spectral lines. Since the shape of the electron distribution function also influences the ionization balance of Fe, both effects change the final intensities of the lines. Synthetic spectra for Fe xv and Fe xvi in the wavelength range 50 – 80 A are presented for a κ-distribution and compared with solar observations.

CHIANTI—An Atomic Database for Emission Lines. VI. Proton Rates and Other Improvements

The CHIANTI atomic database contains atomic energy levels, wavelengths, radiative transition probabilities, and electron excitation data for a large number of ions of astrophysical interest. Version 4 has been released, and proton excitation data are now included, principally for ground configuration levels that are close in energy. The fitting procedure for excitation data, both electrons and protons, has been extended to allow nine-point spline fits in addition to the previous five-point spline fits. This allows higher quality fits to data from close-coupling calculations where resonances can lead to significant structure in the Maxwellian-averaged collision strengths. The effects of photoexcitation and stimulated emission by a blackbody radiation field in a spherical geometry on the level balance equations of the CHIANTI ions can now be studied following modifications to the CHIANTI software. With the addition of H I, He I, and N I, the first neutral species have been added to CHIANTI. Many updates to existing ion data sets are described, while several new ions have been added to the database, including Ar IV, Fe VI, and Ni XXI. The two-photon continuum is now included in the spectral synthesis routines, and a new code for calculating the relativistic free-free continuum has been added. The treatment of the free-bound continuum has also been updated.

Relativistic and resonance effects in electron impact excitation ofFe5+

Relativistic and resonance effects in electron impact excitation of Fe5+ are investigated using four sets of close-coupling calculations with the R-matrix method. The different eigenfunction expansions for the N-electron target ion consist of eight LS terms, 19 fine structure levels, dominated by the ground configuration 3d3, and 34 LS terms (80 fine structure levels) dominated by additional configurations 3d24s and 3d24p. Relativistic effects are considered in two ways: a full intermediate coupling 19-level Breit-Pauli (BP) approximation, and using the term-coupling coefficients for the target levels. Unlike the lower ionization stages of Fe, it is necessary to consider explicitly the fine structure in the target in order to delineate precisely the positions of autoionizing resonances and detailed resonance structures. Otherwise, the relativistic effects are small, as indicated by the Maxwellian averaged collision strengths from the different approximations. It is found that the presence of particular bound-channel resonances, corresponding to (N + 1)-electron correlation functions in the close-coupling expansion for the (e- + ion) system, has a marked effect on the near-threshold cross sections. General implications of this work are discussed. As these resonances represent real physical features they should not be treated as pseudo-resonances. It is shown that many resonant features are well reproduced by the chosen (N + 1)-electron basis set of correlation functions in the smaller eight-term LS and 19-level BP calculations, as verified by comparison with the 34-term calculation. The present collision strengths, with large resonance structures, differ considerably from earlier calculations without resonances.

A Review of Electron Impact Collisional Excitation Data for the Oxygen-Like Isoelectronic Sequence

Published data on electron impact cross sections for ions of the oxygen-like isoelectronic sequence from 1953 to the present are reviewed. All transitions for which tabulated data are available are listed and classified according to source, type, method, and year of publication. Where possible, Maxwellian averaged collision strengths are computed at a standard set of atomic charge scaled electron temperatures. Compatible effective collision strengths are assembled into data sets that allow interpolation in charge and electron temperature and are suitable for excited level population studies.

Rate coefficients for the excitation of infrared and ultraviolet lines in C II, N III, and O IV

view Abstract Citations (145) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Rate Coefficients for the Excitation of Infrared and Ultraviolet Lines in C ii, N iii, and O IV Blum, Robert D. ; Pradhan, Anil K. Abstract New and improved collision strengths and Maxwellian-averaged rate coefficients for temperatures between 1000 and 40,000 K are presented for all the prominent transitions in the spectra of C II, N III, and O IV. The collision strengths show extensive autoionization structures that are delineated in detail and which enhance the rate coefficients for several transitions by a considerable amount. Maxwellian-averaged collision strengths are calculated for all possible fine-structure transitions along the states included in the eigenfunction expansion of the target ion. All calculations are carried out in the close-coupling approximation using the R-matrix method as adapted for the Opacity Project. Publication: The Astrophysical Journal Supplement Series Pub Date: May 1992 DOI: 10.1086/191670 Bibcode: 1992ApJS...80..425B Keywords: Astronomical Spectroscopy; Carbon; Emission Spectra; Infrared Spectra; Molecular Excitation; Ultraviolet Spectra; Electron Impact; Electron Transitions; Ground State; Nitrogen; Oxygen; Astrophysics; ATOMIC PROCESSES full text sources ADS | data products SIMBAD (1)

Improved excitation rate coefficients for the N = 2 and N = 3 levels of CA XIX and Fe XXV including fine structure

Reently calculated collision strengths, including relativistic and resonance effects, are employed to compute Maxwellian averaged collision strengths for 78 transitions involving states of principal quantum numbers 2-1 and 3-1 in Ca XIX and Fe XXV. These rate parameters are tabulated at temperatures of interest in astrophysical and labortory plasmas with radiation in the hard X-ray wavelength range. For some transitions, significant differences are found with the earlier calculations of Pradhan, Norcross, and Hummer (1981).