Carbon and nitrogen abundances in F- and G-type stars

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Abstract
Carbon and nitrogen abundances have been obtained for a sample of 11 F- and G-type dwarfs covering a range in [Fe/H] from −0.8 to +0.3. Model atmospheres, which included the effects of convection and line blanketing, were used to calculate synthetic spectra of the CH, CN and NH molecular bands. Effective oscillator strengths for the bands studied were found by matching synthetic spectra calculated from a model solar atmosphere with the observed solar bands; this was done at the same resolution as was obtained from the stellar coude spectra. Many of the metal-poor stars, and particularly the high velocity stars, were found to have substantial nitrogen over-deficiencies, suggesting that N is manufactured mostly in a secondary manner. The carbon-to-iron ratios were similar to the solar ratio, although there may be slight C over-deficiencies in metal-poor stars. However, the variation in C/Fe is not as marked as that found recently by Hearnshaw. A comprehensive discussion of the theoretical errors is given, and some applications to Galactic evolution are noted.

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