OLD AND INTERMEDIATE-AGE STELLAR POPULATIONS IN THE MAGELLANIC CLOUDS

Abstract

▪ 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.