Exploring the Milky Way Outer Halo Globular Clusters AM 1 and Pyxis

Exploring the Milky Way Outer Halo Globular Clusters AM 1 and Pyxis Public Deposited

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Creator

Pohl, Brian
- Affiliation: College of Arts and Sciences, Department of Physics and Astronomy

Abstract

In order to probe the origins and history of the Milky Way halo, I executed a photometric survey of the outer halo globular clusters AM 1 and Pyxis using the southern astrophysical research (SOAR) telescope. The principal goal of this investigation was to determine the ages of these clusters, but the techniques employed in this process revealed other intrinsic properties such as chemical composition. A total of 32.2 hours of data were obtained on the program clusters, and observations of 22 stars from the Landolt (1992) catalogue were used to transform the clusters to the Johnson-Cousins BV standard system. The resultant color-magnitude diagrams are used in conjunction with the reference globular cluster M5 to determine the intrinsic properties of the program clusters. Three independent age determination techniques show agreement, consistent to within the error of the techniques, that AM 1 is -1.0 Gyr younger than, and that Pyxis is coeval to, the reference cluster M5. The chemical properties of both clusters are found to be the same for both clusters, [Fe/H] = -1.40 and [alpha/Fe] = +0.4, similar to M5. The results are presented in terms of two outstanding issues regarding the outer halo; the second parameter problem and the issue of accretion vs. in-situ formation.

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