CHEMICAL EVOLUTION IN AN INHOMOGENEOUS INTERSTELLAR-MEDIUM

We study the chemical evolution of secondary and primary elements in a model which allows for inhomogeneities in the interstellar medium due to incomplete mixing of stellar ejecta, and a star formation localize d in time and space. The average abundances are the same as the single value obtained from homogeneous models. The inhomogeneous star format ion causes a scatter of the abundances of the ISM. Incomplete mixing h as a strong influence on the relation between nitrogen and oxygen, giv ing rise to flatter N/O-O/H relations, thus mimicking a primary contri bution to the nitrogen synthesis. Comparison with observational data f rom the Galaxy and external galaxies indicates that the probability of star formation is about T = 0.1, in accord with the scatter of stella r metallicities which indicates that the degree of chemical inhomogene ity of the interstellar gas is indeed rather small.