CARBON AND NITROGEN ABUNDANCES IN EXTREMELY METAL-DEFICIENT RED GIANTS.

The relative carbon and nitrogen abundances of a sample of metal-poor halo giants are analyzed with respect to their similarity with the abundances of similar stars in globular clusters. Spectra of 64 giants selected from the objective prism survey of Bond (1980) were obtained at a resolution of 8 A in the spectral region 3100-5300 A. C/Fe and N/Fe abundance ratios were estimated from the spectra by the method of spectrum synthesis using metallicities estimated from H and K line strengths. Halo giants with metallicities greater than or equal to -2.0, which are characteristic of giants in the M3 and M13 clusters, are found to have C/Fe and N/Fe abundance distributions similar to those of M3 but not M13, for which a greater carbon depletion and nitrogen enhancement is observed. Halo giants with metallicities less than -2.0 showed less carbon depletion and nitrogen enhancement than the corresponding M29 stars. Globular cluster and field halo stars with the same metallicities thus do not appear to be derived from the same parent population.