A principal component analysis of the equivalent widths of spectral lines of star clusters

Using principal component analysis, we have studied the equivalent widths of optical spectral lines of 41 Galactic globular clusters and 22 young stellar clusters. We have discovered that some characteristic spectral lines, such as the CN, Ca IIK, Ca IIH and MgI+MgII lines, are rather sensitive to metallicity. We have also found some lines that may be used as indicators of age, e.g. Hδ, Hγ, Hβ and Hα. These lines can help us to disentangle the coupling effects of age and metallicity in the clusters.