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We present a new determination of the metallicity gradient in M33, based onKeck/LRIS measurements of oxygen abundances using the temperature-sensitiveemission line [OIII] 4363 A in 61 HII regions. These data approximately triplethe sample of direct oxygen abundances in M33. We find a central abundance of12 + log(O/H) = 8.36+/-0.04 and a slope of -0.027+/-0.012 dex/kpc, in agreementwith infrared measurements of the neon abundance gradient but much shallowerthan most previous oxygen gradient measurements. There is substantial intrinsicscatter of 0.11 dex in the metallicity at any given radius in M33, whichimposes a fundamental limit on the accuracy of gradient measurements that relyon small samples of objects. We also show that the ionization state of neondoes not follow the ionization state of oxygen as is commonly assumed,suggesting that neon abundance measurements from optical emission lines requirecareful treatment of the ionization corrections.

The M33 Metallicity Project: Resolving the Abundance Gradient Discrepancies in M33