We have derived a new Hβ absorption index definition, which is fully optimized as an age indicator for old and intermediate-aged stellar populations. Rather than using stellar spectra, we employed theoretical SEDs at moderately high resolution for simple stellar populations of different ages and metallicities. The new index, which is virtually insensitive to metallicity, provides us with improved abilities for lifting the age-metallicity degeneracy, that affects the standard Hβ Lick/IDS index definition. Among other advantages this new index does not require spectra of extremely high signal-to-noise and it can be easily applied to observations of faint galaxies or surveys data.
