Aims. The goal of the CHIANTI atomic database is to provide a set of atomic data for the interpretation of astrophysical spectra emitted by collisionally dominated, high temperature, optically thin sources. Methods. A complete set of ground level ionization and recombination rate coefficients has been assembled for all atoms and ions of the elements of H through Zn and inserted into the latest version of the CHIANTI database, CHIANTI 6. Ionization rate coefficients are taken from the recent work of Dere (2007, A&A, 466, 771) and recombination rates from a variety of sources in the literature. These new rate coefficients have allowed the calculation of a new set of ionization equilibria and radiative loss rate coefficients. For some ions, such as Fe viii and Fe ix, there are significant differences from previous calculations. In addition, existing atomic parameters have been revised and new atomic parameters inserted into the database. Results. For each ion in the CHIANTI database, elemental abundances, ionization potentials, atomic energy levels, radiative rates, electron and proton collisional rate coefficients, ionization and recombination rate coefficients, and collisional ionization equilibrium populations are provided. In addition, parameters for the calculation of the continuum due to bremsstrahlung, radiative recombination and two-photon decay are provided. A suite of programs written in the Interactive Data Language (IDL) are available to calculate line and continuum emissivities and other properties. All data and programs are freely available at http://wwwsolar.nrl.navy.mil/ chianti

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CHIANTI - an atomic database for emission lines. IX. Ionization rates, recombination rates, ionization equilibria for the elements hydrogen through zinc and updated atomic data

In this paper, we study the temperature and density properties of multiple structural components of coronal mass ejections (CMEs) using differential emission measure (DEM) analysis. The DEM analysis is based on the six-passband EUV observations of solar corona from the Atmospheric Imaging Assembly on board the Solar Dynamic Observatory. The structural components studied include the hot channel in the core region (presumably the magnetic flux rope of the CME), the bright loop-like leading front (LF), and coronal dimming in the wake of the CME. We find that the presumed flux rope has the highest average temperature (>8 MK) and density (~1.0 × 109 cm–3), resulting in an enhanced emission measure over a broad temperature range (3 ≤ T(MK) ≤ 20). On the other hand, the CME LF has a relatively cool temperature (~2 MK) and a narrow temperature distribution similar to the pre-eruption coronal temperature (1 ≤ T(MK) ≤ 3). The density in the LF, however, is increased by 2%-32% compared with that of the pre-eruption corona, depending on the event and location. In coronal dimmings, the temperature is more broadly distributed (1 ≤ T(MK) ≤ 4), but the density decreases by ~35%-~40%. These observational results show that: (1) CME core regions are significantly heated, presumably through magnetic reconnection; (2) CME LFs are a consequence of compression of ambient plasma caused by the expansion of the CME core region; and (3) the dimmings are largely caused by the plasma rarefaction associated with the eruption.

https://iopscience.iop.org/article/10.1088/0004-637X/761/1/62/pdf

Differential emission measure analysis of multiple structural components of coronal mass ejections in the inner corona

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.

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Solar UV and X-ray spectral diagnostics

The paper presents an integrated view of the population structure and its role in establishing the ionization state of light elements in dynamic, finite density, laboratory and astrophysical plasmas. There are four main issues, the generalized collisional-radiative picture for metastables in dynamic plasmas with Maxwellian free electrons and its particularizing to light elements, the methods of bundling and projection for manipulating the population equations, the systematic production/use of state selective fundamental collision data in the metastable resolved picture to all levels for collisonal-radiative modelling and the delivery of appropriate derived coefficients for experiment analysis. The ions of carbon, oxygen and neon are used in illustration. The practical implementation of the methods described here is part of the ADAS Project.

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Ionization state, excited populations and emission of impurities in dynamic finite density plasmas: I. The generalized collisional-radiative model for light elements

Dielectronic recombination is a process particularly effective in high-temperature dilute plasmas such as those observed, for example, in astrophysics. This process was first recognised for its noticeable effects on the establishment of ionisation equilibrium in the solar corona. Over the last decade, its importance as a line formation mechanism has been emphasised. It is responsible for spectral lines appearing as satellites to the long-wavelength side of the resonance lines of the highly ionised systems typical of hot plasmas. However, in transient ionising plasmas and for the heavier ions these lines can also be produced by direct excitation of an inner-shell electron. This review is concerned essentially with the analysis and interpretation of the satellite lines in terms of the physical parameters characterising the emitting plasma. Extensive results concerning the astrophysically important hydrogen-like and helium-like ions are summarised. These are compared with the few available high-resolution soft X-ray spectra of solar active regions and flares.

http://iopscience.iop.org/article/10.1088/0034-4885/43/2/002/pdf

Hugh P. Summers

Papers

The ionization equilibrium of hydrogen-like to argon-like ions of elements.

The Density Dependent Ionization Balance of Carbon,Oxygen and Neon in the Solar Atmosphere