Old stellar populations. I. A spectroscopic comparison of galactic globular clusters, M 31 globular clusters, and elliptical galaxies.

Integrated 9 A-resolution spectra in the 4000-6300 A region are presented for 17 Galactic globular clusters and 19 M31 globular clusters. Indices for 11 molecular bands and lines and several broadband colors are compared between the M31 and galactic cluster systems, as well as with the nuclei of 170 E galaxies. H-beta and CN are noted to differ markedly among the three groups. It is suggested that the three old stellar populations presently examined must differ in one or more respects beyond mean metallicity. Several models are analyzed to account for the higher H-beta and CN in M31 globulars. Most models fail to yield the requisite simultaneous H-beta and CN enhancements, except perhaps those of younger age. Satellite UV flux measurements will eventually offer an important tool for discriminating between various possible warm star components.