Galactic Evolution of Carbon and Nitrogen

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Abstract

Abundance analysis of Carbon and Nitrogen has been performed in a sample of 32 late F and early G type dwarf metal poor stars in the metallicity range −3.3 < [Fe/H] < 0 using molecular lines of CH and NH in the near-UV. We find that [C/Fe] decreases slowly with increasing [Fe/H] while [N/Fe] remains flat. Furthermore we derived uniform and accurate C/O and N/O ratios using oxygen abundances from near-UV OH lines employed in our previous studies. We confirm the metallicity dependence of C/O ratio known from previous studies and caused by the metallicity dependence of the C yields from massive stars with mass loss. [C/O] does not remain constant below [O/H]=−0.5 but increases again with a large scatter. We find that a primary component is required in order explain the observations of N/O and that the N production history is similar in our Galaxy and DLAs.