The effect of high-lying levels on atomic models relevant to spectroscopic analyses of solar extreme-ultraviolet spectra

In this work we investigate the effect of including high-lying configurations in the collisional-radiative models used to calculate spectral line intensities recorded by the Solar Ultraviolet Measurement of Emitted Radiation (SUMER) spectrometer on board the SOHO satellite. Many of the emission lines observed by SUMER are attributed to transitions within the L and M electronic shells of ions isoelectronic to sequences from Li I to Na I By using atomic data that are mostly generated by the Hebrew University Lawrence Livermore Atomic Code (HULLAC), we incorporate in the atomic models configurations from higher shells and systematically study their effect on the calculated line intensities in selected ions. The high-lying configurations alter the line intensities through radiative cascades and configuration interaction effects. We find that cascades can significantly enhance the line intensities of the considered ions by up to 60% at temperatures of the ion maximum fractional abundance. The enhancement due to cascades increases with increasing temperature and charge state. The configuration mixing effects can either enhance or reduce the line intensities. Generally, the mixing effect becomes less important for higher charge states.