Metal abundances in nearby stars and the chemical history of the solar neighbourhood.

A simplified picture of chemical evolution in the solar neighborhood based on the instantaneous recycling approximation and incorporating the effects of recent theoretical assumptions is developed to indicate how these assumptions are related to observational constraints imposed by the dependence of stellar chemical composition on formation time as well as by the statistical distribution of metal abundances in long-lived stars such as G dwarfs. Observational data relating to these questions are reviewed, and the cumulative distribution of metal abundances in G dwarfs is derived from photometric data on nearby stars. The observed distribution is found to be approximately lognormal. Modifications of the simple model are described in detail, including prompt initial enrichment, the early version of metal-enhanced star formation, a more sophisticated version of this model, and inhomogeneous collapse and infall. It is shown that one of the two-component disk-halo models of Ostriker and Thuan (1975) is a particularly successful model.