Very massive close binaries and the puzzling temporal evolution of $^{14}N$ in the solar neighbourhood

D. Vanbeveren and E. De Donder

Astrophysical Institute, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium

Low metallicity very massive stars with an initial mass between 140 M$_{\odot}$ and
260 M$_{\odot}$ can be subdivided into two groups: those between 140 M$_{\odot}$ and 200
M$_{\odot}$ which produce a relatively small amount of Fe, and those with a mass between 200
M$_{\odot}$ and 260 M$_{\odot}$ 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 can not 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 $^{14}$N 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 $^{14}$N yields in a chemical evolution model, we conclude
that very massive close binaries may be important sites of $^{14}$N enrichment during the early
evolution of the Galaxy.

Reference: New Astronomy
Status: Manuscript has been accepted