On the extreme-ultraviolet/ultraviolet plasma diagnostics for nitrogen-like ions from spectra obtained by SOHO/SUMER

In this work we discuss the potential for plasma diagnostics of forbidden transitions from the ground levels in the nitrogen-like ions: Al VII Si VIII P IX S X Ar XII K XIII and Ca XIV We also study the lines emitted by n=3 levels of Si VIII. These transitions fall in the UV spectral range and have been recently observed by the SOHO/SUMER instrument in the solar spectrum. Some of the lines considered in the present study have been measured by SUMER for the first time. We investigate the effects of photospheric radiation, proton collisional excitation, additional configurations, and resonances on level populations, in order to assess the importance of these processes in the calculation of line emissivities. We compare line ratios with observations from SUMER on quiet-Sun and active regions and measure the electron density and temperature of the emitting plasma. We show that in a few cases current atomic data are still not able to reproduce the observations and that further work is required to solve inconsistencies between observations and theoretical predictions.