High signal-to-noise integrated spectra of the metal-rich globular cluster 47 Tuc , spanning the H _ { \gamma _ { HR } } and Fe4668 line indices , have been obtained .
The combination of these indices has been suggested ( Jones & Worthey 1995 , ApJ , 446 , L31 ) as the best available mechanism for cleanly separating the age-metallicity degeneracy which 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 an essential one before its 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 ” for 47 Tuc well in excess of 20 Gyr , at odds with the colour-magnitude diagram age of 14 \pm 1 Gyr .
The derived metal abundance , however , is consistent with the known value .
Emission “ fill-in ” of the H _ { \gamma } line as the source of the discrepancy can not be entirely excluded by existing data , although the observational constraints are restrictive .