Chemical evolution of the galactic halo. I - Effects of possible mass segregation mechanisms

The distribution of metals in globular clusters and in the stars of the bulge component of the Galaxy are reproduced by means of galactic halo chemical evolution models giving particular attention to the observed Z(N) relation. Following Hartwick's (1976) demonstration that chemical distributions of the type observed for population II stars can be theoretically reproduced if mass is temporarily removed from the star-forming regions, two alternative mass segregation mechanisms are proposed to account for this phenomenon: the first being derived from the different dynamical behavior of the gas and the stars, and the second from consideration of a star formation law conditioned by the ionization of early-type stars. Models based on simple schematizations of the phenomena to which the two mass segregation mechanisms give rise, as well as on an initial mass function allowing for high M/L ratios, are found to reproduce observational data for both metal abundances and mass distributions.