Principal component analysis for spectral indices of stellar populations

We apply the method of principal component analysis to a sample of simple stellar populations to select some age-sensitive spectral indices. Besides the well-known age-sensitive index, H B, we find that some other spectral indices have great potential to determine the age of stellar populations, such as G4300, Fe4383, C24668, and Mgb. In addition, we find that the sensitivity to age of these spectral indices depends on the metallicity of the simple stellar population (SSP): H B and G4300 are more suited to determine the age of the low-metallicity stellar population, C24668 and Mgb are more suited to the high-metallicity stellar population. The results suggest that the principal component analysis method provides a more objective and informative alternative to diagnostics by individual spectral lines.