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

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2. THE OLDEST POPULATIONS OF THE MAGELLANIC CLOUDS

2.1. Definition and Nomenclature

The population that we are interested in describing here should more rightly be called the oldest observable population or the first substantial population in the Large and Small Magellanic Clouds (we use MC when referring to both Clouds). If there were a small tail of stars more metal poor than [Fe/H] = -3.0 in the MCs, therefore presumably older than the first major population, it would be impossible to detect it given currently available sample sizes, just as stars in the Milky Way halo with [Fe/H] < -3.0 have only been found by heroic efforts to search large numbers of Galactic halo stars (e.g. Beers et al 1992). We do not call the oldest major population in the MC "Population II" or the "halo population," as these words have connotations of abundance, age, and kinematics that may be inappropriate for the oldest MC populations. The word "halo" is used when these connotations are intended.

In this section we concentrate on describing the properties of the oldest population, including the mean age and kinematics. It is important to determine with certainty whether this "ancient" population exists in either Cloud or if the first dominant population is demonstrably younger in those galaxies than in the Milky Way. By an ancient population we mean a population coeval with the oldest globular clusters in the Milky Way, currently believed to be ~ 15 Gyr old. We acknowledge that the age scale may change in the future, but we believe that the age ranking of populations within the two Magellanic Clouds and relative to the Milky Way globulars will remain secure.

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