CHIANTI Database Research Articles

CHIANTI—An Atomic Database for Emission Lines—Paper. XVIII. Version 11, Advanced Ionization Equilibrium Models: Density and Charge Transfer Effects

Version 11 of the chianti database and software package is presented. Advanced ionization equilibrium models have been added for low charge states of seven elements (C, N, O, Ne, Mg, Si, and S), and represent a significant improvement especially when modeling the solar transition region. The models include the effects of higher electron density and charge transfer on ionization and recombination rates. As an illustration of the difference these models make, a synthetic spectrum is calculated for an electron pressure of 7 × 1015 cm−3 K and compared with an active region observation from HRTS. Increases are seen in factors of 2–5 in the predicted radiances of the strongest lines in the UV from Si iv, C iv, and N v, compared to the previous modeling using the coronal approximation. Much better agreement (within 20%) with the observations is found for the majority of the lines. The new atomic models better equip both those who are studying the transition region and those who are interpreting the emission from higher-density astrophysical and laboratory plasma. In addition to the advanced models, several ion data sets have been added or updated, and data for the radiative recombination energy loss rate have been updated.

THE 2023 RELEASE OF Cloudy

We describe the 2023 release of the spectral synthesis code Cloudy. Since the previous major release, migrations of our online services motivated us to adopt git as our version control system. This change alone led us to adopt an annual release scheme, accompanied by a short release paper, the present being the inaugural. Significant changes to our atomic and molecular data have improved the accuracy of Cloudy predictions: we have upgraded our instance of the Chianti database from version 7 to 10; our H- and He-like collisional rates to improved theoretical values; our molecular data to the most recent LAMDA database, and several chemical reaction rates to their most recent UDfA and KiDA values. Finally, we describe our progress on upgrading Cloudy's capabilities to meet the requirements of the X-ray microcalorimeters aboard the upcoming XRISM and Athena missions, and outline future developments that will make Cloudy of use to the X-ray community.

CHIANTI—An Atomic Database for Emission Lines. XVII. Version 10.1: Revised Ionization and Recombination Rates and Other Updates* *Released on 2023 July 17.

The CHIANTI atomic database provides sets of assessed data that are used for simulating spectral observations of astrophysical plasmas. This article describes updates that will be released as version 10.1 of the database. A key component of CHIANTI is the provision of ionization and recombination rates that are used to compute the ionization balance of a plasma over a range of temperatures. Parameters for calculating the ionization rates of all stages of ions from H through Zn were compiled and inserted into the CHIANTI database in 2009. These were based on all measurements that were available at the time and supplemented with distorted wave calculations. Since then, there have been a number of new laboratory measurements for ions that produce spectral lines that are commonly observed. Parameters have been fit to these new measurements to provide improved ability to reproduce the ionization cross sections and rate coefficients, and these are added to the database. CHIANTI 10.1 also includes new recombination rates for the phosphorus isoelectronic sequence, and the updated ionization and recombination rates have been used to calculate a new ionization equilibrium file. In addition, CHIANTI 10.1 has new electron collision and radiative data sets for eight ions in the nitrogen and oxygen isoelectronic sequences and updated energy level and wavelength data for six other ions.

Charge State Calculation for Global Solar Wind Modeling

Abstract The charge state composition of the solar wind carries information about the electron temperature, density, and velocity of plasma in the solar corona that cannot always be measured with remote sensing techniques, due to limitations in instrumental sensitivity and field of view as well as line-of-sight integration issues. However, in situ measurements of the wind charge state distribution only provide the end result of the solar wind evolution from the source region to the freeze-in point. By using 3D global modeling it is possible to follow solar wind plasma parcels of different origin along the path of their journey and study the evolution of their charge states as well as the driving physical processes. For this purpose, we implemented nonequilibrium ionization calculations within the Space Weather Modeling Framework’s solar corona and inner heliosphere modules, to the Alfvén Wave Solar Model (AWSoM). The charge state calculations are carried out parallel to the AWSoM calculations, including all the elements and ions whose ionization-recombination rates are included in the CHIANTI database, namely, from H to Zn. In this work, we describe the implementation of the charge state calculation, and compare simulation results to in situ measurements from the Advanced Composition Explorer and Ulysses spacecraft, and study charge state evolution of plasma parcels along different wind trajectories and wind types.

KAPPA: A Package for the Synthesis of Optically Thin Spectra for the Non-Maxwellian κ-distributions. II. Major Update to Compatibility with CHIANTI Version 10

Abstract KAPPA is a database and software for the calculation of the optically thin spectra for the non-Maxwellian κ-distributions that were recently diagnosed in the plasma of solar coronal loops, flares, as well as in the transition region. KAPPA is based on the widely used CHIANTI database and reproduces many of its capabilities for κ-distributions. Here we perform a major update of the KAPPA database, including a near-complete recalculation of the ionization, recombination, excitation, and deexcitation rates for all ions in the database, as well as an implementation of the two-ion model for calculations of relative-level populations (and intensities) if these are modified by ionization and recombination from or to excited levels. As an example of KAPPA usage, we explore novel diagnostics of κ, and show that O iii lines near 500 and 700 Å provide a strong sensitivity to κ, with some line intensity ratios changing by a factor of up to 2–4 compared to Maxwellian. This is much larger than previously employed diagnostics of κ.

R-matrix electron-impact excitation data for the O-like iso-electronic sequence

Context. Astrophysical plasma codes are built on atomic databases. In the current atomic databases, R-matrix electron-impact excitation data of O-like ions are limited. The accuracy of plasma diagnostics with O-like ions depends on the availability and accuracy of the atomic data. This is particularly relevant in the context of future observatories equipped with the next generation of high-resolution spectrometers. Aims. We aim to obtain level-resolved effective collision strengths of O-like ions from Ne III to Zn XXIII (i.e. Ne2+ to Zn22+) over a wide range of temperatures. This includes transitions up to nl = 5d for each ion. We also aim to assess the accuracy of the new data, as well as their impact on solar atmosphere plasma diagnostics, compared to those available within the CHIANTI database. Methods. Large-scale R-matrix intermediate coupling frame transformation calculations were performed systematically for the O-like iso-electronic sequence. For each ion, 630 fine-structure levels were included in both the configuration interaction target and close-coupling collision expansions. Results. Our results (energy levels, oscillator strengths, and effective collision strengths) of selected ions across the iso-electronic sequence are compared with those in archival databases and the literature. For the selected ions throughout the iso-electronic sequence, we find general agreement with the few previous R-matrix calculations of collision strengths. We illustrate the improvements for a few solar plasma diagnostics over existing CHIANTI atomic models based on distorted wave (DW) data. The electron-impact excitation data are archived according to the Atomic Data and Analysis Structure (ADAS) data class adf04 and will be available in OPEN-ADAS.

Introduction of Zeeman splitting in CHIANTI

High-resolution spectra emitted by laboratory plasmas provide invaluable diagnostic tools for the measurement of plasma properties. To be implemented, they require a large amount of atomic data and transition rates, which are available in several spectral codes. In this paper we present a new feature added to the CHIANTI code, which allows us to calculate the Zeeman splitting of spectral lines in the presence of a magnetic field with known intensity and orientation. When combined with the CHIANTI database and software to calculate level populations and line emissivities, this new feature returns the emissivities in all four Stokes parameters, that can be utilized for the measurement of the magnetic field inside laboratory plasma chambers, along with other plasma parameters. This new feature can be applied to the analysis of the emission of laboratory plasmas created in different devices.

Forward Synthesis of Polarized Emission in Target DKIST Coronal Lines Applied to 3D MURaM Coronal Simulations

Self-consistent magnetohydrodynamic simulations of the solar corona with fine ( $\lesssim10$ km) grid scales are now being realized in parallel to advancements in high-resolution coronal spectropolarimetry provided by the National Science Foundation’s Daniel K. Inouye Solar Telescope (DKIST). We investigate the synthesis of polarized emission in the presence of apparent coronal fine structure exhibited by 3D MURaM coronal simulations for the key polarized spectral lines targeted by DKIST, namely Fe xiv $\lambda5303$ , Fe xi $\lambda7892$ , Fe xiii $\lambda10746$ , Fe xiii $\lambda10798$ , Si x $\lambda14301$ , and Si ix $\lambda39343$ . To benchmark our calculations, we provide detailed comparisons between the employed polarized line formation theory and established scalar line synthesis tools provided by the Chianti database team. To accelerate polarized synthesis for large simulations, we create efficient lookup tables based on atomic models significantly larger than previous studies. The spectral data cubes we describe provide a useful guide for the new era of multi-spectral DKIST coronal diagnostics as we discuss specific analysis techniques and challenges.

SPECTRUM: Synthetic Spectral Calculations for Global Space Plasma Modeling

Abstract High-resolution spectroscopy is the most accurate tool for measuring the properties of the solar corona. However, interpreting measured line intensities and line profiles emitted by the optically thin solar corona is complicated by line-of-sight (LOS) integration, which leads to measuring weighted averages of the plasma properties along the LOS. LOS integration effects can be removed by combining CHIANTI spectral emissivities with a 3D global model of the solar corona to calculate the contribution of all structures along the LOS to the measured intensities. In this paper, we describe SPECTRUM, a postprocessing tool that can calculate the emission from the optically thin solar corona by combining 3D magnetohydrodynamic (MHD) space plasma simulation results with the CHIANTI database. Doppler-shifted, nonthermal line broadening due to low-frequency Alfvén waves and anisotropic proton and isotropic electron temperatures can be individually taken into account during calculations. Synthetic spectral calculations can then be used for model validation, for interpretation of solar observations, and for forward modeling purposes. SPECTRUM is implemented within the Space Weather Modeling Framework (SWMF) and is therefore publicly available. In this paper, we describe the SPECTRUM module and show its applications by comparing synthetic spectra using simulation data by the 3D MHD Alfvén Wave Solar Model with observations done by the Hinode/Extreme-ultraviolet Imaging Spectrometer during Carrington rotations 2063 and 2082.

A chemistry and cooling module for the NIRVANA code

Context. Gas cooling and other thermal processes in the interstellar medium are intimately related to its chemical evolution. To accurately model chemical processes in large-scale gas-dynamical simulations the usage of existing sophisticated astrochemical networks is presently impossible due to prohibitive computational costs. A viable way to deal with the problem is by the design of reduced chemical networks that satisfactorily reproduce the most important features of the more elaborate networks. Aims. A chemistry and cooling module for the interstellar medium is developed that is realistic for temperatures T ≳ 50 K and for densities up to n ≈ 1010 m−3 at the limit of non-ionizing and non-dissociating background radiation. The module is incorporated into the multiphysics, adaptive-grid code NIRVANA and aims at improving gas-dynamical simulations by explicitly following non-equilibrium chemistry and gas cooling. Methods. The presented chemical network covers 121 species and 426 reactions. It includes a fully-fledged ionization subnetwork for the ten elements H, D, He, C, N, O, Mg, Ne, Si, and Fe, chemical schemes for the formation and destruction of the important molecular coolants H2, H2O, CO, and OH, a model for dust-catalytic reactions and cosmic ray effects. Metal line cooling was computed from first principles by solving for the energy level population for each ion. Atomic data was adopted from the latest version of the Chianti database. The treatment of rotovibrational line cooling from molecules was based on various up-to-date literature sources. Results. The implementation has been validated by performing both equilibrium and non-equilibrium (time-dependent) computations. The equilibrium results overall confirm the temperature dependence of chemical abundances and the gas cooling rate that has been found in similar studies. In particular, the ionization structure in the high-temperature regime, at T ≳ 2 × 104 K, excellently agrees with literature results. In the non-equilibrium calculations, the occurrence of ionization lags are prominent and distinguishes the resulting non-equilibrium cooling from equilibrium cooling. In the low-temperature regime, at T ≲ 2 × 104 K, the non-equilibrium cooling rate can be enhanced by up to two orders of magnitude compared to the equilibrium value. Conclusions. The NIRVANA chemistry and cooling module has been successfully tested against literature results. The underlying chemical network is best compared to recently developed networks in the limit of no radiation with differences appearing in the treatment of dust, cosmic ray heating, and in the choice of reaction coefficients. The gas cooling experiments indicate that a reduction of the present network size seems possible under certain conditions by skipping the elements N and Mg, which turn out to be less important coolants compared to the conglomerate of C, O, Si, and Fe coolants.

Magnetic reconnection in the low solar chromosphere with a more realistic radiative cooling model

Magnetic reconnection is the most likely mechanism responsible for the high temperature events that are observed in strongly magnetized locations around the temperature minimum in the low solar chromosphere. This work improves upon our previous work [Ni et al., Astrophys. J. 852, 95 (2018)] by using a more realistic radiative cooling model computed from the OPACITY project and the CHIANTI database. We find that the rate of ionization of the neutral component of the plasma is still faster than recombination within the current sheet region. For low β plasmas, the ionized and neutral fluid flows are well-coupled throughout the reconnection region resembling the single-fluid Sweet-Parker model dynamics. Decoupling of the ion and neutral inflows appears in the higher β case with β0=1.46, which leads to a reconnection rate about three times faster than the rate predicted by the Sweet-Parker model. In all cases, the plasma temperature increases with time inside the current sheet, and the maximum value is above 2×104 K when the reconnection magnetic field strength is greater than 500 G. While the more realistic radiative cooling model does not result in qualitative changes of the characteristics of magnetic reconnection, it is necessary for studying the variations of the plasma temperature and ionization fraction inside current sheets in strongly magnetized regions of the low solar atmosphere. It is also important for studying energy conversion during the magnetic reconnection process when the hydrogen-dominated plasma approaches full ionization.

Intensity of emission lines of the quiescent solar corona: comparison between calculated and observed values

The paper reports the results of calculations of the center-to-limb intensity of optically thin line emission in EUV and FUV wavelength ranges. The calculations employ a multicomponent model for the quiescent solar corona. The model includes a collection of loops of various sizes, spicules, and free (inter-loop) matter. Theoretical intensity values are found from probabilities of encountering parts of loops in the line of sight with respect to the probability of absence of other coronal components. The model uses 12 loops with sizes from 3200 to 210000 km with different values of rarefaction index and pressure at the loop base and apex. The temperature at loop apices is 1 400 000 K. The calculations utilize the CHIANTI database. The comparison between theoretical and observed emission intensity values for coronal and transition region lines obtained by the SUMER, CDS, and EIS telescopes shows quite satisfactory agreement between them, particularly for the solar disk center. For the data acquired above the limb, the enhanced discrepancies after the analysis refer to errors in EIS measurements.

Интенсивность эмиссионных линий короны спокойного Солнца: сравнение расчетных и наблюдательных данных

The paper reports the results of calculations of the center-to-limb intensity of optically thin line emission in EUV and FUV wavelength ranges. The calculations employ a multicomponent model for the quiescent solar corona. The model includes a collection of loops of various sizes, spicules, and free (inter-loop) matter. Theoretical intensity values are found from probabilities of encountering parts of loops in the line of sight with respect to the probability of absence of other coronal components. The model uses 12 loops with sizes from 3200 to 210000 km with different values of rarefaction index and pressure at the loop base and apex. The temperature at loop apices is 1 400 000 K. The calculations utilize the CHIANTI database. The comparison between theoretical and observed emission intensity values for coronal and transition region lines obtained by the SUMER, CDS, and EIS telescopes shows quite satisfactory agreement between them, particularly for the solar disk center. For the data acquired above the limb, the enhanced discrepancies after the analysis refer to errors in EIS measurements.

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.

Observational Signatures of a Kink-unstable Coronal Flux Rope Using Hinode/EIS

Abstract The signatures of energy release and energy transport for a kink-unstable coronal flux rope are investigated via forward modeling. Synthetic intensity and Doppler maps are generated from a 3D numerical simulation. The CHIANTI database is used to compute intensities for three Hinode/EIS emission lines that cover the thermal range of the loop. The intensities and Doppler velocities at simulation-resolution are spatially degraded to the Hinode/EIS pixel size (1″), convolved using a Gaussian point-spread function (3″), and exposed for a characteristic time of 50 s. The synthetic images generated for rasters (moving slit) and sit-and-stare (stationary slit) are analyzed to find the signatures of the twisted flux and the associated instability. We find that there are several qualities of a kink-unstable coronal flux rope that can be detected observationally using Hinode/EIS, namely the growth of the loop radius, the increase in intensity toward the radial edge of the loop, and the Doppler velocity following an internal twisted magnetic field line. However, EIS cannot resolve the small, transient features present in the simulation, such as sites of small-scale reconnection (e.g., nanoflares).

The CHIANTI database, a consistency check on the accuracy of the stored cross-section values in He i to O i isoelectronic sequence ions

CHIANTI is an atomic database with software for calculating emission properties. It is extensively used in deriving the atomic properties of spectra recorded from astrophysical and low density laboratory plasmas. In order to obtain an insight into the accuracy of the CHIANTI calculated level populations, a consistency check was conducted along the He i, Be i, B i, C i, N i, and O i isoelectronic sequences. In the evaluation process, levels of the ground configuration and the first and second excited configurations were considered. These are the levels responsible for most of the spectral lines used when deriving the plasma properties of astrophysical objects. As is documented below, the accuracy of the CHIANTI level population calculations depends on the particular ion, level and on the electron density. Under some conditions the calculations appear quite robust while in others they are not.

CHIANTI – An atomic database for emission lines. Version 8

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.

Ionisation Equilibrium for the Non-Maxwellian Electron n $n$ -Distributions in Solar Flares: Updated Calculations

We use the latest available atomic data to calculate the ionisation and recombination rates for the non-Maxwellian \(n\)-distributions, which were shown previously to provide a good fit to the enhanced intensities of dielectronic satellite lines during solar flares. The ionisation and recombination coefficients are subsequently used to derive the ionisation equilibrium. To do so, we consider odd values of \(n\) ranging from 1 to 19, i.e., from Maxwellian to strongly non-Maxwellian cases. These calculations involve all elements with proton number up to 30, i.e., H to Zn. The \(n\)-distributions modify both the ionisation and the recombination rates. The ionisation rates decrease more steeply at lower pseudo-temperatures, while the radiative recombination rate is reduced due to a lower number of low-energy electrons. The peaks of the dielectronic recombination rates become narrower. These changes are reflected in the ionisation equilibrium. Ion abundance peaks become narrower and can also be shifted, mostly towards higher temperatures. The He-like ions are an important exception, as they are formed in a larger temperature range than that for the Maxwellian distribution. The ions Si xiii – xiv used previously for the diagnostics of the \(n\)-distributions are affected only weakly, confirming the determination of \(n\). The ionisation equilibria are available as the electronic supplementary material in a format compatible with the CHIANTI database.

ELECTRON DENSITY OF ACTIVE REGION OUTFLOWS MEASURED BY THE EUV IMAGING SPECTROMETER ON BOARDHINODE

In order to better understand the nature of active region outflows, the electron density was measured by using a density-sensitive line pair Fe xiv 264.78A/274.20A.Since coronal line profiles of the outflow region are composed of a major component with a Doppler shift of < 10 km s^-1 and a minor component (enhanced blue wing: EBW) blueshifted by up to 100 km s^-1, we extracted EBW from the line profiles through double-Gaussian fitting. We tried applying the simultaneous fitting to those two Fe xiv lines with several physical restrictions. Electron density for both components (n_Major and n_EBW, respectively) was calculated by referring to the theoretical intensity ratio as a function of electron density as per the CHIANTI database. We studied six locations in the outflow regions around NOAA AR10978. The average electron density was n_Major = 10^(9.16 +- 0.16) cm^-3 and n_EBW = 10^(8.74 +- 0.29) cm^-3. The magnitude relationship between n_Major and n_EBW was opposite in the eastern and western outflow regions. The column depth was also calculated for each component, which leads to the result that the outflows possess only a small fraction (~ 0.1) in the eastern region, while they dominate over the major component in the line profiles by a factor of five in the western region. When taking into account the extending coronal structures, the western region can be thought to represent the mass leakage. In contrast, we suggest a possibility that the eastern region actually contributes to the mass supply to coronal loops.

KAPPA: A PACKAGE FOR SYNTHESIS OF OPTICALLY THIN SPECTRA FOR THE NON-MAXWELLIAN κ -DISTRIBUTIONS BASED ON THE CHIANTI DATABASE

The non-Maxwellian $\kappa$-distributions have been detected in the solar transition region and flares. These distributions are characterized by a high-energy tail and a near-Maxwellian core and are known to have significant impact on the resulting optically thin spectra arising from collisionally dominated astrophysical plasmas. We developed the KAPPA package (http://kappa.asu.cas.cz) for synthesis of such line and continuum spectra. The package is based on the freely available CHIANTI database and software, and can be used in a similar manner. Ionization and recombination rates together with the ionization equilibria are provided for a range of $\kappa$ values. Distribution-averaged collision strengths for excitation are obtained by an approximate method for all transitions in all ions available within CHIANTI. The validity of this approximate method is tested by comparison with direct calculations. Typical precisions of better than 5% are found, with all cases being within 10%. Tools for calculation of synthetic line and continuum intensities are provided and described. Examples of the synthetic spectra and SDO/AIA responses to emission for the $\kappa$-distributions are given.