Stellar Populations in the Nuclei of Galaxies.

The stellar contents of the nuclei of galaxies have been investigated by means of integrated spectra of some 32 extragalactic systems. All types of galaxies are represented, with special emphasis being placed on types E and Sb. Spectrograms of dispersion 200-850 A/mm taken over the interval XX 4000-6800 were analyzed, and in several galaxies a fairly unique solution for an abbreviated stellar population model was possible. Luminosity and temperature criteria in the green, yellow, and red regions of the spectrum were established empirically for late-type standard stars and were applied toward a two-dimensional classification of the galaxian spectra. The main luminosity criteria were the absolute strengths of the sodium D lines and the Mg l b triplet XX 5167-84. It was possible to separate the galaxies of the "K-nuclei" type into an approximately equal number of systems showing either giant or dwarf luminosity characteristics in the yellow and red In M31, M81, NGC 4594, and NGC 3379, for example, an appreciable fraction of the yellow and red light must originate in late K- and early M-type dwarfs. From the strengths of some strong absorption features in the blue and yellow regions of the M31 spectrum, a rough three-population model which satisfies the available multicolor observations was constructed. In this case the stellar luminosity function is greatly dwarf-enriched compared with the van Rhijn function. The spectra of the K-nuclei galaxies do not show metallic line weakening; i.e ,in the K-nuclei observed, pure population II stars do not dominate. A correlation between the spectral luminosity characteristics of the K-nuclei galaxies and their total luminosities and masses is suggested by the available data. In the Virgo and Coma clusters and in the M81 and Local Groups, the brightest galaxies all show moderate to strong D4ine absorption. The more massive galaxies have the strongest dwarf luminosity characteristics.