Annu. Rev. Astron. Astrophys. 1996. 34: 511-550
Copyright © 1996 by . All rights reserved

Reprinted with kind permission from , 4139 El Camino Way, Palo Alto, California, USA

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OLD AND INTERMEDIATE-AGE STELLAR POPULATIONS IN THE MAGELLANIC CLOUDS

Edward W. Olszewski


Steward Observatory, University of Arizona, Tucson, Arizona 85721-0065

Nicholas B. Suntzeff


Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatories, Casilla La Serena, 603, Chile

Mario Mateo


Department of Astronomy, University of Michigan, 830 Dennison, Ann Arbor, Michigan 48109-1090


Abstract. The Magellanic Clouds have galactocentric distances of 50 and 63 kiloparsecs, making it possible to probe the older populations of clusters and stars in some detail. Although it is clear that both galaxies contain an old population, it is not yet certain whether this population is coeval with the date of formation of the oldest globulars in the Milky Way. The kinematics of this old population in the Large Magellanic Cloud (LMC) are surprising; no component of this old population is currently measured to be part of a hot halo supported by velocity dispersion. Spectroscopy of field stars is beginning to show the existence of a small population of stars with abundances [Fe/H] less than -1.4. These stars will help to unravel the star-formation history when the next generation of telescopes are commissioned. Asymptotic giant branch stars, long-period variables, planetary nebulae, and horizontal-branch clump stars can be used to trace the extent and kinematics of the intermediate-age population. Deep color-magnitude diagrams can be used to derive the relative proportions of stars older than 1 Gyr. The age distribution of populous clusters and the age-metallicity relation are used to compare the evolution of the two Magellanic Clouds to each other. The issue of where the LMC's metals originated is explored, as is the question of what triggers star formation in the Clouds.


Table of Contents

INTRODUCTION

THE OLDEST POPULATIONS OF THE MAGELLANIC CLOUDS
Definition and Nomenclature
The Old Cluster Population
Age of the Oldest Clusters
Kinematics of the Oldest Clusters
The Field RR Lyraes
The Old Long-Period Variables
The Old and Metal-Poor Field Stars
The CH Stars

THE INTERMEDIATE-AGE POPULATIONS OF THE MAGELLANIC CLOUDS
Definitions
Evolved Field Stars
Main-Sequence Stars
Intermediate-Age Clusters
What Triggers Star Formation in the Magellanic Clouds?

WISH LIST

REFERENCES

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