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Journal of Physical Studies 13(3), Article 3901 [16 pages] (2009)
DOI: https://doi.org/10.30970/jps.13.3901 TWO-STAGES OPTIMIZED PHOTOIONIZATION MODELLING OF HII REGION IN BLUE COMPACT GALAXY SBS 0335-052B. Ya. Melekh
Ivan Franko National University of Lviv, Department of
Astrophysics, |
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A new ıt two-stages} method for optimized photoionization modelling of Н{\sc ii} regions was developed. The dividing into two stages of the optimal photoionization model (OPhM) search process is possible owing to the so-called diagnostic ratios (DRs) between emission line intensities in the comparison of model and observed data. DRs are unsensitive to weak variations of the chemical abundances. Thus during the first stage the optimizer determines the ionization structure of the nubular gas using mainly DRs at fixed chemical abundances obtained previously by diagnostic methods. During the second stage the optimizer specifies the abundances of the chemical elements using fluxes in emission lines at the fixed ionization structure of the nebular gas obtained at first stage. On the basis of the observed spectra obtained in [Yu. I Izotov, F. H. Chae, C. B. Foltz, R. F. Green, N. G. Guseva, Astrophys. J., 527, 757 (1999)] using 10-m KeckII telescope from different apertures positioned along Н{\sc ii} region in the blue compact dwarf galaxy (BCDG) SBS 0335-052 the OPhMs of the corresponding part of this object were found using the above ıt two-stages} method. The hight and radius of every cylinder were determined using angular sizes of the apertures and Н{\sc ii} region, respectively and also by the distance to the object. The free parameters of the OPhMs were: the radial hydrogen distribution into corresponding cylinder, filling factor, energy distribution in the ionizing spectra (Lyc-spectrum) and relative abundances of the chemical elements. As a result the distributions of the physical charateristics and the chemical composition over radius of this Н{\sc ii} region were obtained. In the Н{\sc ii} regions surrounding starburst knots the two sources of the direct ionization radiation are possible: stars and hot low density gas into stellar wind cavities. Lyc-spectra in the OPhMs were found independently of the assumptions about the ionization sources nature. Therefore these Lyc-spectra were used for the answer to the question: which of the above ionization sources is dominating in this Н{\sc ii} region? It was shown that Lyc-spectra of stellar wind cavity radiation models better fit the OPhM ones than stellar ionizing cluster models. But both above kinds of modells cannot explain the gap in most OPhMs Lyc-spectra in the wavelength region 1-1.8\,Ry. An attempt was made to explain the above gap by the transition of ionizing radiation through a thin high-density envelope gathered by the stellar wind shock wave.
PACS number(s): 98.58.Hf, 98.52Wz, 98.54Ep, 98.56Wm