ON THE CHEMICAL EVOLUTION OF THE GALACTIC DISK

The chemical evolution of the disk of our Galaxy is studied with numer ical models assuming infall. Several recent (and older) ideas concerni ng the radial dependence of the star formation rate in disk galaxies a re tested, as well as a possible radial dependence of the infall time- scale. Results are compared to a ''minimal set'' of observables, inclu ding those of the solar neighborhood. Among them, the recent evidence for a negligible oxygen gradient in the outer Galaxy constrains severe ly some of the suggested star formation rates. On the basis of our res ults we propose a model with a minimal set of physically plausible ass umptions that satisfies the observational constraints.