Photoionization of Co$^{+}$ and electron-impact excitation of Co$^{2+}$ using the Dirac R-matrix method

TL;DR

This paper calculates photoionization and electron-impact excitation data for cobalt ions using the Dirac R-matrix method, providing essential atomic data for astrophysical models of supernovae and stellar evolution.

Contribution

It presents new relativistic calculations of photoionization cross-sections and collision strengths for low ionization stages of cobalt, filling a gap in atomic data for astrophysical applications.

Findings

Computed photoionization cross-sections for Co II and Co III.

Calculated electron-impact collision strengths for Co III.

Provided data across relevant astrophysical temperature ranges.

Abstract

Modelling of massive stars and supernovae (SNe) plays a crucial role in understanding galaxies. From this modelling we can derive fundamental constraints on stellar evolution, mass-loss processes, mixing, and the products of nucleosynthesis. Proper account must be taken of all important processes that populate and depopulate the levels (collisional excitation, de-excitation, ionization, recombination, photoionization, bound-bound processes). For the analysis of Type Ia SNe and core collapse SNe (Types Ib, Ic and II) Fe group elements are particularly important. Unfortunately little data is currently available and most noticeably absent are the photoionization cross-sections for the Fe-peaks which have high abundances in SNe. Important interactions for both photoionization and electron-impact excitation are calculated using the relativistic Dirac Atomic $R$-matrix Codes (DARC) for low ionization stages of cobalt. All results are calculated up to photon energies of 45 eV and electron energies up to 20 eV. The wavefunction representation of Co III has been generated using GRASP0 by including the dominant 3d$^7$, 3d$^6$[4s, 4p], 3p$^4$3d$^9$ and 3p$^6$3d$^9$ configurations, resulting in 292 fine structure levels. Electron-impact collision strengths and Maxwellian averaged effective collision strengths across a wide range of astrophysically relevant temperatures are computed for Co III. In addition, statistically weighted level-resolved ground and metastable photoionization cross-sections are presented for Co II and compared directly with existing work.