Abstract:We describe, and present the results of, a new large-scale R-matrix scattering calculation for the electron collisional excitation of Fe viii. We first discuss the limitations of the previous calculations, in particular concerning some strong EUV lines observed in the solar corona by the Hinode EUV Imaging Spectrometer. We then present a new target which represents an improvement over the previous ones for this particularly complex ion. We developed a new method, based on the use of term energy corrections wit… Show more
“…This can even occur for some of the strongest transitions to low-lying levels, as shown, e.g., for Fe xi (Del Zanna et al. 2010b) and Fe viii (Del Zanna and Badnell 2014).…”
Section: Atomic Calculations and Datamentioning
confidence: 80%
“…Semi-empirical corrections are normally not applied to the scattering calculations. However, they can provide significant improvements to the rates (see, e.g., Fawcett and Mason 1989; Del Zanna and Badnell 2014). Fig.…”
Section: Atomic Calculations and Datamentioning
confidence: 99%
“…Several calculations have been carried out (see, e.g., Griffin et al. 2000; Tayal and Zatsarinny 2011), but it was only recently that agreement with the Hinode EIS observations was achieved, with the APAP ICFT R -matrix calculations by Del Zanna and Badnell (2014). The agreement was achieved by adopting a new method which employs semi-empirical corrections within the scattering calculation.…”
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.
“…This can even occur for some of the strongest transitions to low-lying levels, as shown, e.g., for Fe xi (Del Zanna et al. 2010b) and Fe viii (Del Zanna and Badnell 2014).…”
Section: Atomic Calculations and Datamentioning
confidence: 80%
“…Semi-empirical corrections are normally not applied to the scattering calculations. However, they can provide significant improvements to the rates (see, e.g., Fawcett and Mason 1989; Del Zanna and Badnell 2014). Fig.…”
Section: Atomic Calculations and Datamentioning
confidence: 99%
“…Several calculations have been carried out (see, e.g., Griffin et al. 2000; Tayal and Zatsarinny 2011), but it was only recently that agreement with the Hinode EIS observations was achieved, with the APAP ICFT R -matrix calculations by Del Zanna and Badnell (2014). The agreement was achieved by adopting a new method which employs semi-empirical corrections within the scattering calculation.…”
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.
“…This is a general problem present in any method of calculation, and often affecting the strongest lines in an ion, as for Fe XI [32]. The same problem affected the calculations for Fe VIII by [33,34], as discussed in [35,36].…”
Section: Electron Collisional Excitation (Ce)mentioning
confidence: 98%
“…The problem is partially resolved introducing term energy corrections (TEC) in the scattering calculations, as shown in [36]. However, whenever experimental energies are not known or questionable, we have a circular problem.…”
Section: Electron Collisional Excitation (Ce)mentioning
CHIANTI is an atomic database and software package for modeling emission lines and continua from hot astrophysical plasmas. It is freely available to all researchers and has been widely used in the Heliophysics and Astrophysics communities for almost 25 years. In this review, we summarize the properties of the current version of the database and give an overview of the relevant atomic processes. We also discuss progress towards a complete implementation of collisional-radiative modeling, simultaneously solving for atomic level and ion populations for individual elements.
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 highdensity plasma. In addition, the method for computing the differential emission measure used in the CHIANTI software has been changed.
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