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Journal of Physical Studies 10(2), 148–159 (2006)
DOI: https://doi.org/10.30970/jps.10.148 OPTIMIZED PHOTOIONIZATION MODELLING OF HII REGION IN BLUE COMPACT DWARF GALAXY SBS 0940+544B. Ya. Melekh
Department for Astrophysics, Ivan Franko National University of Lviv, |
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A method for the optimal photoionization model search of HII regions in blue compact dwarf galaxies is proposed. The method consists of two calculation stages. The goal of the first stage is to search for the ionization structure of the nebula at the fixed chemical abundance. The free parameters at this stage are the Lyman continuum spectrum, the radial hydrogen density distribution parameters in HII region, the filling factor, and the helium abundance relative to hydrogen. At the second modelling stage the optimization of the chemical abundance at the found nebular ionization structure is under search. The method is aimed at determinanig the physical chacteristics and chemical composition of the brightest HII region in blue compact dwarf galaxy SBS 0940+544. So as to take into account an underlying stellar absorption effects the helium abundance at the optimal values of the first stage free pameters was optimized in such a way that resulting models relative line intesities of the HeI lines $λ 4026\textup{\AA}$, $λ 4471\textup{\AA}$, $λ 5876\textup{\AA}$, $λ 6678\textup{\AA}$, $λ 7065\textup{\AA}$ were higher than or equal previous observational values. The models values of the relative line intesities were adopted eqiuvalent to the corresponding observational values and both stages were recalculated. A comparative analysis of the results with and without taking into account the underlaying stellar absorption was done. The differences between this and others methods modelling as well as empirical methods for determinanig between this and other methods of physical characteristics and chemical abundance of HII regions are analysed.
PACS number(s): 98.58.Hf, 98.52.Wz, 98.54.Ep, 98.56.Wm