SPECTROPHOTOMETRY OF EARLY-TYPE SYSTEMS .1. A METALLICITY SEQUENCE OF GLOBULAR-CLUSTERS

Integrated light spectrophotometry of the cores of 13 Milky Way globular clusters spanning a range in metallicity from [Fe/H]=-2 to nearly solar is used to establish the variation of a number of absorption features and colors as a function of metallicity. Analysis of the line strengths shows that globular clusters form a three or possibly four parameter family. Abundance is the primary component, accounting for 92% or more of the total variance of the sample. The next most significant component is an enhancement of the Balmer lines, consistent with the generation of coalesced binaries in post-core-collapse clusters. An additional component due to CN, CH, and Ca variations is also detected. A smooth spectral sequence in metallicity is interpolated from the spectrophotometry, for use in spectral synthesis studies. The spectral sequence is extrapolated to [Fe/H]=+0.50 to facilitate comparison with giant elliptical galaxies.