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We present long slit spectrophotometry considering the presence of thermalinhomogeneities (t^2) of two HII regions in the Small Magellanic Cloud (SMC):NGC 456 and NGC 460. Physical conditions and chemical abundances weredetermined for three positions in NGC 456 and one position in NGC 460, firstunder the assumption of uniform temperature and then allowing for thepossibility of thermal inhomogeneities. We determined t^2 values based on threedifferent methods: i) by comparing the temperature derived using oxygenforbidden lines with the temperature derived using helium recombination lines,ii) by comparing the abundances derived from oxygen forbidden lines with thosederived from oxygen recombination lines, and iii) by comparing the abundancesderived from ultraviolet carbon forbidden lines with those derived from opticalcarbon recombination lines. The first two methods averaged t^2=0.067+-0.013 forNGC 456 and t^2=0.036+-0.027 for NGC 460. These values of t^2 imply that whengaseous abundances are determined with collisionally excited lines they areunderestimated by a factor of nearly 2. From these objects and others in theliterature, we find that in order to account for thermal inhomogeneities anddust depletion, the O/H ratio in low metallicity HII regions should becorrected by 0.25-0.45 dex depending on the thermal structure of the nebula, orby 0.35 dex if such information is not available.

Analysis of two SMC HII Regions Considering Thermal Inhomogeneities: Implications for the Determinations of Extragalactic Chemical Abundances