X-ray diversity in old star clusters

The X-ray sky is host to a variety of objects with very distinct properties and underlying physics. In particular, groups of stars known as star clusters are excellent environments to study an array of X-ray sources. In this thesis, I discuss the properties of low-luminosity X-ray sources in old star clusters from two distinct standpoints – the properties of faint X-ray sources within old open clusters, and the cooling of accretion-heated neutron-star crusts in low-mass X-ray binary (LMXB) systems in globular clusters.
The first part of the thesis focuses on the properties of close, interacting binary star populations in old open clusters. These properties are a powerful diagnostic of the stellar dynamics taking place inside the cluster. I used X-ray and optical telescope data to unravel the nature of such sources. I determined the total X-ray luminosity per unit mass of the cluster and found that the results support earlier findings that old open clusters are more luminous in X-rays than other old stellar populations.
In the second part of the thesis, I studied the cooling of accretion-heated neutron-star crusts in two LMXBs. Using X-ray monitoring observations of the neutron stars during quiescence, I followed the cooling of the crusts over time. Such studies of the thermal evolution of an accretion-heated neutron-star crust help in improving our understanding of the structure and composition of the crust, and how the thermal conductivities of different neutron stars vary under different physical conditions.