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T.P. Ashenfelter, G.J. Mathews (U. of Notre Dame, Center for Astrophysics)
We analyze observed abundance gradients as a function of Galactocentric radius for the external Galaxies NGC4254 and NGC4303. We model the abundance gradients of Nitrogen, Oxygen, and Sulfur for several semi-analytic models. These models isolate the affect of the low metallicity infall term. We conclude that the low metallicity infall models can not adequately explain the steep abundance gradients in these spiral galaxies. Therefore, additional chemical and dynamical mechanisms must be responsible for the observed abundances.