No description available.

A multiwavelength analysis of M31’s globular clusters and their low mass X-ray binaries by Mark B. Peacock Globular clusters (GCs) are dense groups of thousands to millions of stars. They are often very old systems with ages similar to those of their host galaxies and the early Universe. These clusters provide unique laboratories for astrophysical research and have been used by countless studies to improve our understanding of the Universe. In particular, they are ideal locations for studying stellar evolution and the formation and evolution of galaxies. They also provide unique locations for studying individual exotic objects, such as X-ray binaries. In this study, I investigate the properties of GCs in the nearby spiral galaxy, M31. This galaxy hosts the largest GC population in the Local Group. This, combined with its relative proximity to us, makes it an important bridge between studies of Galactic and extragalactic GCs. However, previous catalogues of these clusters have suffered from significant inhomogeneity and contamination from both stars and galaxies. In this contribution I present new, homogeneous, optical and near infra-red photometry of the M31 GC system. In addition to this, the structural parameters for over half of the known clusters are determined through fitting point spread function convolved King models to their density profiles. This photometry is used to remove significant contamination from non-cluster sources in previous cluster catalogues and to confirm a large population of young clusters in the M31 cluster system. Determining the properties of these clusters is very important in investigating both this, and other, GC systems. It is also of great benefit in investigating the exotic objects hosted by these clusters. I combine these data with archived XMM Newton observations, to study the low mass X-ray binaries (LMXBs) in M31’s clusters. LMXBs are known to be relatively common in GCs and, through studying the properties of the GCs which host them, it is possible to investigate the effects of cluster environment on the formation and evolution of these systems. From this work, I demonstrate that the presence of LMXBs is proportional to the stellar collision rate of a GC. This provides good observational evidence that these LMXBs are formed through dynamical interactions. These data are also used to consider the morphology of horizontal branch stars in M31’s GCs. Published GALEX ultraviolet observations of these clusters are used as a probe into their hot stellar populations. From this work, I propose a relationship between the core density of these clusters and their ultraviolet colour. This result suggests that the formation of (FUV bright) extreme horizontal branch stars may be enhanced in dense stellar environments through stellar interactions

When we consider in detail the behaviour of a fluid consisting of two (or possibly more) interpenetrating components, the likelihood of dynamical instabilities induced by coupling between the two fluids cannot be ignored. The phenomenon is generic to all such multi fluid systems and as such is appellated the two-stream instability. Mathematically this class of instability is somewhat akin to the more well known Kelvin Helmholtz instability, but is distinguished by the fluids flowing through each other rather than having a clearly defined interface between them. In this thesis we describe in some detail the mechanisms underlying this instability in a simple linear ow scrutinising in particular the growing (unstable) solutions for small harmonic perturbations. We further consider the application of this genre of instabilities to other physical systems, most conspicuously to that of a rotating super fluid body with rotational lag between the components. This case is of particular interest in neutron star physics, where it offers possibilities for exploring behaviour within the core. There also seems to be the chance of exploring this example in laboratory systems. We also take a tentative first step to extending the application and understanding of the two-stream instability by flirting with the analogous observations in a laboratory realisable binary Bose-Einstein Condensate. This laboratory realisation is a first step towards being able to explore physically issues relating to neutron star dynamics. We further discuss general analogue systems for modelling key features of neutron stars in terrestrial laboratories. The possible applications, along with some of the diffculties in using these analogues, are explored.

No description available.

A low energy gamma ray telescope, and the results of its observations are described. The telescope consisted of four sodium iodide crystals, each of 120 cm(2) area, occulted by lead discs. Charged particles are rejected using scintillation, anti-coincidence shields. The telescope was flown from Palestine, Texas in 1974. Gamma rays were observed from the Grab Nebula, the pulsar NP0 532, and the atmospheric background. No evidence for a gamma ray burst was found, giving an upper limit of less than 5.8 x 10(3) bursts per year of intensity greater than 1.6 x 10(-6) ergs cm(-2) Various types of existing, and planned, gamma ray detectors, and successful gamma ray observations are reviewed. Detailed calculations of the detection efficiency of a Double Compton telescope are presented and these results led to the development of the MISO low energy gamma ray telescope. Preliminary calculations of the detection efficiency of an Anticollimated Double Compton telescope are presented, which suggest that further, more detailed investigation of this type of detector would prove fruitful.

This thesis presents analyses of flickering aurora observed using the state-of-theart Auroral Structure and Kinetics (ASK) multi-monochromatic ground-based auroral imager. Flickering aurora is observed as rapid (typically 2–20 Hz) oscillations in auroral luminosity. There are several competing theories for the generation mechanism of flickering aurora, although all use electromagnetic ion cyclotron (EMIC) waves. The work presented in this thesis has shown that precipitating electrons producing flickering aurora are accelerated by Landau damping of the EMIC wave, and that the wave parallel phase velocity is the primary factor limiting the electron precipitation energy. In addition, evidence is presented supporting the theory that very small structures in flickering aurora are caused by interference between multiple EMIC waves. A combined electron transport and ion chemistry model (the Southampton Ionospheric Model) has been used in this work to allow quantitative estimates of the energy of precipitating electrons responsible for aurora observed with ASK. This thesis also presents a novel technique for intercalibrating optical and particle measurements of the aurora made by instruments onboard the Reimei satellite using the Southampton Ionospheric Model. This allows estimates of the flux of precipitating electrons at high energies above the detection limit of the Electron Spectrum Analyzer (ESA) particle detector. Optical images of the aurora obtained using the Multispectral Auroral Camera (MAC) instrument are also calibrated, allowing quantitative estimates of the auroral brightness without contamination from background light and auroral light reflected from the Earth. The technique has many possible applications in auroral studies using the Reimei satellite.

The known population of high-mass X-ray binaries in the Small Magellanic Cloud is continually growing and is now a similar size to that of the Milky Way, despite a significant mass difference between the two galaxies. In this thesis, I present multi-wavelength observations of Be/X-ray binaries that have undergone an outburst during the past three years, including the discovery of new systems and extended outbursts from previously known sources. The results are discussed in terms of both the underlying physics of individual outbursts and how the growing SMC population is helping our understanding of the formation and evolution of highmass X-ray binaries. In particular, I describe the orbital analysis of every extended X-ray outburst detected by the Rossi X-ray Timing Explorer and present the first significant sample of systems outside of the Milky Way for which a binary orbital solution is known.

The relationship between the X-ray and optical variability in Seyfert galaxies by Elm´e Breedt Lategan Seyfert galaxies have been known to vary since shortly after their discovery, but the origin of the optical variability and its relationship to the X-rays, have not been well established. Presented here is a comprehensive comparison between the long term X-ray and optical emission in a sample of seven Seyfert galaxies, to determine the relationship between the X-ray and optical variations. It is shown that the observed optical variability is the sum of several independent mechanisms: the short time-scale variability is dominated by X-ray reprocessing, but variations intrinsic to the disc, such as propagating accretion rate fluctuations, add considerable variability power on long time-scales. Cross-correlation analysis reveal a statistically significant correlation between the X-ray and optical emission of all the galaxies under investigation, with the optical variations following the X-rays by 1–2 days. This time-scale is consistent with the expected light travel time from the central X-ray source to the optically emitting region of the accretion disc. Although this is a strong indicator of X-ray reprocessing by the disc, it is also clear that reprocessing cannot account for all the optical variations observed. At least one source displays clear long time-scale (years) variations in the optical with no apparent counterpart in the X-rays, and in others the long term optical amplitude exceed that of the X-rays. It is shown that these long time-scale optical variations must originate from an independent variability mechanism, possibly variations in the accretion rate or the geometry of the system. There is also evidence that there may be a significant contribution to the optical emission from as far out as the dust torus. Finally it is shown that there may be a dependence of the strength of the X-ray/optical correlation on the disc temperature and black hole mass.

The galaxy stellar mass function (GSMF) has been well measured by the Galaxy And Mass Assembly (GAMA) survey down to a mass of $\mstar = 10^{8}\,\msun$. Below this mass the values produced so far can only be taken as lower limits on the distribution. One source of this incompleteness is failing to account for undetected low-surface-brightness galaxies (LSBGs) within the fields observed. These galaxies have been known about for some time, however, taking a true census of their population is difficult because of the biases associated with their detection in large surveys. The focus of this thesis is to improve the census of these objects and to try and apply those results to the low-mass end of the GSMF. First the SDSS data used to create the original GAMA catalogues is re-examined for low-surface brightness galaxies (LSBGs). To accomplish this SDSS DR7 imaging was used and a specialised detection algorithm created. This was based on masking sources detected with SDSS \textsc{photo}, combining the {\it gri} images with a weighting that maximises the signal-to-noise (SNR), and smoothing the images. These were then run through a detection algorithm which finds all pixels above a set threshold and groups them based on their proximity to one another. The list of detections is cleaned of contaminants such as diffraction spikes and the faint wings of masked objects. This produces a final list of 343 newly discovered LSBGs. Measuring their $g-i$ and $J-K$ colours shows that most are likely to be at redshifts less than 0.15. The photometry is carried out using a flexible auto aperture for each detection giving surface brightness measurements of $\mu_{r} > 23.7$\,mag arcsec$^{-2}$ and $r$-band magnitudes of $r_{AUTO} \gtrsim 20$\, mag. Through this method we show there are at least 343 new LSBGs within the GAMA fields, however none of these galaxies are bright enough to be within the GAMA main survey limit. It was noticed during the previous work that the detected LSBGs were all visible in VIKING $Z$-band data, and so it was decided to run a more traditional detection algorithm over these data to increase the number of LSBGs detected. This could then be used to create a new GSMF based on the deeper $Z$-band imaging. By using this imaging it will be possible to detect many more faint galaxies than previously and also increase the depth to which surface brightness can be effectively probed. The three GAMA equatorial regions have had mosaics created from the $Z$-band imaging which are searched using \textsc{Source Extractor} (\textsc{SExtractor}) and catalogues of detections are made. These are then compared to the original GAMA catalogues to remove duplicate detections and identify any possible new ones. Criteria are then applied to the source lists to remove any stars or objects which are either not galaxies or artefacts. This then leaves only likely galaxies in the catalogue to be used. The next stage is to create the GSMF based on the data collected, through applying corrections for the volume searched, and the spectroscopic completeness of the objects after they have been binned in $g-i$, $J-K$, and apparent magnitude. The GSMF created is compared to previous versions, namely that from \cite{Baldry+2012}, and a rise in the number density at masses of $\mstar \le 10^{8}\,\msun$ is shown. These can still only be thought of as lower limits however as improvement to the imaging can still be made in future surveys. With a full catalogue obtained using the VIKING Z-band it was decided to revisit the detection algorithm developed in Chapter 2. A pilot study was undertaken to both test the validity of the method, and the suitability of the VIKING images for further study. Whilst applying the detection algorithm to the data improved the ability to detect low surface brightness features within the images, no new galaxies were discovered over the pilot study area of $0.75$ deg$^{2}$. This method applied to the Z-band data, even over the full area, is unlikely to lead to large numbers of new LSBGs. This work has shown that there are still LSBGs in the field to be discovered. The result of finding new LSBGs has been to raise the measurement of the GSMF at low masses, further constraining the number of low mass galaxies in the Universe.

Collisions is one of the most important processes in the Solar System that have played a significant role in its evolution for 4.5 Gy. They are responsible for the formation of asteroid families, craters and regolith production on bodies surfaces. Moreover they pose a hazard for our planet's environment, human civilisation and space assets. Impacts have shaped the asteroids and their surfaces and recently there are indications that they are also responsible for the creation of multi-lithology asteroids. The effectiveness of this process lies, apart from the collisional speed and angle, on the physical parameters of both the target and the impactor. A plethora of laboratory experiments are devoted to study the outcome of impacts, from low speeds of a few m/s to greater speeds of several km/s. In addition space missions; such as Deep Impact (NASA) in the past and AIDA (ESA/NASA) hopefully in the near future, are aiming to perform hyper-velocity impact experiments at large scales. Although there is advance in our understanding of crater formation, target fragmentation and ejecta speeds, however the fate of the impactor is still very poorly constrained. Experiments so far were focused using materials not directly relevant to the composition of asteroids. We start an investigation for the impactors' fate, by using lithological projectiles that impacted three different types of targets with different material and bulk porosities. For this experimental campaign was used the Light Gas Gun (LGG) of the Impact Group at the University of Kent. The study was focused on three main topics: i) the fragmentation of the impactor, ii) the implantation of exogenous material onto the target and iii) the inspection of the final state of the projectile.\\ This Thesis is divided in six Chapters. The first two, Chapters 1 and 2, are giving a review of recent advances of small bodies studies, the importance of collisions in the Solar System, and a brief description of the laboratory impact experiments, providing the current state of research on the fate of projectiles. Some open questions lead to the explanation of the aim of this study. In Chapter 3 are described the series of experiments performed, explaining the analysis methods were developed and the way that the main topics of fragmentation, implantation and characterisation of the impactor were studied. All the results for each one of these topics, along with the difficulties during the experimental procedure are provided in Chapter 4. In Chapter 5 we discuss the results giving the implications, attempting to place the outcome in the big picture of the small bodies collisions. In the last Chapter 6 there is a summary of this work, providing also possible future ideas for the continuation of this study.