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%.

Reply to the comment by K.M. Aggarwal on “Collision strength and effective collision strength for Ba XLVIII”

We show that the comment of K.M. Aggarwal (2018, Can. J. Phys. 96(10), doi: https://www.nrcresearchpress.com/doi/pdf/10.1139/cjp-2017-0842 ), although being only marginally relevant to the content of the original paper (2017, Can. J. Phys. 95(2), doi: https://www.nrcresearchpress.com/doi/pdf/10.1139/cjp-2016-0513 ), misinterprets our results and leads to an incorrect conclusion.

Calculation of averaged collision strength of magnesium for non-Maxwellian distributions in plasma

In this paper, kappa and Druyvesteyn distributions of electronic velocity are discussed for non-Maxwellian distribution. For accurate temperature and electron density diagnostics of Magnesium plasma, for the Magnesium VIII [Formula: see text] to [Formula: see text] transitions, we calculate kappa averaged collision strengths for [Formula: see text] = 2, 3 and 5 and the Druyvesteyn averaged collision strengths for [Formula: see text] = 1.5, 2 and 3, for temperature between [Formula: see text] and [Formula: see text]. Results indicate that the kappa averaged collision strengths are slightly larger than those for the Maxwellian distribution, and the Druyvesteyn averaged collision strengths are slightly smaller than those for the Maxwellian distribution, furthermore, the averaged collision strengths will be close to those for Maxwellian distribution with increasing [Formula: see text] for the kappa distribution and with decreasing [Formula: see text] for the Druyvesteyn distribution. The excitation rate coefficients are also calculated for Maxwellian and non-Maxwellian distributions. This discussion will be significant in study of plasma for the non-Maxwellian distribution.

Comment on “Collision strength and effective collision strength for Br XXVII” by Goyal et al. [Can. J. Phys. 95, 1127 (2017)]

In a recent paper, Goyal et al. [Can. J. Phys. 95, 1127 (2017)] have reported results for collision strengths (Ω) and effective collision strengths (ϒ) for transitions among the lowest 52 levels of F-like Br XXVII. For their calculations, they have adopted the Dirac atomic R-matrix code (DARC) and the flexible atomic code (FAC). In this comment we demonstrate that their results for both parameters are erratic, inaccurate, and unreliable.

Comment on “Collision strength and effective collision strength for Ba XLVIII” by Mohan et al. [Can. J. Phys. 95, 173 (2017)]

In a recent paper, Mohan et al. [Can. J. Phys. 95, 173 (2017)] have reported results for collision strengths (Ω) and effective collision strengths (ϒ) for transitions from the ground to higher 51 excited levels of F-like Ba XLVIII. For the calculations of Ω, the Dirac atomic R-matrix code (DARC) and the flexible atomic code (FAC) have been adopted, to facilitate a direct comparison. However, for the subsequent calculations of ϒ, DARC alone has been employed. In this comment, we demonstrate that while their limited results for Ω are comparatively reliable, for ϒ they are not, particularly for the allowed transitions and at lower temperatures. Apart from the unexpected behaviour, their ϒ values are overestimated for several transitions, by about a factor of two.

Averaged collision strength of Carbon Π ion of Druyvesteyn distribution in plasma

Non-Maxwellian distribution has been found in laboratory and space plasma in recent years. In this paper, averaged collision strengths of Carbon [Formula: see text] ion 133.53 nm are calculated for Druyvesteyn distribution for the non-Maxwellian distribution, when temperatures vary from 10[Formula: see text] K to 10[Formula: see text] K. Results indicate that significant differences between the averaged collision strengths occur for the Druyvesteyn distribution and the Maxwellian distribution, furthermore, for the Maxwellian distribution and the Druyvesteyn distribution with any characterizing parameter x, the averaged collision strengths increase with increasing temperature, and the averaged collision strengths are close to those of the Maxwellian distribution when the characterizing parameter x is close to [Formula: see text]. This calculation is significant for non-Maxwellian plasma.

Collision strength and effective collision strength for Br XXVII

Collision strengths for all 1326 transitions among lowest 52 fine-structure levels of Br XXVII have been computed using Dirac atomic R-matrix code (DARC). Resonances in the threshold region have been completely resolved and the contributions of these resonances to allowed and forbidden transitions have been presented. The partial collision strength for each angular momentum has been studied graphically. Effective collision strengths have also been determined within the temperature range for all 1326 transitions among the lowest 52 levels. Target state energies of the lowest 52 fine-structure levels have been computed from the multi-configuration Dirac–Fock method (MCDF). Additionally, similar calculations with the relativistic distorted wave method and flexible atomic code (FAC) have also been performed to check the accuracy of our results. The present work represents a new and significant work with improvement in the field. We believe that our presented data of collision and effective collision strengths may be useful in the future for benchmark calculations and for plasma diagnostics.