2000ApJ...542L..25O

A rudimentary, one-zone, closed-box model for inhomogeneous chemical evolution is offered as an alternative reference model, distinct from the Simple Model, in the limit of no mixing. The metallicity distribution functions (MDFs) of Galactic halo and bulge stars can be matched by varying a single evolutionary parameter, nQ. Q is the filling factor of contaminating regions, and n is the number of star-forming generations. Therefore, Q and n have equivalent roles, and combinations of n and Q yield systems with different metallicities at any given age. The model also revises the interpretation of observed MDFs. Unevolved systems probe the metallicity distribution f(z) of parent enrichment events; for example, the high-metallicity tail of the halo distribution agrees with a power-law f(z).