Observations of 2.3-micron CO bands in 47 Tuc giants

The 2.3-micron CO bands of four 47 Tuc red giants have been observed with the AAT Fabry-Perot Infrared Grating Spectrometer with the goal of deriving carbon abundances as well as C-12/C-13 ratios. All four stars have (V-K) values between 3.42 and 3.52 (i.e., Teff = 3950 + or - 70 K), yet show substantial differences in their DDO C(41-42) colors, implying large variations in CN band strengths. Their CO colors also reveal an anticorrelation with CN band strength. The (C-13)O lines at 2.345 microns are seen in the present spectra of all four stars, although they are slightly stronger in the CN-strong/CO-weak stars. Simultaneous fits for (C/A) and C-12/C-13 in the observed spectra indicate that (C/A) is indeed lowest in the CN-strong stars. 51 refs