RR Lyrae in the Large Magellanic Cloud: New Insights Into Oosterhoff Intermediate Globular Clusters
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Date
2013
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Abstract
Current models suggest that the Milky Way halo was formed through the accretion of objects similar to the present day nearby dwarf galaxies. The ancient nature of RR Lyrae stars make them ideal tracers of stellar populations that can be used to determine how similar the present day dwarf galaxies are to the objects that were accreted to form the Milky Way halo. Globular clusters in the halo can be divided into two groups based on the properties of their RR Lyrae stars, called Oosterhoff groups, with a zone of avoidance between these groups. Nearby dwarf galaxies and their globular clusters fall not only in the Oosterhoff I and II groups, like in the Milky Way, but also in the zone of avoidance between these groups. These Oosterhoff intermediate objects, as the objects that fall in the zone of avoidance are called, present a challenge to the current theories of Milky Way halo formation. We present results of a recent study of globular clusters in the Large Magellanic Cloud which focused on the behavior of individual RR Lyrae stars in Oosterhoff intermediate objects and how this behavior compares to RR Lyrae stars in the other Oosterhoff groups. We discuss how these results demonstrate that Oosterhoff intermediate objects should not be thought of as one homogenous group. We also discuss how these results suggest that the traditional dividing lines between the Oosterhoff groups may need to be revised....