From accurate atomic data to elaborate stellar modeling: Structure and collisional data, opacities, radiative accelerations
The new requirements for accuracy and completeness in atomic data from astronomers demand more challenging calculations. Current problems require the relaxation of approximations and detailed studies of different effects like relativistic effects. We carry out relativistic atomic calculations using the Breit-Pauli R-matrix method to generate radiative and collisional data for ions of astrophysical interest. Electron impact excitation of He-like ions have been calculated including relativistic effects, radiation damping and other effects. The comparison with previous works shows differences of up to 30% in the effective collision strengths for the z-line. This line with 3 other transitions between the complexes n=1 and n=2 constitute an important tool for plasma diagnostics and such differences will have strong consequences in the analysis of X-Ray spectra of astronomical objects. We present the relativistic calculation of K? resonances for oxygen ions that are responsible for X-Ray absorption features observed in the spectrum of AGNs. Resonance oscillator strengths have been computed and are in good agreement with the recent experimental and theoretical study of K? photoionization of O II. These data should allow a more complete analysis of X-Ray spectra from AGNs and refine the general picture of such complex objects. We report the first large relativistic calculation of the photoionization cross section of Fe II. The detailed fine structure in the present work agrees well with the experimental results from Kjeldsen et al. (2002) and represents an improvement over the previous non-relativistic results. These data should be useful to the theoretical template of Fe II emissions crucial in the analysis of the UV/O/IR spectrum of AGNs. The new OP opacities are presented, outlining the importance of the inner-shell transitions at high temperature-high density regimes. This new set of data is used to determine constraints on the solar composition and to shed some light on the 'Solar Convection Problem'. While the discrepancies between the two sources (OP and OPAL) are minor for the Rosseland mean opacities, they affect more severely the radiative accelerations. The comparison between the two sets of accelerations outlines their sensitivity to details in monochromatic opacities. The consequences for stellar models are discussed.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:atomic data relativistic calculations x ray diagnostic opacity stellar modelling solar composition star micro diffusion radiative accelerations
Date of Publication:01/01/2005