Modelling chemical abundance anticorrelations on globular cluster
  spectra
  It is widely accepted that individual Galactic globular clusters harbor two
coeval generations of stars, the first one born with the `standard'
alpha-enhanced metal mixture observed in field Halo objects, the second one
characterized by an anticorrelated CN-ONa abundance pattern overimposed on the
first generation, alpha-enhanced metal mixture. We have investigated with
appropriate stellar population synthesis models how this second generation of
stars affects the integrated spectrum of a typical metal rich Galactic globular
cluster, like 47Tuc. Our main conclusions are: 1) the age-sensitive Balmer
line, Fe line and the [MgFe] indices widely used to determine age, Fe and total
metallicity of extragalactic systems are largely insensitive to the second
generation population; 2) enhanced He in second generation stars affects the
Balmer line indices of the integrated spectra, through the change of the turn
off temperature and the horizontal branch morphology of the underlying
isochrones, which translate into a bias towards slightly younger ages.
