Nitrogen overbundances in population II dwarfs

From a survey and spectrum synthesis analysis of the NH features in the spectra of some 25 Population II dwarfs, two objects have been found in which nitrogen is overabundant relative to the heavy elements by a factor approx.50-100 (i.e., [N/Fe]approx.1.7-2.0). The two stars are HD 74000 and HD 160617, which are well-known, extremely metal-deficient subdwarfs with [Fe/H]approx.-2.0. Unless one is willing to invoke mixing during the main-sequence phase, or nitrogen-enhanced mass transfer in a binary system (both of which we believe unlikely explanations), the available data suggest a decoupling of nitrogen and heavy element production during the first stellar generations, and indicate that, in the early universe, nitrogen was produced as a primary element