Abstract
The technique of nebular-gas diagnostics was used to find electronic temperatures Te, concentrations ne, relative ion concentrations n(A+i)/n(H+), and chemical abundances A/H for planetary nebulae in the Large and Small Magellanic Clouds. This analysis took into account inhomogeneities of the nebular-gas density in the nebulae. We determined the pre-galactic helium abundance Yp and its rate of enrichment dY/dZ for the envelopes of nine nebulae in the Large Magellanic Cloud. Taken together with the Galaxy’s planetary nebulae and HII regions in blue compact dwarf galaxies, Yp = 0.248 ± 0.002, dY/dZ = 2.31 ± 0.48 and Yp = 0.247 ± 0.002, dY/dZ = 3.03 ± 0.56, respectively, when macroinhomogeneities and macro/microinhomogeneities of the gas density in galactic nebulae are taken into account.
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