EFFECTIVE COLLISION STRENGTHS FOR ELECTRON-IMPACT EXCITATION OF Fe VIII
TL;DR: In this article, the B-spline Breit-Pauli R-matrix method was used to estimate the collision strength of the electron in the close-coupling approximation of Fe VIII.
Abstract: New extensive calculations are reported for electron collision strengths, rate coefficients, and transition probabilities for the astrophysically important lines of Fe VIII. The collision strengths have been calculated in the close-coupling approximation using the B-spline Breit-Pauli R-matrix method. The multiconfiguration Hartree-Fock method with term-dependent non-orthogonal orbitals is employed for an accurate representation of the target wave functions. The close-coupling expansion includes 102 fine-structure levels of Fe VIII covering all possible terms of the ground 3p 63d and singly excited 3p 53d 2, 3p 64l, 3p 53d4s, 3s3p 63d 2, and 3p 65l configurations. The present calculations are more extensive than the previous ones, leading to a total 5151 transitions between fine-structure levels. The effective collision strengths are obtained by averaging the electron collision strengths over a Maxwellian distribution of velocities and these are tabulated for all fine-structure transitions at electron temperatures in the range from 5 × 103 to 5 × 106 K. There is an overall good agreement with the previous 77-state calculations by Griffin, Pindzola, & Badnell, but significant differences are also noted for some transitions.
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TL;DR: This version of the CHIANTI database includes a large amount of new data and ions, which represent a significant improvement in the soft X-ray, EUV and UV spectral regions, which several space missions currently cover.
Abstract: We present version 8 of the CHIANTI database. This version includes a large amount of new data and ions, which represent a significant improvement in the soft X-ray, extreme UV (EUV) and UV spectral regions, which several space missions currently cover. New data for neutrals and low charge states are also added. The data are assessed, but to improve the modelling of low-temperature plasma the effective collision strengths for most of the new datasets are not spline-fitted as previously, but are retained as calculated. This required a change of the format of the CHIANTI electron excitation files. The format of the energy files has also been changed. Excitation rates between all the levels are retained for most of the new datasets, so the data can in principle be used to model high-density plasma. In addition, the method for computing the differential emission measure used in the CHIANTI software has been changed.
487 citations
TL;DR: The CHIANTI database has been updated in this paper with a large amount of new data and ions, which represent a significant improvement in the soft X-ray, EUV and UV spectral regions, which several space missions currently cover.
Abstract: We present version 8 of the CHIANTI database. This version includes a large amount of new data and ions, which represent a significant improvement in the soft X-ray, EUV and UV spectral regions, which several space missions currently cover. New data for neutrals and low charge states are also added. The data are assessed, but to improve the modelling of low-temperature plasma the effective collision strengths for most of the new datasets are not spline-fitted as previously, but are retained as calculated. This required a change of the format of the CHIANTI electron excitation files. The format of the energy files has also been changed. Excitation rates between all the levels are retained for most of the new datasets, so the data can in principle be used to model high-density plasma. In addition, the method for computing the differential emission measure used in the CHIANTI software has been changed.
306 citations
TL;DR: In this article, a review of the diagnostic methods used to measure electron densities, electron temperatures, differential emission measure (DEM), and relative chemical abundances is presented, focusing on the optically thin emission from the solar atmosphere, mostly found at UV and X-ray (XUV) wavelengths.
Abstract: X-ray and ultraviolet (UV) observations of the outer solar atmosphere have been used for many decades to measure the fundamental parameters of the solar plasma. This review focuses on the optically thin emission from the solar atmosphere, mostly found at UV and X-ray (XUV) wavelengths, and discusses some of the diagnostic methods that have been used to measure electron densities, electron temperatures, differential emission measure (DEM), and relative chemical abundances. We mainly focus on methods and results obtained from high-resolution spectroscopy, rather than broad-band imaging. However, we note that the best results are often obtained by combining imaging and spectroscopic observations. We also mainly focus the review on measurements of electron densities and temperatures obtained from single ion diagnostics, to avoid issues related to the ionisation state of the plasma. We start the review with a short historical introduction on the main XUV high-resolution spectrometers, then review the basics of optically thin emission and the main processes that affect the formation of a spectral line. We mainly discuss plasma in equilibrium, but briefly mention non-equilibrium ionisation and non-thermal electron distributions. We also summarise the status of atomic data, which are an essential part of the diagnostic process. We then review the methods used to measure electron densities, electron temperatures, the DEM, and relative chemical abundances, and the results obtained for the lower solar atmosphere (within a fraction of the solar radii), for coronal holes, the quiet Sun, active regions and flares.
219 citations
TL;DR: In this article, the authors present a new differential emission measure (DE M) method customised for the AIA bands, to study the thermal structure of ARs at 1 ′′ resolution.
Abstract: We present simultaneous SDO AIA and Hinode EIS observations of the hot cores of active regions (ARs) and assess the dominant contributions to the AIA EUV bands, extending our previous work. We find good agreement between SDO AIA, EVE and EIS observations, using our new EIS calibration and the latest EVE v.3 data. We find that all the AIA bands are multi-thermal, with the exception of the 171 and 335 A, and provide ways to roughly estimate the main contributions directly from the AIA data. We present and discuss new atomic data for the AIA bands, showing that they are now suffi ciently complete to obtain temperature information in the cores of ARs, with the exception of the 211 A band. We found that the newly identified Fexiv 93.61A line is the dominant contribution to the 94 A band, whenever Fexviii is not present. Three methods to estimate the Fexviii emission in this band are presented, two using EIS and one directly from the AIA data. Fexviii emission is often present in the cores, but we found cases where it is formed at 3 MK and not 7 MK, the temperature of peak ion abundance in equilibrium. The best EIS lines for elemental abundance and DE M analysis are discussed. A new set of abundances for many elements are obtained from EIS observations of hot 3 MK loops. The abundances of the elements with low First Ionisation Potential (FIP), relative to those of the high-FIP elements, are found enhanced by about a factor of three, compared to the photospheric values. A measurement of the path length implies that the absolute abundances of the low-FIP elements are higher than the photospheric values by at least a factor of three. We present a new differential emission measure (DE M) method customised for the AIA bands, to study the thermal structure of ARs at 1 ′′ resolution. It was tested on a few ARs, including one observed during the Hi-C rocket flight. We found excellent agreement between predicted and observed AIA count rates and EIS radiances. We found overall little differences in the AIA and Hi-C 193 A images of coronal structures, despite the higher Hi-C resolution (0.25 ′′ ). The Hi-C images and the AIA DE M modelling suggest that some of the cooler loops (below 1 MK) are already resolved by AIA, while the hotter (1.5‐2.5 MK) ‘background’ emission is in most places still unresolved even at the Hi-C resolution. This unresolved emission is sig nificantly lower than previously observed with TRACE and the SOHO CDS and Hinode EIS spectrometers. Its enhancement appears to be mostly due to increased iron abundance. We find an ubiquitous presence of emission at different temperatures that is not co-spatial, and suggest that future high -resolution imaging is done with isothermal bands.
202 citations
Cites background or methods from "EFFECTIVE COLLISION STRENGTHS FOR E..."
...A recent largescale atomic calculation from Tayal & Zatsarinny (2011) didnot resolve the problems with the EUV lines (cf. their Table 4), but should in principle provide better atomic data for the 4f lines....
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...Tayal & Zatsarinny (2011) only provided some A values for the dipole-allowed transitions,however a significant number of forbidden transitions are necessary to redistribute the level population, especially to de-populate the metastable levels for this ion....
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...We therefore built a new ion model where we used the Tayal & Zatsarinny (2011) data but also applied some corrections, based on the Del Zanna (2009b) calculations for the levels numbered 41, 43, 45, and 46....
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...The values calculated byDel Zanna (2009b) have been added to those provided by Tayal & Zatsarinny (2011)....
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TL;DR: In this article, the basic ideas of the B-spline R-matrix approach are reviewed, and the use of the method is illustrated with a variety of applications to atomic structure, electron?atom collisions and photo-induced processes.
Abstract: The basic ideas of the B-spline R-matrix (BSR) approach are reviewed, and the use of the method is illustrated with a variety of applications to atomic structure, electron?atom collisions and photo-induced processes. Special emphasis is placed on complex, open-shell targets, for which the method has proven very successful in reproducing, for example, a wealth of near-threshold resonance structures. Recent extensions to a fully relativistic framework and intermediate energies have allowed for an accurate treatment of heavy targets as well as a fully nonperturbative scheme for electron-impact ionization. Finally, field-free BSR Hamiltonian and electric dipole matrices can be employed in the time-dependent treatment of intense short-pulse laser?atom interactions.
168 citations
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TL;DR: The CHIANTI database as mentioned in this paper is a set of atomic data and transition probabilities necessary to calculate the emission line spectrum of astrophysical plasmas, including atomic energy levels, atomic radiative data such as wavelengths, weighted oscillator strengths and A values, and electron collisional excitation rates.
Abstract: CHIANTI consists of a critically evaluated set of atomic data and transition probabilities necessary to calculate the emission line spectrum of astrophysical plasmas. The data consist of atomic energy levels, atomic radiative data such as wavelengths, weighted oscillator strengths and A values, and electron collisional excitation rates. A set of programs that use these data to calculate the spectrum in a desired wavelength range as a function of temperature and density is also provided. A suite of programs has been developed to carry out plasma diagnostics of astrophysical plasmas. The state-of-the-art contents of the CHIANTI database will be described and some of the most important results obtained from the use of the CHIANTI database will be reviewed.
2,116 citations
TL;DR: The EUV Imaging Spectrometer (EIS) as mentioned in this paper is a two-element, normal incidence design with a backside-illuminated, thinned CCD, which has a significantly greater effective area than previous orbiting EUV spectrographs with typical active region 2 -5 s exposure times in the brightest lines.
Abstract: The EUV Imaging Spectrometer (EIS) on Hinode will observe solar corona and upper transition region emission lines in the wavelength ranges 170 – 210 A and 250 – 290 A. The line centroid positions and profile widths will allow plasma velocities and turbulent or non-thermal line broadenings to be measured. We will derive local plasma temperatures and densities from the line intensities. The spectra will allow accurate determination of differential emission measure and element abundances within a variety of corona and transition region structures. These powerful spectroscopic diagnostics will allow identification and characterization of magnetic reconnection and wave propagation processes in the upper solar atmosphere. We will also directly study the detailed evolution and heating of coronal loops. The EIS instrument incorporates a unique two element, normal incidence design. The optics are coated with optimized multilayer coatings. We have selected highly efficient, backside-illuminated, thinned CCDs. These design features result in an instrument that has significantly greater effective area than previous orbiting EUV spectrographs with typical active region 2 – 5 s exposure times in the brightest lines. EIS can scan a field of 6×8.5 arc min with spatial and velocity scales of 1 arc sec and 25 km s−1 per pixel. The instrument design, its absolute calibration, and performance are described in detail in this paper. EIS will be used along with the Solar Optical Telescope (SOT) and the X-ray Telescope (XRT) for a wide range of studies of the solar atmosphere.
1,050 citations
TL;DR: Superstructure as mentioned in this paper is a general-purpose automatic atomic-structure program that uses multi-configuration type expansions to calculate term energies, intermediate-coupling energy levels, term coupling coefficients, and cascade coefficients.
781 citations
TL;DR: BSR is a general program to calculate atomic continuum processes using the B-spline R-matrix method, including electron–atom and electron–ion collision processes, and radiative processes such as bound–bound transitions, photoionization and polarizabilities.
240 citations
TL;DR: In this article, the authors incorporated the two-body non-fine-structure operators of the Breit-Pauli Hamiltonian, namely contact spin - spin, two body Darwin and orbit - orbit, into the program AUTOSTRUCTURE.
Abstract: We have incorporated the two-body non-fine-structure operators of the Breit - Pauli Hamiltonian, namely contact spin - spin, two-body Darwin and orbit - orbit, into the program AUTOSTRUCTURE. Illustrative results are presented, including some for reactions involving the process of autoionization.
233 citations