Carbon isotopic ratios in giant stars in the globular clusters M4 and M22

The abundances of C-12 and C-13 have been determined for seven stars in the globular cluster M4 and five stars in M22. The analysis utilizes low-resolution IR spectra, obtained with the KPNO-FTS, of the first-overtone vibration-rotation (V-R) bands of CO near a wavelength of 2.3 microns. This resolution is sufficient to resolve the individual V-R bands of C-12O and C-13O. Spectrum synthesis was used to derive individual carbon-12 and -13 abundances. This method of using low-resoluion spectra to obtain abundances was tested by deriving C-isotopic abundances in ten G and K giants that have been studied at high resolution by previous investigators: good agreement is found between the low- and high-resolution analyses. The globular cluster giants, in general, exhibit very low C-12/C-13 ratios, with most having C-12/C-13 of less than 10. Results suggest that those low-mass, low-metallicity giants have undergone extensive mixing of CN-processed material into their atmospheres. These results are compared to previous analyses of both metal-poor field giants and globular cluster giants, and discussed in terms of deep mixing in these stars. 40 refs