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2021MNRAS.506.5398D - Mon. Not. R. Astron. Soc., 506, 5398-5409 (2021/October-1)

Electron-impact excitation of Ge III and photoionization of Ge II.


Abstract (from CDS):

Energy levels, Einstein A-values, and oscillator strengths are calculated for doubly ionized germanium (Ge III). We have undertaken a study of the electron-impact excitation of Ge III and have also completed a study of the photoionization of Ge II. Ge III target structures were generated using the relativistic GRASP0 package. Several scattering models were investigated to assess the uncertainty quantification of our results. Initially, the lowest lying 64 jj fine-structure levels were included in the close-coupling expansion resulting from 14 non-relativistic configurations. A second larger model was subsequently generated using the GASP package and incorporated the lowest 589 jj fine-structure levels from 17 non-relativistic configurations. Both the DARC (Dirac atomic R-matrix code) and Breit-Pauli parallel suite of R-matrix collision codes were utilized in the scattering calculations to generate the collision strengths for incident electron energies between 0 and 5 Rydbergs and subsequently the Maxwellian-averaged effective collision strengths for temperatures in the range of 1000-200 000 K. The photoionization calculations comprised of two studies, a DARC and a Breit-Pauli calculation incorporating the 250 lowest lying levels. Photoionization cross-sections for Ge II are presented in the range of 0-5 Ryds. Due to the lack of data available in the literature, the present radiative data and electron-impact/photoionization cross-sections are compared between the models presented in this paper. To assess their significance for astrophysics, the data are incorporated into the stellar atmosphere package STERNE. Test models for the heavy-metal subdwarf LS IV-14*116 are not affected by the new data, but models for cooler stars may be sensitive to them.

Abstract Copyright: © 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society

Journal keyword(s): atomic data - atomic processes - opacity - scattering

Simbad objects: 3

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