A high cadence photometric survey of five southern hemisphere Milky Way globular clusters.
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
The Milky Way galaxy is surrounded by some 200 compact Globular Clusters (GCs) of stars, containing up to a million stars each. GCs are dynamical test beds for investigating and proving theories of stellar evolution and harbour a wide variety of binary type star systems and variable stars. Variables include RR Lyrae stars and other stellar exotica, such as blue stragglers, cataclysmic variables, and low-mass X-ray binaries. Recently, a potential new class of rapidly pulsating stars, hydrogen-rich subdwarf (sdO) pulsators, has been discovered in the ω Centauri GC. This research employed difference imaging algorithms to produce time-series photometry data from the 10m Southern African Large Telescope (SALT) and the European Southern Observatory 8.2m Very Large Telescope (VLT) and 3.58m New Technology Telescope (NTT) in La Silla, Chile to investigate the GCs: NGC 1904, NGC 2808, NGC 4833, NGC 5139 (ω Centauri), and NGC 6397. The following work was conducted: • a search for new discoveries in eclipsing binaries, contact binaries, BY Draconis stars, cataclysmic variables and other pulsating stars across all clusters; • generation of an updated set of Colour-Magnitude Diagrams (CMDs) to assist in classification of newly discovered variables; and • an analysis of the eclipsing binary stars and other variables. The result of this process was the discovery of 114 variable stars in NGC 5139, 19 of which were recovered from earlier surveys, leaving 95 potential new variable discoveries. This set includes 5 new eclipsing binary systems, 2 new short period EWs, 1 new low mass-ratio EW, 2 blue straggler stars and 2 RR Lyrae light curve shaped variables. For NGC 6397, 4 new variables are classified as BY Draconis stars associated with star spot activity and 1 potential eclipsing binary system was discovered.