The effect of high-lying configurations and ionization and recombination processes on analyses of solar and stellar coronal spectra

This work addresses two topics important for the appropriate interpretation of astrophysical spectra. The first is the effect of high-lying levels on the atomic models and the second is the importance of ionization and recombination processes in forming line emission. In the first part of the work we study the influence of high-lying configurations on the calculated intensities of UV lines, particularly of O-like ions, observed by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer aboard the SOHO satellite. The high-lying configurations alter the line intensities through radiative cascades and configuration interaction effects. We find that cascades can significantly enhance the intensities of some lines of the considered ions by up to 65% 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. In a second study, we calculate the theoretical intensities of the soft X-ray Fe16+ lines arising from 2l-3l' transitions using a three-ion collisional-radiative model that includes the contribution of recombination and ionization processes to line formation. Dielectronic recombination is found to be particularly important. The newly calculated line intensities can explain the high values of the 2p-3s / 2p-3d intensity ratios, which are often obtained in astrophysical observations. Observed intensity ratios among the 2p-3s lines are also better reproduced