NLTE formation of the silicon spectrum: silicon abundance in three-dimensional model of the solar atmosphere

1Shchukina, NG, 1Sukhorukov, AV
1Main Astronomical Observatory of the National Academy of Sciences of Ukraine, Kyiv, Ukraine
Kinemat. fiz. nebesnyh tel (Online) 2013, 29(1):26-49
Start Page: Solar Physics
Language: Russian

We investigated the NLTE formation of the silicon spectrum in a three-dimensional (3D) hydrodynamical snapshot of the solar atmosphere using realistic atomic model. It is shown that the joint action of line source function deficits and line opacity excesses caused by the overpopulation of the lower levels of Si I lines produces more pronounced effects on line central depths and equivalent widths in intergranular regions than in granular ones. We fitted the silicon abundances AW and AD from the equivalent widths W and central depths D of 65 Si I lines using the 3D snapshot. The total silicon abundance error caused by the neglect of NLTE and 3D effects and by uncertainties in the van der Waals broadening constant 6 is shown to be –0.1 dex. Employing the semi-classical theory of Anstee, Barklem and O’Mara to calculate g6, we get good agreement between AW and AD values. The average difference AW –AD does not exceed 0.01 dex both for NLTE and LTE. The abundances AW appear to be in disagreement with AD values when Unsld’s approximation for the calculation of γ6 is applied. We analysed the “solar” oscillator strength scale of Gurtovenko and Kostik and experimental oscillator strength scales of Garz and Becker et al. The “solar” oscillator strengths lggfW are shown to minimize the trends with line strength in the derived individual abundances AW and AD as well as their differences AW – AD and standard deviations. Using the 3D snapshot, “solar” oscillator strengths and ABO theory, we obtained that silicon NLTE-abundance equals 7.549±0.016. This value is in good agreement with the CI chondrite meteoritic abundance recommended by Grevesse and Sauval.

Keywords: atmosphere, NLTE-formation, Sun

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