No description available.

Thesis (Ph. D.)--Lehigh University, 2005. / Includes vita. Includes bibliographical references (leaves 146-152).

Thesis (Ph. D.)--Lehigh University, 2005. / Includes vita. Includes bibliographical references (leaves 114-124).

No description available.

No description available.

Not available / text

The globular cluster system (GCS) of the elliptical galaxy NGC 4649 has been examined using the Gemini Multi-Object Spectrograph (GMOS); spectra for 156 candidate globular clusters (GCs) were obtained, extending to a galactocentric radius of 42 kpc. The system was found to have an even 78 GC candidates per population, using a colour of g-i = 0.92 (Faifer et al. 2011) to split the system into sub-populations. The populations refer to their metalicity; a g-i<0.92 is considered metal-poor (MP), and a g-i>0.92 is metal-rich (MR). Line-of-sight-velocity measurements and subsequent modelling, were used to measure the full GCS rotational velocity as 59+/-28 km/s, with a position angle of 218+/-28 degrees. The MR population was found to have rotational velocity of 81+/-42 km/s with a position angle of 221+/-29 degrees, while the MP population measures a rotational velocity of 30+/-36 km/s with a position angle of 202+/-73 degrees. The average velocity dispersion for the full GCS was calculated at 247+/-61 km/s, the MR population 266+/-94 km/s, and the MP population, 221+/-76 km/s. These findings are consistent (within uncertainties) with previous studies by Hwang et al.(2008), and Bridges et al. (2006). The velocity dispersion profile for all populations is constant with increasing radius, suggesting the presence of a dark matter (DM) halo. A tracer mass estimator was used to measure the mass at 42 kpc as (2.01+/-0.05)X10^{12} solar masses, for an isothermal potential, and (1.21+/-0.05)X10^{12} solar masses if the tracers followed the DM profile. Finally, it was estimated that M/L_{B}=22 - 44, consistent with the presence of considerable amounts of DM for a luminous galaxy. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2011-10-03 20:45:36.205

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.