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Nitrogen and oxygen as indicators of primordial enrichment
In this work the nitrogen abundances were derived for eight oldPopulation II stars, and the oxygen abundance was determined for two ofthese stars. A nitrogen overabundance is found for all stars. The Noverabundances in unevolved Population II stars indicate that the earlystars were probably more massive than the present ones and a partiallyprimary origin for 14N must be admitted. A massive PopulationIII is also required to explain the oxygen overabundances. One inferstwo possibilities, viz 500 M_sun; hypernovae or ordinarily massivestars are possible candidates for producing a considerable amount ofoxygen and primary nitrogen at early times. In order to have anagreement with the maximum mass of 100 M_sun; (Carlberg, 1981; Jones,1981), an IMF enhanced in ordinarily massive stars would be necessary.In this case, two variants are still possible: either the firstgeneration of stars consisted of massive stars only, or less massivestars did exist but did not evolve as far as to enrich the interstellarmedium until a later period.
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