A new ionization correction scheme for He(+)/H(+) and the determination of the helium abundance in H II regions

Vilchez, J. M.
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(Instituto de Astrofisica de Canarias and Comision Interministerial de Ciencia y Tecnologia, Summer School on Evolutionary Phenomena in Galaxies, Puerto de la Cruz, Spain, July 4-15, 1988) Astrophysics and Space Science (ISSN 0004-640X), vol. 157, no. 1-2, July 1989, p. 9-14.

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A new ionization correction factor (ICF) scheme for He(+) is developed, based on the definition of the radiation softness parameter eta (Vilchez and Pagel, 1988) which is very sensitive to the effective temperature of the ionizing star(s) and, therefore, a good indicator of the He(+)-He(0) ionization structure while remaining insensitive to other nebular parameters. The ICF(eta) relationship is obtained making use of the Stasinska (1980, 1982) photoionization models. After comparison with previous semiempirical approaches in the literature and its application to a selected sample of abundances, it is found that this ICF scheme seems a powerful tool for the determination of He abundances, particularly for objects of intermediate to low excitation.