Photoionization, Recombination, and Radiative Transitions of Atoms and Ions

Abstract

Physical properties such as temperature, density of stars and their chemical compositions can be obtained from detail analysis of their spectra at various wavelengths. Ultraviolet (UV) wavelengths are particularly important as the chromosphere surrounding a star is rich in UV radiation generated by collisional and radiative atomic processes, such as photoionization, electron-ion recombination and bound-bound radiative transitions in the plasma. For both precise diagnostics and astrophysical modelings, accurate atomic parameters for these processes are essential. I report the latest developments in theoretical quantum mechanical calculations, especially under the two international collaborations known as the Opacity Project (OP, The Opacity Project Team 1995, 1996) and the Iron Project (IP, series in A&A 1993-), that have yielded accurate and large-scale atomic data for photoionization cross sections, oscillator strengths, and collision strengths for electron impact excitation of the most astrophysically abundant atoms and ions, and the extension, total and level-specific electron-ion recombination cross sections and rates. The calculations are carried out in anab initio manner using the accurate and powerful R-matrix method, including relativistic fine structure effects for many ions, in the close-coupling approximation.