An X-ray census of the youngest galactic star clusters

摘要

Stellar clusters are vitally important laboratories for astrophysical research. These clusters, some of which have populations numbering in the hundreds of thousands, comprise a coeval stellar population of similar chemical composition at the same distance, the analysis of which can confront stellar evolution theory as well as offering insights into the distribution of stellar masses in the Galaxy, the so called Initial Mass Function. Additionally, these clusters are the engines by which material in the Universe is recycled through the evolution and destruction of massive stars which redistribute material throughout a region via a cluster wind. This is a process best observed at X-ray wavelengths due to the temperature of the winds, however the actual strength of a cluster wind can be masked by apparent diffuse emission from unresolved sources in the region. In this Ph.D. project I have investigated this issue by characterising the X-ray emission from the youngest Galactic star clusters and quantifying the strength of the relative contributions to the observed diffuse emission. These observational results were found to be in agreement with theoretical models in the literature. Additionally, this analysis provided a wealth of information on the various cluster sub-populations as well as the clusters as a whole. Trends in the properties of the sub-populations with cluster age were investigated verifying previous observational results from the literature as well as demonstrating new trends, such as the frequency of magnetic wind sources in the youngest clusters. Supplementary to these analyses, the universality of the Initial Mass Function was probed in these clusters using the distribution of X-ray luminosities in a population known as the X-ray Luminosity Function. This was achieved by comparing the derived cluster X-ray Luminosity Functions to a well known and surveyed stellar population. It was found that the shape of the X-ray Luminosity Function of the clusters were generally consistent with that of the calibration cluster implying a similar underlying Initial Mass Function