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We have obtained spectrophotometric observations of 41 anticenter planetarynebulae (PNe) located in the disk of the Milky Way. Electron temperatures anddensities, as well as chemical abundances for He, N, O, Ne, S, Cl, and Ar weredetermined. Incorporating these results into our existing database of PNabundances yielded a sample of 124 well-observed objects withhomogeneously-determined abundances extending from 0.9-21 kpc in galactocentricdistance. We performed a detailed regression analysis which accounted foruncertainties in both oxygen abundances and radial distances in order toestablish the metallicity gradient across the disk to be:12+log(O/H)=(9.09+/-.05) - (0.058+/-.006) x Rg, with Rg in kpc. While we seesome evidence that the gradient steepens at large galactocentric distances,more objects toward the anticenter need to be observed in order to confidentlyestablish the true form of the metallicity gradient. We find no compellingevidence that the gradient differs between Peimbert Types I and II, nor isoxygen abundance related to the vertical distance from the galactic plane. Ourgradient agrees well with analogous results for H II regions but is steeperthan the one recently published by Stanghellini & Haywood (2010) over a similarrange in galactocentric distance. A second analysis using PN distances from adifferent source implied a flatter gradient, and we suggest that we havereached a confusion limit which can only be resolved with greatly improveddistance measurements and an understanding of the natural scatter in oxygenabundances. Finally, a consideration of recently published chemical evolutionmodels of the Galactic disk suggests that reconciling the current range inpublished oxygen gradients is necessary for adequately constraining parameterssuch as the surface density threshold for star formation and the characteristictimescale for disk formation.

Abundances of Galactic Anticenter Planetary Nebulae and the Oxygen Abundance Gradient in the Galactic Disk