TiO Continuum Placement Effects in 47 Tucanae Giants

High-resolution echelle SIT Vidicon spectra have been obtained of giants in the metal-rich globular cluster 47 Tuc. The sample includes the giants previously investigated with the echelle photographically by Pilachowski, Canterna, and Wallerstein (1980), and Cottrell and Da Costa (1981), who derived controversially low abundances. The new spectra show that all of these giants have TiO absorption present in the wavelength region of the previous studies, particularly the two very cool giants in the Pilachowski et al. sample. The TiO bands were not recognized in the photographic spectra because they extend over several orders, each of which was analyzed independently. The presence of TiO absorption indicates that the abundances derived by these previous investigations are underestimates because of the underestimation of the continuum. The underestimates are not large, however, amounting to 0.2 dex or less, but this is sufficient to bring the echelle abundances into good agreement with estimates based on recent lower resolution techniques. An abundance for 47 Tuc of Fe/H about -0.9, intermediate between the old and new scales, is indicated.