We present a principal components analysis ( PCA ) of high-quality Lick/IDS absorption-line measurements for 11 indices in the wavelength range 4100–5400 Å for 39 Galactic globular clusters ( GCs ) .
Only the first principal component appears to be physically significant .
We find that there is a tight linear relationship between this first component ( PC1 ) and GC metallicity over a wide range in [ m/H ] ( -1.8 \leq [ m/H ] \leq 0 ) , suggesting that PC1 may be used to accurately estimate metallicities for old extragalactic GCs from their integrated spectra . Metallicity calibrations for other sets of indices in this wavelength range can be furnished upon request . The classic GC “ second parameter effect ” is noticeable in the Balmer indices , though it does not appear in our PCA .
We find little evidence for substantial differences in broad abundance patterns among Galactic GCs .
One implication is that the metal-poor and metal-rich GC subpopulations formed from very similar physical processes .