Abundance analysis of selected Cepheids and the galactic distribution of metallicity

Abstract

The determinations are made in order to study the large-scale chemical inhomogeneities across the galactic disk. High-dispersion spectra are obtained of WZ Sgr, X Sgr, Zeta Gem, T Mon and SV Mon. The atmospheric abundances are determined by theoretically synthesizing the selected portions of the stellar spectrum and comparing them with the observed spectra. To compute the theoretical spectrum, the formal solution of the equation of radiative transfer is evaluated numerically with the simplifying assumptions of local thermodynamical equilibrium, plane-parallel geometry, and hydrostatic equilibrium. Since these assumptions are reasonably good for the metallic lines of F-G supergiants, the observations are confined to the phases where Cepheids behave as nonvariable F-G supergiants. The atmospheric abundances of the iron-peak elements Fe, Cr, Ti, and Ca and the heavier s-process elements Y, Ba, La, Ce, and Sm are obtained by synthesizing a selected spectral region in the range 4330-4650 A.