GCPMWS · Globular Cluster Populations in the Milky Way Galaxy

Final Activity Report Summary - GCPMWS (Globular Cluster Populations in the Milky Way Galaxy)

Galaxies such as our own Milky Way are built up of billions of stars. These stars are distributed inside the galaxy in different ways. In our galaxy we find the oldest stars distributed in a spherical shape, the halo, whilst the younger and more numerous stars form a large disk. In the central parts of this disk we also find old stars. The amount of elements, such as iron and oxygen, which are present in the stars' atmospheres, varies as well. The old stars in the halo have the lowest abundances of such elements, while all stars in the disk and the central parts have much higher elemental abundances. Associated with these large stellar structures are the so-called globular clusters. These stellar clusters contain up to a million stars. The unique thing with a cluster is that, on average, all stars share the same composition of elemental abundances and have the same age. Since the stars are so concentrated in a globular cluster, the cluster is visible at large cosmic distances and we can readily observe globular clusters which are located in other galaxies very far away. The reasons for studying the globular clusters in the Milky Way were thus two-fold. The first was that we had a unique set of stars that shared exactly the same origin. This made possible to test our theories of stellar evolution by comparing the model prediction to the actual stars which were observed in the cluster. The second reason was that we could use the globular clusters in other galaxies to get information about their structure and evolution through studying of the clusters' properties. In addition, we could compare the light from the Milky Way clusters with the light which was emitted by whole galaxies and infer something about the amount of elements and the age of the whole underlying stellar populations that were present within them. These were some of the most important reasons for studying the Milky Way globular clusters in detail. Our work concentrated on the metal-rich globular clusters. These clusters were challenging to observe and had therefore not been studied in the same detail as the clusters which contained less elements. More specifically, we studied a rather unique cluster called NGC5927. This was most certainly associated with the stellar disk and gave a very good opportunity to find out if the underlying stellar populations, the stellar disk in this case, could indeed be accurately represented by their globular clusters.

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