The effect of increasing helium content and disk dwarfs evolution on the chemical enrichment of the Galaxy

The paper deals with two main effects: First the empirical metal abundance distribution in Main Sequence disk dwarfs of the solar neighborhood, and second, the theoretical possibility of (a) increased helium content as the Galaxy evolves, and (b) the presence of evolutionary effects in disk dwarfs. A linear increase of helium content with metal content is taken into account, and some constraints are imposed relative to initial, solar and present day observed values of Y and Z, and to observed relative helium to heavy element enrichment, Delta Y/Delta Z. 'Evolved' and 'unevolved' theoretical metal abundance distributions are derived by accounting for a two-phase model of chemical evolution of galaxies and for a linear mass dependence of star lifetimes in the spectral range G2V-G8V, and are compared with the empirical distribution. Finally, models of chemical evolution invoking homogeneous collapse without infall and inhomogeneous collapse with infall, are briefly discussed relative to the empirical metal abundance distribution in Main Sequence disk dwarfs of the solar neighborhood.