Carbon and nitrogen abundances in metal-poor dwarfs of the solar neighborhood

Abstract

The authors have analyzed spectra of 83 subdwarfs for C, N, and Fe abundances. They deduced [C/Fe] from the CH bands (λ ≡ 4300 Å), [N/Fe] from the NH bands (λ ≡ 3360 Å), and [Fe/H] from strong mostly Fe I features (3400 Å ≤ λ ≤3550 Å). They find excellent agreement between the [Fe/H] values and the results obtained by other investigators based on high-resolution spectra. They find [C/Fe] to be essentially constant, with a scatter of σ ≡ 0.18 dex, over the range -0.75 ≥ [Fe/H] > -2.5, confirming that C is a primary nucleosynthetic species in this metallicity domain. It is found that the behavior of <[N/Fe]> as [Fe/H] declines is compatible with the assumption of a primary, as opposed to a secondary, origin of N, but the limiting value of <[N/Fe]> is found to be several tenths dex smaller than in previous investigations.