Carbon and nitrogen abundances in metal-poor stars.

Carbon and nitrogen abundances have been derived for 10 metal-poor stars. For each star, a combination of coarse and fine analyses have been used to determine a model atmosphere. Then, using the model and atomic- and molecular-line parameters in a spectrum-synthesis program, artificial CH, CN, and NH spectra have been computed. Finally, by comparing the synthetic and observed spectra, carbon and nitrogen abundances have been obtained. The principal results of the analysis are: (1) in metal-poor dwarfs [C/Fe] + 0.0; (2) all but one dwarf also show [N/Fe] +0.0; (3) metal-poor giants with log g < 2.4 appear to possess [C/N] < - 1.0, while those with higher gravities show [C/N] > +0.0. The anomalously low [C/N] values are interpreted here as effects of internal evolutions of the giant metal-poor stars. Finally, the consequences for galactic nucleosynthesis theories using the present results are discussed. Subject headings: abundances, stellar - late-type stars - nucleosynthesis - weak-line stars