Chemical evolution of the milky way galaxy .2. On the origin of scatter in the age-metallicity relation

We present a model for chemical evolution of the solar vicinity region taking into account both an irregular rate of unenriched gas infall onto the disk and the self-enrichment of stat formation regions with sequential star formation. The evolution of oxygen, iron and deuterium abundances has been followed. It has been found that a present-day and past scatter of oxygen abundances, of iron abundances, and a small scatter of present-day deuterium abundances can be reproduced by the model. The spread in oxygen abundances caused by the self-enrichment of star formation regions with sequential star formation is larger than that for iron abundances. An irregular rate of unenriched gas infall onto the disk results in equal spreads in oxygen and iron abundances. The fraction of scatter due to an episodic gas infall onto the disk seems to be more significant than the fraction of scatter due to the self-enrichment of star formation regions with sequential star formation. The pregalactic deuterium to hydrogen ratio predicted by the model is (D/H)(pr) similar or equal to 2.1 x 10(-5) by number.