Melekh B. Investigation of physical characteristics and chemical composition of HII regions in blue compact dwarf galaxies

The method for calculation of Lc-spectra, based on the observed fluxes from HII regions, was modified. Ionizing Lc-spectra more than 40 HII regions in blue compact dwarf galaxies (BCDG) nucleus were obtained using this method. Two independent methods for determination of physical parameters and chemical composition in these HII regions were developed. The first method are based on the calculation of photoionized models (PhM) grid of these objects. Ion abundances obtained as a result of diagnostics of predicted PhMs grid spectra were used for derivation of new ionization-correction factors (ICF) expressions for the HII region in BCDG. These expressions were tested on the reproduction of the chemical composition assumed in PhMs grid. New expression for the ICF(He) was found. The second method is based on the calculation of the optimized PhMs (OPhMs). The OPhMs of 12 HII regions in BCDG were calculated. OPhMs with deviations from spherical geometry and with sinusoidal density fluctuation were calculatedand in result was obtained that thus deviations have not important influence on the determination of primordial helium (Yp) abundance and their enrichment (dY/dZ) during chemical evolution of BCDGs. Using these two methods and observed spectra, obtained by Izotov et al. (1994-1997), physical parameters and chemical composition in HII regions of BCDGs were determined. In result primordial helium abundance (Yp=0.244+/-0.004 from new ICFs and Yp=0.245+/-0.004 from OPhMs) and their enrichment (dY/dZ=8.8+/-4.6 from new ICFs and dY/dZ=4.2+/-3.5 from OPhMs) were obtained.