Research Note

Effects of lowly ionized ions on silicon K-shell absorption spectra

¹ Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, 100012 Beijing, PR China
e-mail: whg;gzhao@nao.cas.cn
² Department of Astronomy, Beijing Normal University, 100875 Beijing, PR China

Received: 27 November 2015
Accepted: 23 March 2016

Abstract

Context. In both astrophysical and laboratory plasmas, K-shell absorption spectra have become powerful diagnostic tools to investigate electron density and temperature. These spectra are also widely used to verify the opacity codes in laboratory settings.

Aims. We report the effects of the low ionization silicon ions, namely from Si I to Si V, which have rarely been considered in previous models, on the K-shell silicon absorption spectra.

Methods. The Si K-shell atomic data were calculated with the flexible atomic code, which is a fully relativistic atomic program with configuration interaction taken into consideration. Detailed level accounting models were employed to calculate the absorption spectra.

Results. We calculate the Si absorption spectra in local thermodynamic equilibrium conditions with temperature and density ranges of 20−70 eV and ~10²⁰ cm^-3 to ~10²² cm^-3, respectively, and show the contributions of the lowly ionized ions to the K-shell absorption spectra of silicon. We also investigate the effects of the different atomic data on the absorption spectra. We find good agreement between our results and these from OPLIB.

Conclusions. We find that the contributions from these lowly ionized ions cannot be neglected at relative low temperatures. Accurate experimental measurements are needed to benchmark the theoretical calculations.