The concept of Stellar Populations has played a fundamental role in astronomy in the last few decades. It was introduced by Walter Baade after he was able to resolve the Andromeda Nebula and its companions into stars when he used red-sensitive plates and realised that there were two fundamentally different Herzsprung-Russell diagrams in our and these nearby galaxies (common stars in the solar neighborhood versus globular clusters). This result was published in two papers in 1944 in volume 100 of the Astrophysical Journal. Subsequent research gave the concept a much firmer basis and at the famous Vatican Symposium of 1957 resulted in a general scheme of the concept and a working hypothesis for idea's on the formation and evolution of the Galaxy. This has been a guiding principle of studies of our and other galaxies for decades. Some years ago it seemed to us appropriate to commemorate Baade's seminal work in 1994, when it would have its 50-th anniversary, and to review its present status and also its role in contempory understanding. While we were in Leiden for an administrative committee, we discussed the matter again and over beers on October 29, 1991 we decided the take the initiative for an IAU Symposium on the subject during the 1994 IAU General Assembly in Den Haag, the Netherlands.

Inhalt

Preface. History of the Concept of Stellar Populations. Report on the Progress in Stellar Evolution to 1950; O. Gingerich. Walter Baade's Discovery of the Two Stellar Populations; D. E. Osterbrock. The Discovery of the Chemical Composition-Kinematics Connection in the 1950s; N. G. Roman. Stellar Evolution and the Population Concept after 1950; The Vatican Conference; A. Blaauw. Globular Cluster Systems. The Galactic Globular Cluster System; J. E. Husser. The Stellar Population of a Typical Globular Cluster; F. Fusi Pecci and G. Clementini. Stars in the Galactic Halo; T. D. Kinman. Globular Cluster Systems in Other Galaxies; W. E. Harris. Open Clusters and the Galactic Disk. Evolution of the Galactic Halo and Disk; G. Gilmore. Age and Metallicity Distributions among Galactic Disk Stars; P. E. Nissen. Early-Type Stars; K. C. Freeman. High Velocity Clouds in the Galaxy; F.J. Lockman. Chemical Evolution of the Galactic Disk and Bulge; R. F. G. Wyse. Stellar Populations in Local Group Galaxies. Stellar Populations in the Magellanic Clouds; M. W. Feast. M31 and Companions: A Key to Baade's Stellar Populations Then and Now; W. L. Freedman. The Stellar Populations in Local Group Dwarf Galaxies; A. Saha. Star Clusters in Local Group Galaxies; E. W. Olszewski. Dark Matter in Galaxies. Dark Matter in the Milky Way; K. Kuijken. Dark Matter in Spiral Galaxies; P. C. van der Kruit. Central Black Holes and Dark Holes in Elliptical Galaxies; P. T. de Zeeuw. Dark Matter in Clusters of Galaxies; C. R. Canizares. Stellar Populations in Elliptical Galaxies. The UV Upturnin Elliptical Galaxies; H. G. Ferguson. The Stellar Ages of Elliptical Galaxies; S. M. Faber, S.C. Trager, J.J. Gonzalez, G. Worthey. Stellar Populations in S0 Galaxies; R. Bender, A. Paquet. Measuring the Evolution of the M/L Ratio from the Fundamental Plane; M. Franx. Effects of Late Mergers; F. Schweizer. Environmental Effects in the Stellar Populations of Elliptical Galaxies; J. R. Lucey. Galaxies at Large Red Shifts. The Morphological Evolution for Field Galaxies; R. S. Ellis. Stellar Populations at Large Redshifts; R. W. O'Connell. Galaxy Evolution from Deep Galaxy Counts; J. P. Gardner. Classification Schemes of Stellar Populations. Formation Models of Galaxies; S. D. M. White. Stellar Dating and Formation of Galactic Spheroids; A. Renzini. Panel Discussion on the Classification and Terminology of Stellar Populations; I. R. King. Conference Summary; J. Mould. Poster Papers. Index.