The spectroscopic age of 47 Tucanae

High signal-to-noise ratio integrated spectra of the metal-rich globular cluster 47 Tuc, spanning the Hγ_HR and Fe 4668 line indices, have been obtained. Jones & Worthey have suggested that the combination of these indices is the best available mechanism for cleanly separating the age-metallicity degeneracy that hampers the dating of distant, unresolved, elliptical galaxies. For the first time, we apply this technique to a nearby spheroidal system, 47 Tuc, for which independent ages, based upon more established methods, exist. Such an independent test of the technique's suitability has not been attempted before but is essential before the technique's application to more distant, unresolved, stellar populations can be considered valid. Because of its weak series of Balmer lines relative to model spectra, our results imply a spectroscopic age of 47 Tuc well in excess of 20 Gyr, which is at odds with the color-magnitude diagram age of 14 ± 1 Gyr. The derived metal abundance, however, is consistent with the known value. Although the observational constraints are restrictive, existing data cannot entirely exclude emission "fill-in" of the Hγ line as the source of the discrepancy.