Sukhorukov A. Formation of the Si I line intensity profiles in one-dimensional models and a three-dimensional model of the Sun.

In this dissertation the formation of Si I lines in the solar spectrum was studied. The line profiles were computed in three semiempirical one-dimensional and in one hydrodynamic three-dimensional model atmospheres both under local thermodynamical equilibrium (LTE) and under departure from it (non-LTE). For the non-LTE computations the most up-to-date atomic model of silicon was constructed. A list of 65 Si I lines was made for the abundance determination. The following non-LTE effects, which influence the formation of Si I spectrum, were determined: a small change of the line opacity and a strong deficit of the line source function. The second effect is a principal contributor that leads to the decrease of the line core intensities and to the increase of the line equivalent widths. The solar silicon abundance was determined in all model atmospheres under LTE and non-LTE. The most reliable value of the abundance is A = 7.549±0.016 dex, which agrees well with the previous recommended values for the solar photosphere and meteorites. It was determined by fitting the observed and theoretical equivalent widths of 65 Si I lines, which were computed under non-LTE in three-dimensional hydrodynamic model of the solar atmosphere for a solar oscillator strength scale by Gurtovenko and Kostik and using the Anstee, Barklem and O'Mara theory to compute the line damping constant gamma6. It was confirmed that the problem of solar anomalous metallicity could be solved only by taking into account the non-LTE effects and the influence of atmospheric inhomogeneities. The following dependencies on the modeling parameters were obtained for the solar silicon abundance value: the dependency on the model selection, on the approximation for van der Waals line broadening, on the oscillator strength scale, on the cross-sections of inelastic collisions with electrons and hydrogen atoms, on the photoionization cross-sections, and on the accepted value of silicon abundance. The solar oscillator strength scale by Gurtovenko and Kostik for Si I lines was analysed and its systematic errors were estimated. The mean total error of this scale is close to zero. The formation of the Si І 1082.7 nm line was studied. The optimal values of two line parameters were estimated and recommended for the further line modeling: the scaling factor for the Drawin formula is SH = 0.1 and the line oscillator strength is lg gf = 0.24. We showed that in order to reproduce observations well, inelastic collisions with hydrogen atoms should be by one order of magnitude more intense in one-dimensional models of atmosphere than in three-dimensional model.