The field of exoplanetology has evolved significantly from its beginnings in the 1990s, gradually shifting emphasis from the detection of new exoplanets to characterisation of those already discovered. Simultaneously, considerable progress has been made in the area of automatisation of both instruments and data reduction techniques, leading to an ever-growing influx of new data, discoveries and facts about the planets outside of the Solar System. Observations of transiting exoplanets can be divided into two major themes: surveys, designed to find new planetary candidates; and follow-up observations, which offer a chance to learn more about the characteristics of the previously identified candidates and confirm their planetary nature. In this thesis, I introduce both aspects in the context of the current exoplanetary re- search, and go on to describe in considerable detail the objects of two observational follow-up projects, planets WASP-12 band KIC 12557548 b, together with a selection of new techniques I develop to assist in data reduction and analysis of large photometric datasets. In the WASP-12 b study, I use ULTRACAM on the William Rerschel Telescope to search in the visible light for the presence of the early ingress signature, observed previously with the Rubble Space Telescope in the near-ultraviolet. I also investigate claims of a transit timing variation in this system. I use the same instruments to carry out KIC 12557548 b observations, with the aim to measure the colour dependence of the extinction and scattering due to the dust in the tail of the putative planet and provide direct evidence in favour of this object being a disrupting low-mass rocky planet, feeding a transiting dust cloud. I also present a new algorithm used to correct for scattered light in astronomical images, ULTRACorrect, and introduce a bespoke photometry pipeline, ULTRAPhoto, together with a selection of other methods useful in observations planning and data analysis

Venus Express is the first European mission to Venus and will help to answer questions such as: What governs the escape processes of the atmosphere? How did it end up with the atmospheric state it's currently in? What role does the green-house effect play on Venus? These are important questions for the evolution of Earth. The solar minimum in 2009 was one of the lowest on record, and by 2006 minimum conditions were already in place. Utilising the Analyser of Space Plasma and Energetic Ions (ASPERA-4) Ion Mass Analyser (IMA) and the paired magnetometers on board Venus Express the relation between the ions and flux ropes are examined. First, by using the magnetometer to identify the flux rope in the ionosphere and then by using the IMA to point out interesting coincidences. The altitude of ropes are dependent on the time spent in the ionosphere; the ropes which had been in the ionosphere longer had an increased weight. However, the occurrence of flux ropes and a high and low energy populations of ions is coincidental. Venus has no substantial magnetic field and thus it currently it has no barrier to solar wind scavenging of the atmosphere, despite which the atmosphere on Venus is dense. Flux ropes are investigated to determine whether they a part of the replenishment or loss of atmosphere. Venus boundaries are examined during 2007, and 2011/2012 going toward solar maximum. A new use of the transition parameter is put forward; to aid with boundary placement. The bow shock is located with an automatic algorithm and this is then compared with previous models, giving a sense of Venus reaction to solar activity. It is shown that the bow shock position is largely unchanged. The ion composition boundary and the magnetic pile-up boundary are also located. They coincide to within one IMA accumulation period, but the Ion Composition Boundary (ICB) is in general inside the Magnetic Pile-up Boundary (MPB). Finally, solar transients at both solar minimum and solar maximum are investigated to see whether they increase the loss rate. During solar minimum the passage of comet 2P/Encke, and of two Coronal Mass Ejections (CME) and a co-rotating interaction region were investigated. In solar maximum three potential CMEs are selected using the WSA-Enlil solar wind prediction model and then the real data are compared to Enlil predictions. It is found that when the comet 2P/Encke was in the vicinity the concentration of high energy ions, especially oxygen, was raised. CMEs interacts with the Venus magnetosphere to add heavier ions to the solar wind.

An experiment to study cosmic ray extensive air showers of size exceeding 3.107 particles has been constructed on the Yorkshire Moors at Haverah Park, near Harrogate. The preliminary operation and results from this experiment are described. The extensive air showers are recorded by a triangular array of water Cerenkov detectors spaced at distances of 500m from a control detector. During the setting up of the main array, the prototype Cerenkov detector units were employed in two subsidiary experiments. The first of these, described in Chapters 2 and 3, consisted of a small array of single basic detector units (single water-tanks). This array was the same shape as the large array but had an array spacing of 6m, and was used to study the distribution of energy in the electron-photon component of extensive air showers at distances within 12m of the shower axis. The second experiment, which is described in Chapter 4, employed different combinations of the basic detector unit to investigate the density spectrum at very low densities. The results yielded information on the character of very small air showers, and indicated the manner in which the transition in density spectrum contributions from single particles to extensive air showers takes place. Finally, the preliminary results of the main 500m array are presented and discussed, particularly with relation to determining the lateral distribution of the Cerenkov detector response and the problem of ascertaining the absolute shower size. A possible normalisation procedure applicable to all zenith angles is suggested. The initial results on the shower absorption, size spectrum and shower front curvature are given and compared with those of other workers. A number of suggestions for future work have been listed and the feasibility of an array to study even larger showers has been investigated.

The subsurface temperature distribution of airless bodies across the Solar System can provide important clues to their formation and evolution. This thesis investigates the lunar soil temperature profile using data from the recent Chinese lunar orbiting spacecrafts Chang'E 1 and 2 to explore variations in the subsurface temperature of the Moon. These variations include heat flow information of the subsurface and the interior of the Moon. Before the launch of Chang'E-1 (CE-1), the temperatures of the deep layers of the Moon have only been measured at the landing sites of Apollo 15 and 17 by in situ temperature probes. The CE-1/2 lunar orbiters were both equipped with a 4-frequency microwave radiometer (MRM) to detect the lunar surface brightness temperature (TB) and to retrieve data on lunar regolith thickness, temperature, dielectric constant, and other related properties. The MRM can penetrate to a nominal depth of 5 metres in the subsurface with the 3 GHz channel. This research aims to develop a radiative transfer forward model for an airless body and then utilize MRM data to study an observed anomaly of elevated 2 m deep TBs measurements in the Oceanus Procellarum region on the lunar subsurface. After initial validation of the MRM data and modelling of the lunar regolith parameters, a multi-layer radiative transfer forward model has been derived using the fluctuation dissipation theorem. The forward model calculates the radiometric contribution from several depths on the TB that would be observed by the MRM instrument around the Moon (at different frequencies), as a basis for an inverse method. Sensitivity analysis indicates that, as expected, mineralogy and density information are very important to the inverse calculation. Therefore new FeO/TiO2 distributions derived from the Moon Mineralogy Mapper (M3) were incorporated into the calculation. The derived FeO/TiO2 distributions were also used to derive the bulk density of the lunar surface which was also incorporated into the calculation. The forward model was then used to invert the MRM measured TB data to generate 2 m depth subsurface temperature profiles. The provisional results show that, as expected, the 2 m subsurface temperature is potentially correlated to the distribution of radioactive elements such as uranium and thorium in the lunar crust. The 2 m subsurface temperature map was then converted to a lunar heat flow map, which was validated by the Apollo 15 and 17 measurements. Inspecting this heat flow map, abnormal high heat flow in the Oceanus Procellarum KREEP Terrain (PKT) region was noticed. The PKT is enriched with a high abundance of radioactive elements such as uranium and thorium. Hence a heat flow model based on radioactive elements as well as internal cooling was built up to investigate such a finding. In this thesis, a radiative transfer model for the analysis of MRM was developed and proven to be a useful tool for studying the lunar heat flow, as well as subsurface temperature. Rough surface scattering effects on the MRM measured TB values were also analyzed for future calibration. Possible improvements to the MRM instrument design are discussed in the future work as well as the possible application of the MRM instrument on the Martian surface.

,. Subdwarf B (sdB) stars are thought to be core helium-burning stars which populate on the extreme blue end of horizontal branch in a Teff-logg diagram. Their atmospheres are generally helium deficient. However, almost 10% of the total subdwarf population comprise stars with helium-rich atmospheres. Helium-rich subdwarf B (He-sdB) stars represent a small group of low-mass hot stars with luminosities greater than those of conventional sdB stars and effective temperatures lower than those of sdO stars. The optical spectra of He- sdB stars are characterised by strong HeI and weak Hell lines. The most numerous He-sdB stars are both very H-poor and N-rich. Some show C-enhancement, and a few are moderately H-rich. We have carried out a detailed abundance analyses of He-sdB stars using high-resolution optical spectra. Line-blanketed LTE model atmospheres have been used to derive atmospheric properties and elemental abundances. By measuring their surface chemistry, we have explored the connection between He-sdB stars, He-sdO stars and sdB stars. We demonstrate a clear distinction between extreme He-sdB stars and intermediate He-sdB stars. The extreme He-sdB stars are mostly N-rich, a few show neon enrichments and might be best explained by the merger of two helium white dwarfs. Intermediate He-sdB stars mostly exhibit strong unusual elemental abundances. They are located roughly between the extreme He-sdBs and sdBs in Teff-logg diagram and are thought to be transition object from a helium-rich to a helium-poor phase. This work reports the first discovery of strontium, germanium, yttrium and zirconium in the optical spectrum of a hot subdwarf, LSIV-14 116. This is an intermediate He-sdB star which shows 4dex overabundance of zirconium, strontium and yttrium and 3dex overabundance of germanium. This work also reports 0.63dex overabundance of argon in another intermediate He-sdB star CPD-20 1123. It is argued that these abundance anomalies can be explained by radiatively-driven diffusion.

Despite years of intense research on the exact nature of core-collapse supernovae (CCSNe). much uncertainty still surrounds the progenitor systems of these explosions. Only the most common subtype (SNIIP) has a known origin. thanks (0 numerous direct observations of the progenitor stars. This thesis aims to constrain the progenitors of all subtypes of CCSNe by looking at the environments in which they explode, and to use the statistical distributions of the different' core-collapse subtypes to probe the star formation properties of interacting galaxies. I will present an analysis of the distributions of a large sample of CCSNe (278) in isolated and interacting host galaxies. paying close attention to the selection effects involved in conducting host galaxy supernova studies. When taking into account all of the selection effects within the host galaxy sample, the following conclusions are drawn: Within interacting, or 'disturbed', systems there is a real. and statistically significant. increase in the fraction or stripped-envelope supernovae (SE-SNe) in the central regions. Selection effects are shown not to drive this result, and so it is proposed that this study provides direct evidence for a high-mass weighted initial mass function within the central regions of disturbed galaxies. o Within 'undisturbed' spiral galaxies the radial distribution of type Ib and type Ic supernovae is statistically very different, with the latter showing a more centrally concentrated distribution. This could be driven by metallcity gradients in these undisturbed galaxies, or radial variations in other properties (binarity or stellar rotation) driving envelope loss in progenitor stars. This result is not found in 'disturbed' systems. where the distributions of type Ib and Ie supernovae are consistent. o There is an absence of SNIIn in the central regions of host galaxies, specifically there is a lack of faint SNIIn within 50 per cent of the host galaxy light. Whilst assumptions may indicate that this is an extinction effect, there is also a lack of bright SNIIn events in the outer 50 per cent of host galaxy light. This radial correlation with absolute magnitude may indicate an inherent population dependence on host galaxy environment. o The distributions of SNIIn and SNIe are found to be statistically very unlikely (0.1 per cent) to be drawn from the same parent population within this supernova sample. Literature suggests that the progenitors of both of these populations are very massive stars ( 50 M0 ), if this is truly the case then the very different distributions of each subtype becomes difficult to reconcile.

Recent cosmological observations have suggested that the universe is under- going accelerated expansion. This can not be explained within the framework of General Relativity and the Standard Model of particle physics, which has been dubbed the dark energy problem. In this thesis, we study the possibility that dark energy originates from modifications of General Relativity on very large scales. The Gauss-Bonnet term arises naturally in string theory as a higher order correction to the Einstein-Hilbert term. Upon compactification to 4 dimensions, it can give rise to 1(9) gravity, 9 being the 4D Gauss-Bonnet term. We reduce a general 1(9) model in the FRW background to an autonomous system, via which we systematically classify general 1(9) models. As a result, easy-to-use criteria are employable to check whether a given 1(9) model can produce a viable background evolution. Galileon modified gravity, in which modifications to General Relativity are encoded in a scalar field called the galileon, is motivated by certain braneworld scenarios. One simple example is the Dvali-Gabadadze-Porrati model, where the brane bending mode plays the role of the galileon in the decoupling limit. Unlike the DGP model, ghost-free self-accelerating branches can exist in general galileon models. We study the multi-field generalisation of the galileon model. By an explicit example, we show that a higher eo-dimensional braneworld model can give rise to an effective 4D theory with multiple galileons. We find that certain multi-galileon models are phenomenologically healthier than the single galileon model, and admit self-tuning backgrounds where the gravitational effects of a (small) cosmological constant can be dynamically cancelled away, which is an explicit example of degravitation. We argue that the effective galileon field theory can have an internal symmetry if the underlying braneworld model has certain geometric symmetry in the bulk, and explicitly construct models with the SO(N) and SU(N) fundamental and ad- joint symmetries. Also, we find that in symmetric multi-galileon models a generic self-accelerating vacuum will spontaneously break the internal symmetry, whose pattern can be described by a variant of Goldstone's theorem. Observationally, this may be reflected in tests of gravity on very large scales.

No description available.

The formation and evolution of protoplanetary disks is simulated by computer modelling, using the Smoothed Particle Hydrodynamics (SPH) method. The suitability of SPH for modelling disks is investigated, and problems are identified with the SPH implementation of Artificial Viscosity in disks with Keplerian velocity profiles. Analytical and experimental results reveal that the resultant viscous force for a simulated Keplerian disk is in the opposite direction to that produced by linear shear. Applying Artificial Viscosity only to approaching particles results in a radial force four times larger than the force in the direction of the orbit. The viscous force can change direction if temperature, and therefore sound speed, decreases. Techniques for activating Artificial Viscosity only when convergence is detected are found to fail in differentially rotating disks. Both the Balsara Switch and Time Dependent Artificial Viscosity use the SPH estimate of V v sph, which has a low freqency time varying component which is independent of h, and so cannot be removed by increasing the number of SPH particles. An alternative method, based on pattern recognition, is shown to reduce the viscous spread of a differentially rotating ring by an order of magnitude. We also identify problems associated with the gravitational field of disks. The use of an annulus to represent a portion of a much larger, continuous disk, may yield unrepresentative results. The edge effects can cause preferential accretion zones, where the Toomre Q parameter is not the same as it would be for the same region of an extended disk. SPH simulations of Protoplanetary disks produce condensations which do not persist long enough to collapse. The high tidal shearing forces in a Keplerian accretion disk disrupt the condensations before they accumulate enough mass to collapse. Including a more realistic treatment of the thermal physics, and reducing the effective shear viscosity, makes the situation worse.

Binary star formation is the dominant mode of star formation, in contrast to the traditional picture of single star formation. The work in this thesis investigates the properties of binary stars with the aid of numerical simulations, using N-body and Smoothed Particle Hydrodynamics codes. First, we develop a simple model of isolated binary star formation assuming prestellar cores fragment due to rotational instabilities into a ring of J f (< 6) stars. We follow the decay of this small-N cluster into singles and multiple systems using the N-body code NBODY3. We can reproduce most of the observed stellar and binary properties of young stars, including the high multiplicity and wide separation distribution, in low-mass star forming regions like Taurus. We extend this further into a model of clustered binary star formation assuming 100 small-N clusters form in fractal clusters of radius 1 pc, similar to many young embedded clusters. We follow the dynamical interactions of these clusters using the N-body code NBODY6. We find that disruptive binary-binary encounters in dense clusters can explain the differences between binary properties in low-density and high-density star forming regions. We develop a new test of Smoothed Particle Hydrodynamics (SPH) called the Jeans Test. We demonstrate that SPH correctly models fragmentation and that under-resolved SPH simulations supress real fragmentation rather than promote artificial fragmentation. Thus binary and multiple systems produced in SPH simulations are real and not the result of numerical effects. Finally, we perform simulations of turbulent prestellar cores in the context of binary star formation. We extend the work of Goodwin, Whitworth & Ward-Thompson (2004) by investigating 2.17 M0 and 4.34 M0 cores.