Binaries, galactic chemical evolution and the puzzling temporal evolution of 14N in the solar neighbourhood

Low metallicity very massive stars with an initial mass between 140 M-circle dot and 260 M-circle dot can be subdivided into two groups: those between 140 M-circle dot and 200 M-circle dot which produce a relatively small amount of Fe, and those with a mass between 200 M-circle dot and 260 M-circle dot where the Fe-yield ejected during the supernova explosion is enormous. We first demonstrate that the inclusion of the second group into a chemical evolutionary model for the Solar Neighbourhood predicts an early temporal evolution of Fe which is at variance with observations whereas it cannot be excluded that the first group could have been present. We then show that a low metallicity binary with very massive components (with a mass corresponding to the first group) can be an efficient site of primary N-14 production through the explosion of a binary component that has been polluted by the pair instability supernova ejecta of its companion. When we implement these massive binary N-14 yields in a chemical evolution model, we conclude that very massive close binaries may be important sites of N-14 enrichment during the early evolution of the Galaxy. (C) 2010 Elsevier B.V. All rights reserved.