Studies of the RR Lyrae Variables in the Galactic Field and Globular Clusters and the Morphology of the Horizontal Branch

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Dr. Zinn will measure the metal abundances and radial velocities of about 400 RR Lyrae variable stars. These data will improve our knowledge of the dependence of kinematics on metal abundance in the halo of our Galaxy and the populations of stars in the thick disk of the Galaxy. This will constrain models of the early evolution of the Galaxy. Two globular clusters, which are the most metal- rich clusters thought to contain RR Lyrae variables, will be observed. These data and computations of synthetic horizontal branch models will help resolve the enigma of the origin of the metal-rich RR Lyrae variables. Color magnitude diagrams will be constructed for about 10 globular clusters of stars close to the Galactic Center. These data will set an upper limit on the age variations that may be present, which in turn will constrain models of galactic evolution. The two most popular, and competing, pictures of the formation of the halo of our Galaxy predict very different relationships between the abundance ratio of iron to hydrogen and the mean rotational velocity about the Galactic Center. There is considerable debate whether the present data support either picture over the other. Dr. Zinn has designed an observational project which he expects will rule out one or the other of the two models.