Estimating the Level of Uncertainty in Electron-Impact Excitation and Photoionisation Rates of Low-Ionised Stages of Ni Ions

Luis Fernández-Menchero,Connor Ballance,Catherine Ramsbottom

doi:10.3390/galaxies6030074

Abstract

Ni iv lines can be used as diagnostics for temperature and density for various astrophysical objects. In addition, ionization of Ni2+ is one of the causes of the opacity in the interstellar medium. We calculate the photoionization of Ni2+ and the electron-impact excitation of Ni3+. We use a fully-relativistic Dirac Atomic R-Matrix Code (DARC) method. We include a large set of configurations in the expansion of the wave functions of the target, up to the n=6 atomic shell. We show preliminary results for the photoionization cross-sections of Ni2+ and the electron-impact excitation collision strengths of Ni3+. The expected final results can be implemented in the available software packages for astrophysical plasma simulation, such as CLOUDY. We also show a preliminary estimation of the error of the data by the comparison of different sets of calculations.

Highlights

The R-matrix method [1] has provided a large quantity of electron-impact excitation data within various astrophysical databases such as CLOUDY [2], AtomDB 1, CHIANTI [3] and Open-ADAS 2
Nickel can be important in stellar atmospheres, and models of hot stars in nonlocal thermodynamic equilibrium should take into account these photoionization cross-sections
We presented preliminary results for the photoionisation of Ni2+ and the electron-impact excitation of Ni3+

Summary

Introduction

The R-matrix method [1] has provided a large quantity of electron-impact excitation data within various astrophysical databases such as CLOUDY [2], AtomDB 1 , CHIANTI [3] and Open-ADAS 2. Lowly-charged ions of the iron-peak elements (Feq+ , Coq+ , Niq+ , q = 0 − 3) contribute in general significantly to the opacity of the interstellar gas clouds and other astrophysical objects. Nickel can be important in stellar atmospheres, and models of hot stars in nonlocal thermodynamic equilibrium should take into account these photoionization cross-sections. Photoionization of these species initially in the ground or a low-energy metastable state is the principal process for this opacity. Recent work for a low-ionized iron peak element was performed by Zhang and Pradhan [7,8] They calculated the electron-impact excitation of Fe+. The definitive results will be ready to be used by any modelling code

Method

Level Energies

Preliminary Results

Conclusions