Understanding the formation and evolution of galaxies is one of the most active areas of research in astrophysics. Hierarchical merging of proto-galactic fragments to build more massive galaxies is the current preferred model. A key prediction of this theory is that haloes of nearby galaxies should contain remnants of this assembly process in the form of tidal debris. Found in all but the smallest of dwarf galaxies, globular clusters (GC) are excellent probes of galaxy haloes. Having high luminosities, they are favourable targets in the outer regions of galaxies where the associated stellar surface brightness is low. GCs are thought to be amongst the oldest stellar systems in the Universe, and are likely born in the most significant phases of galaxy formation. Their metallicities, ages, spatial distributions and kinematics can be used to constrain the assembly history of their host galaxy. In this thesis, I explore the photometric and kinematic properties of several GC systems in our cosmological backyard, the Local Group of galaxies. The work is based on a major spectroscopic campaign, follow-up to the photometric Pan- Andromeda Archaeological Survey (PAndAS), as well as additional optical and near-IR data sets. Radial velocities are obtained for 78 GCs in the halo ofM31, 63 of which had no previous spectroscopic information. The GCs have projected radii between ∼ 20 and 140 kpc, thus sampling the true outer halo of this galaxy. In addition, GCs in the dwarf galaxies NGC 147, NGC 185 and NGC 6822 are also spectroscopically observed. By conducting a detailed kinematic analysis, I find that GCs in the outer halo of M31 exhibit coherent rotation around the minor optical axis, in the same direction as their more centrally located counterparts, but with a smaller amplitude of 86 ± 17 km s−1. There is also evidence that the velocity dispersion of the outer halo GC system decreases as a function of projected radius from theM31 centre, and this relation can be well described by a power lawof index ≈ −0.5. I detect and discuss various velocity correlations amongst GCs that lie on stellar streams in the M31 halo. Simple Monte Carlo tests show that such configurations are unlikely to form by chance, implying that significant fraction of the GCs in the M31 halo have been accreted alongside their parent dwarf galaxies. I also estimate the dynamical mass of M31 within 200 kpc to be (1.2 − 1.6) ± 0.2 × 1012 M⊙. I also characterize the GC systems of three dwarf galaxies in the Local Group: the dwarf elliptical satellites of M31, NGC 147 and NGC 185, and the isolated dwarf irregular NGC 6822. Using uniform optical and near-IR photometry, I constrain the ages and metallicities of their constituent GCs. The metallicities of the GCs around NGC 147 and NGC 185 are found to be metal-poor ([Fe/H]. −1.25 dex), while their ages are more difficult to constrain. The GCs hosted by NGC 6822 are found to be old (>9 Gyr) and to have a spread of metallicities (−1.6 . [Fe/H] . −0.4). I find close similarity between the mean optical (V − I)0 colours of the GCs hosted by these three dwarf galaxies to those located in the M31 outer halo, consistent with the idea that dwarf galaxies akin to them might have contributed toward the assembly of the M31 outer halo GC population. Analysing their kinematics, I find no evidence for systemic rotation in either of these three GC systems. Finally, I use the available GC kinematic data to calculate the dynamical masses of NGC 147, NGC 185 and NGC 6822.

A thorough understanding of nucleosynthesis and element formation in stars of all evolutionary phases is of vital importance in stellar astrophysics. It provides information about internal structure, conditions and nuclear processes occurring in the stellar interior. The heavy elements formed in a star throughout its life are returned to the interstellar medium through mass loss processes. New populations of stars are then formed from this previously enriched material. This continues the cycle of element recycling in the Universe and has great consequence for galactic chemical evolution. As both modelling and observing techniques advance, more surveys are required to ensure there is agreement between the two. It is hoped that when a thorough understanding of the internal processes in giant stars is reached, the evolutionary models will reproduce the observed elemental yields. This work provides an internally self-consistent analysis of the element abundances produced via nucleosynthesis and s-process element formation occurring in giant stars in different stellar environments. High resolution spectroscopic observations have been taken of Asymptotic Giant Branch (AGB) and Red Giant Branch (RGB) stars in three different stellar environments. Spectrum synthesis has been used to determine s-process element abundances for RGB stars in the Hyades open cluster, RGB and AGB stars in the globular cluster, 47 Tucanae, and AGB stars in the galactic field. It was found that the two Hyades giant studied showed solar, or near-solar, abundances of s-process elements. Enhancements in the light s-process elements, Y and Zr, of +0.02 to +0.11 were observed, while enhancements in the heavy s-process elements, La, Pr and Nd, ranged from +0.06 to +0.16. These results are consistent with previous findings of enhancements in Y of ~+0.12, and of ~+0.15 for the heavy s-process elements. The results from 47 Tucanae suggest a genuine star-to-star scatter in the s-process element abundances in the giant stars of this globular cluster. This is unexpected due to the fact that stars in a globular cluster are thought to have the same formation and chemical history. However, spreads in s-process element abundances of as much as +-0.7 dex are observed between this study and three other studies of similar stars in the same cluster. A range of field stars along the AGB phase, ranging from M to MS to S to SC, have been analysed for s-process enrichment. The observed element abundances are compared with those predicted by recent modelling of the AGB phase of evolution. Enhancements in s-process element abundances range from [s/Fe]~0.00 for M stars, to ~+0.50 for MS stars, through to ~+0.95 for S stars. The comparison of these enhancements with those predicted by modelling provides an indication of the success of these models and will enable theoreticians to further refine their understanding of the internal nucleosynthetic processes present in giant stars.

The confirmation of a globular cluster (GC) in the recently discovered ultrafaint galaxy Eridanus II (Eri II) motivated us to examine the question posed in the title. After estimating the halo mass of Eri II using a published stellar mass-halo mass relation, the one GC in this galaxy supports extending the relationship between the number of GCs hosted by a galaxy and the galaxy's total mass about two orders of magnitude in stellar mass below the previous limit. For this empirically determined specific frequency of between 0.06 and 0.39 GCs per 10(9)M(circle dot) of total mass, the surviving Milky Way (MW) subhalos with masses smaller than 10(10)M(circle dot) could host as many as 5-31 GCs, broadly consistent with the actual population of outer halo MW GCs, although matching the radial distribution in detail remains a challenge. Using a subhalo mass function from published high-resolution numerical simulations and a Poissonian model for populating those halos with the aforementioned empirically constrained frequency, we find that about 90% of these GCs lie in lower-mass subhalos than that of Eri II. From what we know about the stellar mass-halo mass function, the subhalo mass function, and the mass-normalized GC specific frequency, we conclude that some of the MW's outer halo GCs are likely to be hosted by undetected subhalos with extremely modest stellar populations.

Over the last decade, 135 extrasolar planets have been discovered, the vast majority found by ongoing radial velocity searches. Of the stars sampled in these searches, 1% have `Hot Jupiter' planets associated with them. Having masses equivalent to Jupiter yet orbital periods of only a few days, this new class of planet is clearly unlike anything in our Solar System.¶ Hot Jupiters present us with an intriguing prospect. If the orientation of the planetary orbit is close to edge-on, the planet will periodically transit across the face of its star, resulting in a small drop in brightness. This transit phenomenon has been successfully used for planet detection over the last couple of years, allowing determination of the planetary radius and accurate mass estimates when coupled with radial velocity observations.¶ To aid understanding of the effect stellar environment plays on Hot Jupiter formation and survivability, this thesis presents the results of a wide-field search for transiting Hot Jupiters in the globular cluster 47 Tucanae. This cluster presents many thousands of stars in a moderate field of view and provides the perfect target for a search of this nature. One previous transit search has been made in the central core of 47 Tuc; using the HST for 8.3 continuous days, Gilliland et.al (2000) expected 17 transits yet found none. This null result suggests that either system metallicity or stellar density may be inhibiting Hot Jupiter formation or survivability in the cluster.¶ This thesis presents a search for transits with a field of view 250 times larger than the HST search and samples the uncrowded outer halo of the cluster (previously unsampled for transits), providing important constraints on the effect of environment on Hot Jupiter formation. If planets are found, then stellar density would seem responsible for the Gilliland et.al (2000) core null result. If no planets are found to a significant level, the survey would provide strong evidence that system metallicity is the dominant factor. Using the ANU 40'' (1m) telescope at Siding Spring Observatory, a 30.4 night observing run was executed and photometry was derived via differential imaging. The dataset numbers 109,000 cluster (and field) stars for photometric analysis, of which 22,000 are suitable for the transit search. With a custom-written transit detection algorithm and extensive Monte Carlo simulations to model the dataset, seven planets should be detectable if the occurrence rate of Hot Jupiters is the same in the cluster as in the Solar Neighbourhood.¶ Despite a detailed search, no transit signatures were identified. This result strongly indicates that the low metallicity of the cluster is the dominant factor inhibiting planet formation in 47 Tuc. Current results in the Solar Neighbourhood show that planet frequency is strongly biased towards stars of high metallicity. This thesis shows that the metallicity trend is likely a universal phenomenon, not only limited to the immediate Solar Neighbourhood and raises questions of whether planets were much rarer in the earlier Universe.¶ As a side result of the search, 100 variable stars were identified in the field, 69 of which are new discoveries. Subsequent analysis reveals a strong period segregation among the cluster eclipsing binaries, indicating previously unobserved dynamical effects in the cluster. Distance estimates for both 47 Tuc and the SMC are in agreement with previously published values and an independent identification of the binary period-colour relation was observed. Two binaries seem to have low-luminosity companions worthy of followup and one variable is likely a star in the early phases of planetary nebula formation. All of the results presented in this thesis have been published in three separately refereed research papers.

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Millisecond pulsars (MSP) are old neutron stars that have been spun up to high spin frequencies(as fast as 716 Hz) through the accretion of matter from a companion star. The extreme stellar densities in the core of globular clusters creates numerous accreting neutron star systems through exchange interactions; this leads to the formation of MSPs in larger numbers than in the galactic disk. Over the course of this project, we have collected over 17 TB of data on the 3 globular clusters M28, NGC6440 and NGC6441 plus 2 observations on NGC6522 and NGC6624 as part of the recently begun S-band survey using the Green Bank telescope. I have analyzed and conducted acceleration searches on 70% of the data and discovered 7 of the 23 new millisecond pulsars reported in this work. One year of timing observations of the pulsars in M28 and NGC6440 has led to the phase connected solution for 12 of the 15 new pulsars in those two clusters, 7 of which are in binaries. We have measured the rate of advance of periastron for two highly eccentric binaries and assuming this is purely due to general relativity, this leads to total system masses of (1.616 - 0.014)M and (2.2 - 0.8)M for M28C and NGC6440B respectively. The small mass function combined with this information imply that the most likely neutron star mass of NGC6440B is either very large or else there could be significant contribution to the advance of periastron from a nonzero quadrupole moment due to tidal interaction with the companion. Measurements of the period derivatives for many of the pulsars show that they are dominated by the dynamical effect of the gravitational field of the clusters. Finally, we have discovered the potential presence of a Mars-mass planet orbiting the pulsar NGC6440C with a period of 21 days. A dedicated timing campaign will be necessary to confirm the presence of such an object.

An introduction is given to the fields of X-ray and cataclysmic binaries, low mass X-ray binaries (LMXBs) and globular clusters. New observations of the W Vir star AC5 (=V86) are used show that it is probably the source of Hα emission previous authors have found in core of the globular cluster M15. The first phase resolved optical spectroscopy of AC211, the optical counterpart of the X-ray source in M15, are presented, and its binary period discovered to be 9.l±0.5 hours. A re-analysis of archive ultraviolet (UV) spectra of M15, shows spectral features which are attributed to AC211. These observations are combined with those of other authors, to prove AC211 is probably an "accretion disc corona" (ADC) source. After reviewing the superoutbursts of the SU UMa class of dwarf novae, X-ray, UV, optical and infrared observations of the SU UMa star OY Car are used to show that during superoutburst there is extensive vertical structure in its accretion disc, similar to that in the ADC and "dipping" LMXBs. Archive UV data from the 1978 outburst of WZ Sge shows that it had similar vertical structure. UV observations presented of EX Hya during a bright outburst may have the same explanation. From the OY Car data, a temperature and area for the region which produces the "superhump" light are derived, of 8 OOOK and ^-10²⁰cm², respectively. It is found that during OY Car's superoutburst, the size of the 0-C variations of the eclipse timings are significantly smaller than was previously thought, and that it has an extended X-ray source whose size is comparable to the binary separation. The results are discussed with respect to models of the superhump phenomena in SU UMa stars, and possible causes of vertical disc structure in X-ray and cataclysmic binaries.

Millisecond pulsars (MSP) are old neutron stars that have been spun up to high spin frequencies(as fast as 716 Hz) through the accretion of matter from a companion star. The extreme stellar densities in the core of globular clusters creates numerous accreting neutron star systems through exchange interactions; this leads to the formation of MSPs in larger numbers than in the galactic disk. Over the course of this project, we have collected over 17 TB of data on the 3 globular clusters M28, NGC6440 and NGC6441 plus 2 observations on NGC6522 and NGC6624 as part of the recently begun S-band survey using the Green Bank telescope. I have analyzed and conducted acceleration searches on 70% of the data and discovered 7 of the 23 new millisecond pulsars reported in this work. One year of timing observations of the pulsars in M28 and NGC6440 has led to the phase connected solution for 12 of the 15 new pulsars in those two clusters, 7 of which are in binaries. We have measured the rate of advance of periastron for two highly eccentric binaries and assuming this is purely due to general relativity, this leads to total system masses of (1.616 - 0.014)M and (2.2 - 0.8)M for M28C and NGC6440B respectively. The small mass function combined with this information imply that the most likely neutron star mass of NGC6440B is either very large or else there could be significant contribution to the advance of periastron from a nonzero quadrupole moment due to tidal interaction with the companion. Measurements of the period derivatives for many of the pulsars show that they are dominated by the dynamical effect of the gravitational field of the clusters. Finally, we have discovered the potential presence of a Mars-mass planet orbiting the pulsar NGC6440C with a period of 21 days. A dedicated timing campaign will be necessary to confirm the presence of such an object.

A thorough understanding of nucleosynthesis and element formation in stars of all evolutionary phases is of vital importance in stellar astrophysics. It provides information about internal structure, conditions and nuclear processes occurring in the stellar interior. The heavy elements formed in a star throughout its life are returned to the interstellar medium through mass loss processes. New populations of stars are then formed from this previously enriched material. This continues the cycle of element recycling in the Universe and has great consequence for galactic chemical evolution. As both modelling and observing techniques advance, more surveys are required to ensure there is agreement between the two. It is hoped that when a thorough understanding of the internal processes in giant stars is reached, the evolutionary models will reproduce the observed elemental yields. This work provides an internally self-consistent analysis of the element abundances produced via nucleosynthesis and s-process element formation occurring in giant stars in different stellar environments. High resolution spectroscopic observations have been taken of Asymptotic Giant Branch (AGB) and Red Giant Branch (RGB) stars in three different stellar environments. Spectrum synthesis has been used to determine s-process element abundances for RGB stars in the Hyades open cluster, RGB and AGB stars in the globular cluster, 47 Tucanae, and AGB stars in the galactic field. It was found that the two Hyades giant studied showed solar, or near-solar, abundances of s-process elements. Enhancements in the light s-process elements, Y and Zr, of +0.02 to +0.11 were observed, while enhancements in the heavy s-process elements, La, Pr and Nd, ranged from +0.06 to +0.16. These results are consistent with previous findings of enhancements in Y of ~+0.12, and of ~+0.15 for the heavy s-process elements. The results from 47 Tucanae suggest a genuine star-to-star scatter in the s-process element abundances in the giant stars of this globular cluster. This is unexpected due to the fact that stars in a globular cluster are thought to have the same formation and chemical history. However, spreads in s-process element abundances of as much as +-0.7 dex are observed between this study and three other studies of similar stars in the same cluster. A range of field stars along the AGB phase, ranging from M to MS to S to SC, have been analysed for s-process enrichment. The observed element abundances are compared with those predicted by recent modelling of the AGB phase of evolution. Enhancements in s-process element abundances range from [s/Fe]~0.00 for M stars, to ~+0.50 for MS stars, through to ~+0.95 for S stars. The comparison of these enhancements with those predicted by modelling provides an indication of the success of these models and will enable theoreticians to further refine their understanding of the internal nucleosynthetic processes present in giant stars.

This dissertation presents a detailed study of many aspects of the Horizontal Branch (HB) phase of stellar evolution. A classical technique of stellar structure analysis is summarized, and applied to Zero-Age Horizontal Branch (ZAHB) models. The chief conclusions from this work are firstly, that the total mass of the envelope sensitively affects the luminosity of the hydrogen-burning shell and the equilibrium of the helium-rich core. Secondly, the rapid progression of models across the Hertzsprung-Russell diagram with decreasing mass is the result of important changes in the hydrostatic structure of the stars. Thirdly, the luminosity-metallicity relationship of the Zero Age models results from the change in the core equilibrium luminosity with the CNO abundance of the shell region, together with the decrease in stellar mass at fixed effective temperature. The change in the mass-temperature relation with CNO is found to be the most important determining factor in the Horizontal Branch stellar distribution, and therefore is the most appropriate ‘first parameter’ for HB morphology. The evolution of the stars is then considered, and the analysis of the interior structures provides a reclassification of HB track morphology into three categories, depending on whether the model contains an outer convection zone or a radiative outer envelope, and on the luminosity of the hydrogen-burning shell. Lastly, the question of the formation of red-giant stars is considered; the general conclusions of this part of the study support the arguments presented by Yahil and van den Horn (1985). Next, the evolution of the convective core of HB stars is reviewed, together with a detailed account of the numerical techniques developed for modelling semi-convection. The problems associated with the late phase of HB evolution are also discussed. A brief review of the physical inputs and numerical methods used in the interior is presented, focussing on the calculation and implementation of the Equation of State. The calculations performed for this study are then presented in detail. The effects of oxygen enhancement on zero-age sequences are illustrated for a range in metallicity, and theoretical relations between luminosity and metallicity for the ZAHBs are demonstrated. The evolutionary tracks computed are illustrated and summarized in extensive tabulations in the Appendices. The final chapter reproduces previously published studies of globular clusters. The first of these investigates the globular cluster NGC104 (47 Tucanae). By fitting the theoretical models to recent CCD photometry of the cluster, it was found that its initial helium content must have been close to 24% by mass. In addition, the best fits show that models for [Fe/H] = -0.65 provide an excellent match to the horizontal branch, if (m - M )v ≈ 13.44, and thereby yield consistency over the entire color-magnitude diagram of the cluster. The second study presents an investigation of the horizontal branch of M15. Detailed matches of our theoretical sequences to the cluster observations indicate that high envelope helium abundances are incompatible with the observed morphology. It is found that there is a clear preference for values of 0.21 ≾ Y ≾ 0.25, independent of the value of [O/Fe]. The precision of the method is reduced by uncertainties in the observations and in the available synthetic temperature-bolometric-correction relations. The oxygen enhanced zero-age HB models are found to have a period-colour relationship which is almost identical to that of their scaled-solar counterparts, but they reduce significantly the predicted double-mode variable masses. Importantly, it is found that, for reasonable assumptions about the reddening to M15, there is no discrepancy between the predicted and observed periods for the RR Lyrae variables. However, the period shift between M3 and M15 can be explained by canonical models only if the helium abundance in both clusters is low (Yhb ~ 0.21), and the bulk of the RR Lyrae star population in M15 is at late stages of evolution. These conclusions are reconsidered in the light of the new calculations presented here. / Graduate