A New Ionization Correction scheme for He+/H+ and the determination of the helium abundance inHii regions

We have developed a New Ionization Correction Factor (ICF) scheme for He⁺ based on the definition of the radiation softness parameter (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⁺–He⁰ ionization structure whilst remaining insensitive to other nebular parameters. The ICF() 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.