2004MNRAS.350..710Z

Using evolutionary population synthesis, we present integrated spectral energy distributions and absorption-line indices defined by the Lick Observatory image dissector scanner (referred to as Lick/IDS) system, for an extensive set of instantaneous burst single stellar populations (SSPs). The ages of the SSPs are in the range 1 Gyr ≤τ≤ 19 Gyr and the metallicities are in the range -2.3 ≤[Fe/H]≤+0.2. Our models use the rapid single stellar evolution algorithm of Hurley, Pols and Tout for the stellar evolutionary tracks, the empirical and semi-empirical calibrated BaSeL-2.0 model of Lejeune, Cuisinier and Buser for the library of stellar spectra and the empirical fitting functions of Worthey, Faber, Gonzalez and Burstein for the Lick/IDS spectral absorption-feature indices.

Applying our synthetic Lick/IDS absorption-line indices to the merit function, we obtain the age and the metallicity of the central region of M32, which can be well explained by an instantaneous SSP with an age of ∼6.5 Gyr and a metallicity similar to solar. Applying the derived age and the metallicity from the merit function to a number of index-index diagrams, we find that the plots of H_β-Fe5015 and H_β-Fe5782 are the best index-index diagrams from which we can directly obtain reasonable age and metallicity.