CHEMICAL EVOLUTION OF PRIMARY ELEMENTS IN THE GALACTIC DISC - AN ANALYTICAL MODEL

We model the evolution of abundances of oxygen, iron, alpha and r-process elements in the Galactic disc using the instantaneous and delayed production approximations which enable the problem to be handled analytically. In addition to using the new greatly improved data published by Edvardsson et al. and the oxygen abundance distribution function of G dwarfs in the solar neighbourhood as improved by Sommer-Larsen, we take into account new survey data on metal-deficient stars which show that the thick-disc population extends to arbitrarily low metallicities, meaning that a significant proportion of stars previously classified as belonging to the halo, on grounds of low metallicity, actually belong to the disc and should be modelled as such, without bringing in any prior phase associated with the halo. Comparison with theoretical yields from Type II and Type Ia supernovae shows good agreement, as has previously been found by Tsujimoto et al. using a different approach.