SYNTHESIS OF THE INTEGRATED SPECTRUM OF METAL-RICH GLOBULAR-CLUSTERS USING THE HR DIAGRAM AND A STELLAR LIBRARY

An average integrated spectrum of the nearly-solar metallicity, globul ar clusters NGC 6528, NGC 6553 and NGC 6440 is synthesized in the rang e 3500 < X < 9750 Angstrom with a library of stellar spectra and const raints provided by the observed colour-magnitude diagram (CMD) of NGC 6553. In order to account for the CMD parts below the observational cu toff, we employ a power law mass function with slopes x = -0.5, 1.35 a nd 2.5. We conclude that the MS contribution amounts to approximate to 15% of the integrated light at 5870 Angstrom and this minor contribut ion makes the integrated spectrum basically insensitive to these z val ues. The dominant components are the Red Giant Branch and the Horizont al Branch with respectively approximate to 60% and approximate to 20% of the flux at lambda 5870 Angstrom. The residuals of the observed int egrated spectrum with respect to the model suggest that [Fe/H] is slig htly subsolar in these globular clusters, whereas [CNO/Fe] is slightly above the solar ratio.