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The first part of this thesis presents a review of colour-magnitude photometry of Galactic globular clusters. A survey has been made of recently-published colourmagnitude photometry of globular clusters, and a self-consistent distance scale established for these data, using the method of subdwarf matching to the observed main sequences. The distances thus derived have been combined with other published colour-magnitude data to infer cluster ages and horizontal branch magnitudes. The relationship between cluster horizontal branch magnitude and metallicity is dicussed. In Chapter 2, a review is made of the photometric applications of charge coupled devices, giving particular attention to the aquisition and analysis of crowded field CCD images within globular clusters. Digital photometric techniques are discussed, including analytic profile fitting to stellar images. The major experimental part of this thesis concerns observations of the globular cluster w Centauri. These observations, their subsequent reduction, and photometric analysis, are discussed in Chapter 3. This chapter also contains a discussion of previous work on this cluster, and highlights its extremely unusual nature. The significant discovery of geometrically varying stellar profiles in the programme CCD images, and the techniques for their analysis, are discussed. The colour-magnitude data from these observations are discussed in Chapter 4. The distance to the cluster is determined, and it is shown that there exists an intrinsic spread in colour upon the cluster main sequence. Theoretical isochrones are employed to show that this spread in colour is consistent with a main sequence metallicity distribution similar to that seen in more highly-evolved stars within the cluster. The age of the cluster is determined as 16 +3 Gyr, by comparison with theoretical isochrones. This result is consistent with recent determinations for other clusters, and supports the theory that the Galactic globular cluster system is essentially coeval. The cluster main sequence luminosity function has been constructed, and is compared with recent observations and theory. In Chapter 5, a preliminary colour-magnitude study of the SMC cluster Lindsay 11 is presented.

We perform N-body simulations of star clusters in time-dependant galactic potentials. Since the Milky Way was built up through mergers with dwarf galaxies, its globular cluster population is made up of clusters formed both during the initial collapse of the Galaxy and in dwarf galaxies that were later accreted. Throughout a dwarf Milky Way merger, dwarf galaxy clusters are subject to a changing galactic potential. We investigate how this changing galactic potential affects the evolution of a cluster's half-mass radius. In particular, we simulate clusters on circular orbits around a dwarf galaxy that either falls into the Milky Way or evaporates as it orbits the Milky Way. We find that the dynamical evolution of a star cluster is determined by whichever galaxy has the strongest tidal field at the position of the cluster. Thus, clusters entering the Milky Way undergo changes in size as the Milky Way tidal field becomes stronger and that of the dwarf diminishes. We find that ultimately accreted clusters become the same size as a cluster born in the Milky Way on the same orbit. The change in size for accreted clusters occurs on a short time-scale, comparable to 1-2 cluster half-mass relaxation times. Assuming their initial sizes are similar, clusters born in the Galaxy and those that are accreted cannot be separated based on their current size alone. / Thesis / Master of Science (MSc)

NGC 5986 is a poorly studied but relatively massive Galactic globular cluster that shares several physical and morphological characteristics with "iron-complex" clusters known to exhibit significant metallicity and heavy-element dispersions. In order to determine whether NGC 5986 joins the iron-complex cluster class, we investigated the chemical composition of 25 red giant branch and asymptotic giant branch cluster stars using high-resolution spectra obtained with the Magellan-M2FS instrument. Cluster membership was verified using a combination of radial velocity and [Fe/H] measurements, and we found the cluster to have a mean heliocentric radial velocity of +99.76 km s(-1) (sigma = 7.44 km s(-1)). We derived a mean metallicity of [Fe/H] = -1.54 dex (sigma = 0.08 dex), but the cluster's small dispersion in [Fe/H] and low [La/Eu] abundance preclude it from being an iron-complex cluster. NGC 5986 has <[Eu/Fe]> = +0.76 dex (sigma = 0.08 dex), which is among the highest ratios detected in a Galactic cluster, but the small [Eu/Fe] dispersion is puzzling because such high values near [Fe/H] similar to -1.5 are typically only found in dwarf galaxies exhibiting large [Eu/Fe] variations. NGC 5986 exhibits classical globular cluster characteristics, such as uniformly enhanced [alpha/Fe] ratios, a small dispersion in Fe-peak abundances, and (anti) correlated light-element variations. Similar to NGC 2808, we find evidence that NGC 5986 may host at least four to five populations with distinct light-element compositions, and the presence of a clear Mg-Al anticorrelation along with an Al-Si correlation suggests that the cluster gas experienced processing at temperatures. greater than or similar to 65-70 MK. However, the current data do not support burning temperatures exceeding similar to 100 MK. We find some evidence that the first-and second-generation stars in NGC 5986 may be fully spatially mixed, which could indicate that the cluster has lost a significant fraction of its original mass.

Photometric and spectroscopic analyses have shown that the Galactic bulge cluster Terzan 5 hosts several populations with different metallicities and ages that manifest as a double red horizontal branch (HB). A recent investigation of the massive bulge cluster NGC 6569 revealed a similar, though less extended, HB luminosity split, but little is known about the cluster's detailed chemical composition. Therefore, we have used high- resolution spectra from the Magellan-M2FS and VLT-FLAMES spectrographs to investigate the chemical compositions and radial velocity distributions of red giant branch and HB stars in NGC 6569. We found the cluster to have a mean heliocentric radial velocity of -48.8 km s(-1) (sigma = 5.3 km s(-1); 148 stars) and <[Fe/H]> = -0.87 dex (19 stars), but the cluster's 0.05 dex [Fe/H] dispersion precludes a significant metallicity spread. NGC 6569 exhibits light- and heavy-element distributions that are common among old bulge/inner Galaxy globular clusters, including clear (anti) correlations between [O/Fe], [Na/Fe], and [Al/Fe]. The light-element data suggest that NGC 6569 may be composed of at least two distinct populations, and the cluster's low <[La/Eu]> = -0.11 dex indicates significant pollution with r- process material. We confirm that both HBs contain cluster members, but metallicity and lightelement variations are largely ruled out as sources for the luminosity difference. However, He mass fraction differences as small as Delta Y similar to 0.02 cannot be ruled out and may be sufficient to reproduce the double HB.

The Fabry-Pérot interferometer (FPI) was investigated as a potential tool for determining stellar elemental abundances. The FPI is a tunable narrow-band filter that makes it possible to obtain hundreds of stellar spectra simultaneously without the overhead associated with other multi-object spectroscopy techniques. This thesis used simulations and previously acquired data to investigate the FPI and develop data reduction techniques. Using observations of a CaII spectral line, an algorithm was created for fitting a Voigt profile to the spectrum segments. The values for radial velocity & equivalent width were compared to the values found by the group who supplied the data and found to agree well for the radial velocity values but there was some definite scatter in the equivalent width. These differences are attributed to different placement of the continuum level in the spectra. This curve-fitting script was modified to allow the fitting of synthetic spectra to simulated data. In this way it was possible to investigate how precise the abundance determination will be using the Robert Stobie Spectrograph's FPI mode. Large simulations showed that it will be possible to determine abundances to uncertainties of ±0.1 dex. This is an excellent result and should mean that future work using the FPI will give the results desired for large-scale s-process elemental abundance determination in globular cluster stars.

The Fabry-Pérot interferometer (FPI) was investigated as a potential tool for determining stellar elemental abundances. The FPI is a tunable narrow-band filter that makes it possible to obtain hundreds of stellar spectra simultaneously without the overhead associated with other multi-object spectroscopy techniques. This thesis used simulations and previously acquired data to investigate the FPI and develop data reduction techniques. Using observations of a CaII spectral line, an algorithm was created for fitting a Voigt profile to the spectrum segments. The values for radial velocity & equivalent width were compared to the values found by the group who supplied the data and found to agree well for the radial velocity values but there was some definite scatter in the equivalent width. These differences are attributed to different placement of the continuum level in the spectra. This curve-fitting script was modified to allow the fitting of synthetic spectra to simulated data. In this way it was possible to investigate how precise the abundance determination will be using the Robert Stobie Spectrograph's FPI mode. Large simulations showed that it will be possible to determine abundances to uncertainties of ±0.1 dex. This is an excellent result and should mean that future work using the FPI will give the results desired for large-scale s-process elemental abundance determination in globular cluster stars.

A 67" x 104" area of the metal-rich globular cluster M71 was searched for variable stars using 73 CCD frames. Using mean B and V values a colour-magnitude diagram down to V ≈ 22 is constructed. Four variables were discovered, with two more stars classed as possible candidates for variability. Phase diagrams and real time light curves are presented for all variables. One variable blue straggler (or SX Phe star) has been discovered with a period of 0.d05181. Values for the mass depend on the pulsation mode assumed for this star - (0.90 ± 0.13)M. for the first overtone mode, and (1.57 ± 0.22)M. for the fundamental mode. A second variable, of similar period (0.d06053), but with a magnitude l.m75 below the main sequence turn off was also found but it may be a field star. Two candidate eclipsing binary systems were found. The most likely period of one is 0.d37244. This value, and the shape of the light curve, suggest it may be a W UMa type variable. Its position on the CMD suggests that it too may be a field star. No period was obtainable for the other candidate binary due to a lack of phase coverage. Further data is needed to confirm and strengthen these claims. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

This thesis aims to better constrain the high-mass end of the globular cluster system (GCS) mass - Halo mass relation. This relation between the total mass contained in the globular clusters in a galaxy and the mass of its dark matter halo has been found to be nearly linear. The measured mass ration between the mass of the GCS and the halo mass, defined as eta, has been found to be constant over a large range of galaxy masses, however there is comparatively less data for galaxies with dark matter halo masses >10^13 solar masses. This research analyzes the GCSs of a sample of eleven high-mass brightest cluster galaxies (BCGs) through the use of the photometry program DOLPHOT on Hubble Space Telescope (HST) images in the F814W filter. The mass of the galaxies' GCSs were calculated from their GC radial distributions, and the dark matter halo masses were determined from the known relationship between total stellar mass and halo mass for BCGs. This research utilizes a new standardization technique to calculate the size of the GCS based on the galaxy's virial radius. These GC and halo masses were then compared to determine eta at this high-mass end, which was found to be eta=(6.84+/- 1.47)\times10^-5. When adding the sample BCGs to a catalogue of 303 lower-mass galaxies a total value for eta was found to be eta=(2.99 +/- 0.06)\times10^-5, which is within the literature range for of eta, and is both slightly higher and has a reduced uncertainty compared to the value for the catalogue galaxies alone which was found to be eta=(2.87 +/- 0.11)\times10^-5. This consistency between the eta-values of high-mass and lower-mass galaxies implies that in order for these BCGs to have such massive GCSs, a large proportion of these GCs must be accreted from galaxy mergers at late redshift. / Thesis / Master of Science (MSc)