Can stellar dynamics explain the metallicity distributions of presolar grains?

The majority of presolar circumstellar SiC and Al2O3 grains found in meteor ites are inferred to have originated in asymptotic giant branch (AGB) stars that were more metal-rich than the Sun despite being much older than the S un. We test the suggestion of Clayton that this reflects the overwhelming d iffusion of AGB stars from the more metal-rich inner Galaxy to the protosol ar cloud. Weighting the orbital diffusion model of Wielen, Fuchs, & Dettbar n to take into account the higher density of AGE stars and molecular clouds in the inner Galaxy, we find that most parent stars of presolar grains sho uld have diffused to the presolar cloud from their birthplaces at smaller G alactocentric radii. However, the majority of these stars are expected to h ave had subsolar metallicities, in conflict with the grain data. The self-c onsistency of the diffusion model is discussed in the context of stellar ab undance data in the solar neighborhood. The disagreement between the model predictions and the observations might indicate that the inferred metallici ties of presolar grain parent stars are wrong, that the adopted diffusion p arameters are incorrect, and/or that stellar orbital diffusion is not the c orrect explanation for the grain data.