Modelling the evolution and nucleosynthesis of carbon-enhanced   metal-poor stars
  We present the results of binary population simulations of carbon-enhanced metal-poor (CEMP) stars. We show that nitrogen and fluorine are useful tracers of the origin of CEMP stars, and conclude that the observed paucity of very nitrogen-rich stars puts strong constraints on possible modifications of the initial mass function at low metallicity. The large number fraction of CEMP stars may instead require much more efficient dredge-up from low-metallicity asymptotic giant branch stars. 
O. R. Pols, R. G. Izzard, M. Lugaro, S. E. de Mink