The chemical evolution of star-forming viscous discs

The basic equations determining the chemical evolution of a star forming viscous disc, taking into account the effects of radial flows and diffusion in the disc, are formulated. The metallicity distribution in the final stellar discs is determined. It is shown that, for parameter values which lead to the formation of stellar discs with nearly exponential surface density distributions, the disc's metallicity distributions are characterized by a 'universal' shape. The results of the model calculations are compared with observational data on the radial metallicity distribution in the old galactic disc. A reasonable agreement between observations and model results is found. (author)