Atomic Data Assessment with PyNeb

PyNeb is a Python package widely used to model emission lines in gaseous nebulae. We take advantage of its object-oriented architecture, class methods, and historical atomic database to structure a practical environment for atomic data assessment. Our aim is to reduce the uncertainties in the parameter space (line ratio diagnostics, electron density and temperature, and ionic abundances) arising from the underlying atomic data by critically selecting the PyNeb default datasets. We evaluate the questioned radiative-rate accuracy of the collisionally excited forbidden lines of the N- and P-like ions (O ii, Ne iv, S ii, Cl iii, and Ar iv), which are used as density diagnostics. With the aid of observed line ratios in the dense NGC 7027 planetary nebula and careful data analysis, we arrive at emissivity ratio uncertainties from the radiative rates within 10%, a considerable improvement over a previously predicted 50%. We also examine the accuracy of an extensive dataset of electron-impact effective collision strengths for the carbon isoelectronic sequence recently published. By estimating the impact of the new data on the pivotal [N ii] and [O iii] temperature diagnostics and by benchmarking the collision strength with a measured resonance position, we question their usefulness in nebular modeling. We confirm that the effective-collision-strength scatter of selected datasets for these two ions does not lead to uncertainties in the temperature diagnostics larger than 10%.

Temperature diagnostics of Sulfur III plasma using collision-excitation model

For accurate electron temperature diagnostics, the collision-excitation model is used for Sulfur plasma. Using the calculated Maxwellian average collision strengths at 1000 K, we calculate the electron temperature using the 3s23p2[Formula: see text]D1–3s23p2[Formula: see text]P3, 3s23p2[Formula: see text]S1–3s23p2[Formula: see text]D1 and 3s23p2[Formula: see text]S1–3s23p2[Formula: see text]P3 transitions of Sulfur III. Results show that when the line ratio of 3s23p2[Formula: see text]S1–3s23p2[Formula: see text]D1 and 3s23p2[Formula: see text]D1–3s23p2[Formula: see text]P3 transitions varies from 0.43 to 1, the electron temperature will vary from 0 to [Formula: see text] K, and the electron temperature will decrease with increasing line ratio. This discussion will be important for electron temperature diagnostics of plasma.

Temperature diagnostics for Z-pinches plasma in dependence on compression degree

Calculations of the spectral coefficients for X-ray absorption and spectral brightness's for X-ray radiation were performed for niobium Z-pinch plasma at the temperature of 1 keV and at different plasma densities to determine the compression degree where the spectral lines become indistinguishable. As known, traditional methods of temperature diagnostics of hot dense radiating plasmas are based on analysis of the spectral line shape in dependence on plasma temperature and density. In this case, the interval of photon radiation energies is used, where the spectral lines are well distinguishable in an experiment. On the other hand, Z-pinch plasma has high compression, and an increase of plasma density leads to the deformation of the spectral line shape because of Doppler broadening, Stark broadening, and so-called “additional” broadening of spectral lines that take place in a quantum statistical ensemble of plasma ions and atoms. The traditional method of temperature diagnostics becomes impossible and different methods, which do not use spectral line characteristics, should be applied. The aim of this paper is to determine the density border where the spectral lines become indistinguishable. Important features of the quantum mechanical model, which is known as ion model of plasma, and which is used for calculations in the presented paper, are considered and discussed. A brief review of the theoretical models that have been earlier developed to calculate the radiative opacity characteristics of hot dense plasma is presented as well.

Diagnostics of non-thermal-distributions from solar flare EUV line spectra

Spectral line intensities observed by the Extreme Ultraviolet Variability Experiment (EVE) on board the Solar Dynamics Observatory (SDO) during 2012 March 9 M6.3 flare were used to diagnose a presence of a non-thermal electron distribution represented by a κ-distribution. The diagnosed electron densities ($\approx 2 \times {10^{11}}{\rm{c}}{{\rm{m}}^{ - 3}}$) are affected only a little by the presence of the non-thermal distribution, and are within the uncertainties of observation. On the other hand, the temperature diagnostics based on the line ratios involving different ionization degrees is strongly affected by the type of the electron distribution. The distribution functions diagnosed from relative Fe line intensities demonstrate the presence of strongly non-thermal distributions during the impulsive phase of the flare and later their gradual thermalization.

Accurate effective temperature from Hα profiles

Context. The determination of stellar effective temperature (Teff) in F, G, and K stars using Hα profile fitting is a quite remarkable and powerful tool because it does not depend on reddening and is only slightly sensitive to other atmospheric parameters. Nevertheless, this technique is not frequently used because of the complex procedure needed to recover the profile of broad lines in echelle spectra. As a consequence, tests performed on different models have sometimes provided ambiguous results. Aims. The main aim of this work is to test the ability of the Hα profile fitting technique to derive Teff. We also aim to improve the applicability of this technique to echelle spectra and to test how well 1D + LTE models perform on a variety of F–K stars. We also apply the technique to HARPS spectra and test the reliability and the stability of the HARPS response over several years using the Sun. Methods. We have developed a normalization method for recovering undistorted Hα profiles and we have first applied it to spectra acquired with the single-order Coudé instrument (resolution R = 45 000) at do Pico dos Dias Observatory to avoid the problem of blaze correction. The continuum location around Hα is optimised using an iterative procedure, where the identification of minute telluric features is performed. A set of spectra was acquired with the MUSICOS echelle spectrograph (R = 40 000) to independently validate the normalization method. The accuracy of the method and of the 1D + LTE model is determined using Coudé/HARPS/MUSICOS spectra of the Sun and Coudé-only spectra of a sample of ten Gaia Benchmark Stars with Teff determined from interferometric measurements. HARPS, Coudé, and MUSICOS spectra are used to determine Teff of 43 sample stars. Results. We find that a proper choice of spectral windows of fits plus the identification of telluric features allow for a very careful normalization of the spectra and produce reliable Hα profiles. We also find that the most used solar atlases cannot be used as templates for Hα temperature diagnostics without renormalization. The comparison with the Sun shows that Hα profiles from 1D + LTE models underestimate the solar Teff by 28 K. We find the same agreement between Hα and interferometry and between Hα and Infrared Flux Method: a shallow dependency on metallicity according to the relation Teff = TeffHα − 159[Fe/H] + 28 K within the metallicity range − 0.70 to + 0.40 dex. The comparison with the Infrared Flux Method shows a scatter of 59 K dominated by photometric errors (52 K). In order to investigate the origin of this dependency, we analyzed spectra from 3D models and found that they produce hotter temperatures, and that their use largely improves the agreement with the interferometric and Infrared Flux Method measurements. Finally, we find HARPS spectra to be fully suitable for Hα profile temperature diagnostics; they are perfectly compatible with the Coudé spectra, and lead to the same Teff for the Sun as that found when analysing HARPS spectra over a timespan of more than 7 yr.

Effects of electron distribution anisotropy in spectroscopic diagnostics of solar flares

Aims. We analyzed effects of the bi-Maxwellian electron distribution representing electron temperature anisotropy along and across the magnetic field on the ionization and excitation equilibrium with consequences on the temperature diagnostics of the flare plasma. Methods. The bi-Maxwellian energy distributions were calculated numerically. Synthetic X-ray line spectra of the bi-Maxwellian distributions were calculated using non-Maxwellian ionization, recombination, excitation and de-excitation rates. Results. We found that the anisotropic bi-Maxwellian velocity distributions transform to the nonthermal energy distributions with a high-energy tail. Their maximum is shifted to lower energies and contains a higher number of the low-energy particles in comparison with the Maxwellian one. Increasing the deviation of the parameter p = T∥/T⊥ from 1, changes the shape of bi-Maxwellian distributions and ionization equilibrium, and relative line intensities also increase. The effects are more significant for the bi-Maxwellian distribution with T∥ > T⊥. Moreover, considering different acceleration mechanisms and collisional isotropization it is possible that the bi-Maxwellian distributions with high deviations from the Maxwellian distribution are more probable for those with p > 1 than for those with p < 1. Therefore, distributions with p > 1 can be much more easily diagnosed than those with p < 1. Furthermore, we compared the effects of the bi-Maxwellian distributions on the ionization equilibrium and temperature diagnostics with those for the κ-distributions obtained previously. We found that they are similar and at the present state it is difficult to distinguish between the bi-Maxwellian and κ-distributions from the line ratios.

Temperature diagnostics of plasma under optically-thin conditions

For temperature diagnostics of plasma, using the silicon spectral lines emitted from the solar transition region, under the optically-thin conditions, we discuss temperature diagnostics of the quiet sun in some typical features. For the silicon IV 112.8325 nm and 140.2770 nm spectral lines, using the observed intensity ratio, we calculate the temperature of faint cell center, average cell center, average quiet sun, average network, bright network and very bright network of the quiet sun, and results are in good agreement with those predicted at the [Formula: see text] ionization equilibrium temperature of formation of the silicon IV, and we discuss the temperature when the observed intensity varies from 0.05 to 0.2. This investigation will be significant for temperature diagnostics of plasma under the optically-thin conditions.