THE STELLAR POPULATION OF THE GALACTIC NUCLEAR BULGE

Many years of'work by a number of investigators has shown that a case study of the resolved stars in the Galactic bulge can provide more detailed information about the characteristic stellar population found in elliptical galaxies and the bulges of spiral galaxies than can be deduced from analysis of the spectrum of the integrated light of unresolved external systems. Line strengths in the spectra of bulge giants show a considerable spread of metallicity. The dominant component is super metal rich. A minority fraction of the giants is mildly metal poor, as are the RR Lyrae variables. Spectral surveys have identified all the late M giants in several bulge areas. These giants show the IR features noted in studies of the integrated light of galaxies, but are neither as cool nor as luminous as local giants of the same spectral type. Broad-band colors of bulge giants indicate other differences relative to solar-neighborhood prototypes that have traditionally been used in modeling galaxy populations. More detailed characterization of the bulge stars is needed before undertaking a quantitative population model. The bulk of the evidence is in harmony with the Tinsley concept of an old population now simply aging, though the time for the star formation rate to sink essentially to zero may not have been as short as in the single-burst approximation.