Properties of Star Clusters

Star clusters are tracers of both stellar and Galactic evolution. As such it is essential to analyse their properties and distribution in the Galaxy. Ideally clusters’ fundamental properties (distance, reddening, age, metallicity) should be derived homogeneously, so that their uncertainties are systematic and any global trends identified can be trusted. With the increase

of newly discovered, purely photometric, large cluster samples from infrared surveys such

as 2MASS, WISE, UKIDSS-GPS and VISTA-VVV, new methods to reliably derive these

properties are required.

This Thesis presents novel methods to homogeneously derive the distances, extinctions, ages

and scale height measurements of cluster samples. Distances and extinctions are derived from

photometry alone, without the use of isochrone fitting, and cluster distances can be estimated

with a better than 40% accuracy. Cluster ages are derived using a pipeline which is designed

to consistently determine the values of clusters’ fundamental properties. Novel scale height

measurements are established with a 25% uncertainty for a sample size of 38. Using these methods, the FSR List cluster catalogue is found to be biased towards a distance of 3 kpc and modal age of 400 Myr. A dependence between the interstellar absorption value and Galactic longitude is found, characterised by AH (l)[mag/kpc] = 0.10+0.001 × |l?180 ? |/ ? for regions more than 60 ? from the Galactic Centre.

The temporal scale height evolution of clusters is accurately traced for the first time. A linear

relationship between cluster scale height and log(age/yr) is found which is significantly different from the stellar component of the Galactic Disk. There is also a weak age-independent trend between cluster scale height and Galactocentric distance. No significant temporal or spatial variations of the cluster distribution vertical zero point are found. The Sun’s vertical displacement from the Galactic Plane is measured to be Z? = 18.5 ± 1.2 pc.