High-resolution CCD spectra of stars in globular clusters. V - Carbon, nitrogen, and oxygen abundances in stars in 47 Tuc, M4, and M22

Abstract

Results are reported from blue, red, and IR observations of 15 selected stars in 47 Tuc, M4, and M22, obtained at resolution 20,000 and SNR 60-160 using a CCD array, Schmidt camera, and echelle spectrograph on the 4-m telescope at CTIO during 1987-1989. The data are presented in tables and graphs and analyzed to determine the abundances of C, N, O, and Fe. The Fe/H and O/Fe ratios are found to be -0.85 to -0.9 and 0.43 + or - 0.07 for 47 Tuc, -1.3 and 0.31 + or - 0.06 for M4, and -1.59 and 0.35 or less, respectively. The implications for models of stellar chemical evolution are discussed.