Circumbinary planets are bodies that orbit both components in a binary star system. This thesis focuses on transits of these planets, which with the aid of the Kepler space telescope have recently led to the discovery of several such objects. First, transit timing variations - departures from strict periodicity in the transit times - are studied. These arise from both the motion of the host stars and relatively rapid precession of the planet’s orbit. Limits on the maximum possible transit timing variation are derived, and tested against N-body simulations of simulated circumbinary systems. These limits are then utilised to form a search algorithm designed to find these planets in light curves, focusing on data from the WASP and Kepler observatories. This search algorithm uses an individual transit search to identify potential transit signatures, then forms periodograms allowing for the possible timing variations. It is used to identify several new candidate planets, as well as confirm detections of previously known circumbinary systems. In addition a number of interesting multiple stellar systems are identified including the as yet unexplained KIC2856960, which display multiple eclipses, significant tidal heating or rapid orbital evolution on the timescale of the 4 year Kepler observations. In 2013 unbiased stellar radii for the eclipsing binaries of the Kepler dataset were not available. A catalogue is produced, derived from spectral energy distribution fits to data from the KIS, HES and 2MASS surveys of the Kepler field, which gives temperatures for these stars accurate to ~300K. These are then used to find calibrated stellar masses and radii. These parameters, in combination with the search algorithm, are used to study circumbinary planet rates of occurrence in the Kepler dataset. The known sample of eclipsing binaries is tested for detectability, and a Monte Carlo population synthesis used to find probability density functions for these rates. These are a function of the as yet unknown circumbinary planetary inclination distribution, and show that the rate of occurrence of circumbinary planets is consistent with that of single stars if these planets are in the majority coplanar with their host binaries. However, if they are more misaligned, to a degree greater than that implied by a 5° Gaussian distribution, their rate of occurrence becomes significantly higher. Furthermore, it is confirmed that planets of Jupiter size and greater occur less often in circumbinary configurations, and that circumbinary planets are preferentially found around binaries with periods longer than ~7 days.

The Earth receives all of its external energy input from the Sun (except for galactic sources), which consists of both particles of various energies and electromagnetic radiation of various wavelengths. The particles emitted from the Sun constitute the solar wind, from which the interplanetary magnetic field originates. These particles transport magnetic, thermal, and kinetic energy from the Sun to the Earth. The solar wind has two modes: slow (typical speed 400 km.r 1 ), and fast (typical speed 800 km.r'). Particles of various energies are released and accelerated into the heliosphere during (i) sporadic events involving both flares and coronal mass ejections, and (ii) recurrent events driven by co-rotating interaction regions associated with fast solar wind streams from trans-equatorial coronal holes. A small proportion of these particles, of which protons are by far the most significant for our purposes, deposit their magnetic and kinetic energy within geospace (defined herein as 'that which is within the magnetopause'). A survey of the solar energetic particle (SEP) events and trans-equatorial coronal holes occurring during solar cycles 19 to 23 confirmed that the cumulative frequency of SEP occurrence and the cumulative monthly averages of sunspot number exhibit a strong correlation which improves with the inclusion of successive solar cycles. Furthermore, there is good evidence that the emergence of low-latitude, open, coronal magnetic flux is also synchronised with the solar cycle. Four SEPs and one trans-equatorial coronal hole were then selected from cycle 23 for a detailed investigation of their effects on geospace. Specifically, the effects on the magnetosphere and the ionosphere are studied in relation to geomagnetic storms, cutoff latitude depression, substorms and polar cap absorption. The energetic proton populations of three selected SEP events from 2001 are used as 'tracers' to quantify the compression of the geomagnetic cavity during storm conditions. Empirical relations between the cutoff latitude and the ring current indices D,t and SYM-H are defined, and the compliance of the observations with the Tsyganenko TO] geomagnetic field model is tested during storm conditions ranging from quiet to severe. The TOl model was found to be limited in its utility during severe storm conditions (D8 < — lOOnT). Another selected SEP event from 2003, the 'Halloween flare', resulted in a polar cap absorption event for which empirical altitude-dependent relations have been derived between proton flux and D-region electron density. Values of effective recombination coefficient have been determined for both day and night. It was found that, though chemical models predict that the production and recombination process should deviate from a square law, there is actually no evidence for this in the observations. The D- and E-region effects of a co-rotating interaction region associated with the meridional crossing of a trans-equatorial coronal hole during late June 2005 have been investigated during periods of substorm activity in relation to electron density, cosmic-radio-noise absorption, and energetic electron fluxes. The hardening of the spectrum between the evening and morning periods is noted, and the movements of plasma during those periods are studied in detail, the motion being consistent with observations from previous related studies. The height and thickness of the absorption layer are estimated and the calculated total radio absorption is compared with measurement. The same co-rotating interaction region provided the opportunity to investigate the spatial and temporal variations of the trapped and precipitated electrons in the auroral regions in terms of flux, spectra, and pitch angle. Differences of spectral hardness between the trapped and precipitated electrons, with the time of day, and with the intensity, are noted. It is observed that, for the population on the day-side, the precipitated/trapped flux ratio is highly variable and is energy dependent in a manner consistent with the theory of pitch angle scattering. Another population, observed mainly on the night-side, shows near-isotropy at all energies observed. Diagrams of precipitated against trapped flux ('pitch-o-grams') are found to be helpful in identifying various electron populations. A method of determining the solar wind velocity from the delay in the B. is presented. The development of the event within the magnetosphere is described in detail, with particular reference to the results of the LISCAT observations. Comparisons are then drawn between a selection of fast solar wind streams and CMEs in relation to the Li environment, the magnetospheric cutoff latitudes and the energy deposited within the magnetosphere. Finally, the relative contributions of SEPs and fast solar wind streams to geomagnetic storms, cutoff latitude depression, substorms and polar cap absorption are compared.

This thesis presents a study of multiple phenomena that exist within the solar corona. The structures explored in this work cover a range of sizes from a small-scale X-ray bright point (<10 Mm), to medium-scale coronal loops(10–100 Mm), and finally to a large-scale prominence (>100 Mm). Observational data and numerical simulations were utilised in order to investigate the structure and evolution of each type of feature. A small-scale X-ray bright point (XBP) was investigated using complete Hinode observations in order to examine it over its entire lifetime (∼12 hours). The XBP was found to be formed directly above an area of cancelling magnetic flux on the photosphere. A good correlation between the rate of X-ray emission and decrease in total magnetic flux was found. The magnetic fragments of the XBP were found to vary on very short timescales (minutes), however the global quasi-bipolar structure remained throughout the lifetime of the XBP. Electron density measurements were obtained using a line ratio of Fe XII and the average density was found to be 5±1x109 cm−3 with the volumetric plasma filling factor calculated to have an average value of 0.04±15%. Emission measure loci plots were then used to infer a steady temperature of log Te [K] ∼ 6.1±0.1. The calculated Fe XII Doppler shifts show velocity changes in and around the bright point of ±15 kms−1 which are observed to change on a timescale of less than 30 minutes. The results indicate that higher cadence spectroscopic measurements are required if the velocity flows are to be related to corresponding changes in the magnetic field. The next feature investigated was a 100 Mm multistranded coronal loop that was simulated in order to investigate how changing the various model parameters would affect the resulting differential emission measure DEM distributions and intensity values. Once the model was fully understood, it was used to test a DEM solver and quantify the ‘goodness-of-fit’ that could be achieved. This allowed the imitations of the DEM method to be understood. As the model parameter space was altered, a number of changes in the resulting synthetic DEMs were observed. In most cases these changes were subtle and could be explained by the changing physics of the system. The cooling simulation showed the most unique changes where the total energy of the system could be identified by examining the evolution of the intensity values and DEM shape. The iterative solver solution XRT DEM iterative2 did an excellent job of reconstructing the original model intensity values and DEM distributions in the majority of cases. The only instance where the solver did not do well was when the synthetic DEM was very narrow i.e., only covering a few temperature bins. This highlights the under-constrained problem of using DEM solvers and shows that this particular solver works best when the original DEM being reconstructed is smoother and more multithermal. Finally, a large-scale prominence eruption was investigated using observations from two points of view. The structure and evolution of the prominence material and cavity were examined over the eruption process. Many possible initiation methods were investigated to see if the cause of the prominence eruption could be pinned down. It was found that the polar-crown cavity could be defined as a density depletion sitting above denser polar-crown filament plasma which has drained down from the cavity due to gravity. The eruption of the polar crown cavity as a solid body can be decomposed into two phases: a slow rise at a speed of 2 ±0.2 km s−1 , and an acceleration phase at a mean speed of 15–25 ±0.6 km s−1 . The initiation of the prominence was concluded to be caused by a combination of mass un-loading and a type of kink instability.

This thesis uses 32.88 1/fb of pp collision data gathered at the LHC by the ATLAS detector during 2016 at center of mass energy 13 TeV. The analysis employs kinematic fitting techniques by applying the KLFitter package on the signal-rich region using only the 6 jets selection mode (kB6). It construction variables providing good separation between signal and background in the search for ttH(H decay to b-barb) in the single-lepton final state (electron or muon). The scalar sum of transverse momenta is the variable of choice for the fit in signal-depleted regions. Using Boosted Decision Trees in the fit of signal-rich regions, a 95% CLs exclusion limit (significance) of 5.4 (4.25 \sigma) is obtained, with the corresponding ratio of the measured ttH signal cross-section to the Standard Model expectation of 3.69(+0.98,-0.88). This result indicates that there is an excess of events above the background expectation for the SM Higgs boson with mass of 125 GeV. The excess is even greater than the SM would predict (signal strength equal to 1). This excess over the SM prediction could be interpreted as a statistical fluctuation, and is not significant. More data would likely moderate this statistical aberration.

Much of the evolution of galaxies takes place in groups where feedback has the greatest impact on galaxy formation. By using an optically selected, statistically complete sample of 53 nearby groups (CLoGS), observed at radio (GMRT) and X-ray (Chandra and XMM-Newton) frequencies, we aim to characterise the radio-AGN population in groups and examine their impact on the intra-group gas and member galaxies. In this dissertation, low-frequency GMRT radio images of the nearby (<80 Mpc) central brightest group ellipticals from the high richness CLoGS sub-sample are presented for the first time at 235 and 610 MHz. Using the sensitivity to older electron populations at 235 MHz and the resolution of 610 MHz as a key to identify past and current AGN activity, a detailed analysis of the radio properties for each of the central group radio sources is performed, with the results being in addition combined with findings from the X-ray observations.

Desmoplakin is a cytolinker protein vital to tissue exposed to shear forces, such as the skin and the heart. This thesis research combines three physical techniques for the study of desmoplakin, namely Nuclear Magnetic Resonance (NMR) Spectroscopy, Small Angle X-Ray Scattering (SAXS) and Atomic Force Microscopy (AFM). The structure of the desmoplakin linker domain (in the C terminal end) has been resolved by NMR spectroscopy, exhibiting an unprecedented fold that contains a pair of regular and irregular subdomains and whose monomeric state has been confirmed by SAXS. The desmoplakin plakin domain (in the N terminal end) immobilisation on a surface of graphite decorated with size-selected gold clusters (with 55 and 147 atoms) was studied by tapping mode AFM, which provided evidence of enhanced weak adsorption of the protein to the clusters. With the aim of improving the technique of immobilisation of single biological molecules with metal nanoparticles, a new technique of cluster immobilisation has been developed using small metal clusters (Au\(_2\)\(_0\)) to create channels in a graphite substrate. These channels function as defects on the surface of the graphite to anchor soft-landed clusters with the potential to bind the biomolecules.

Accurate mass estimates for galaxy groups and clusters are important for understanding the evolution of matter within the universe. In this thesis we first discuss methods of mass estimation currently used within the literature, and introduce a set of scaling relations for mass estimation in cases where literature methods are not applicable. We find that methods based on group richness provide the best (i.e. lowest scatter) mass estimator. Secondly, we study the impact of feedback on hot group gas for a sample of optically selected groups. We refine the group selection using their dynamical state, identified through substructure in the distribution of member galaxies. We find this sample to be underluminous compared to an X-ray selected sample. Furthermore, with two groups showing high 2σ lower limits on entropy, the population of high entropy groups predicted by hydrodynamical simulations may have been detected. Finally, we combine measures of dynamical state and mass estimation scaling relations to understand how the presence of substructure can impact upon the ability to reliably estimate group and cluster masses. We find that substructure introduced through poor group identification has the largest effect on the quality of the final mass estimates.

The latest generation of space missions have performed large scale observations of stars and this has been revolutionary in the field of asteroseismology. The ability to characterise thousands of stars has been instrumental in understanding the interiors of stars and the evolution of the Galaxy. This thesis focuses on studying red giant stars, both on an individual basis and as a population, using a robust asteroseismic metric we define based on the bandpass filtered estimate of the stellar variance. Here we present results of testing asteroseismic scaling relations, and the assumptions needed to create realistic simulated power spectra. The resulting synthetic datasets then inform three other investigations. We present the results of an investigation into determining the binary population of Kepler red giant branch stars using our variance metric. The inferred fraction of 57.4 +/- 2.5% is consistent with previous work on main sequence stars. Results of using our variance metric as part of an analysis pipeline, designed to automate the detection of solar-like oscillations and determine global asteroseismic parameters in K2 and CoRoT data are presented. Finally, we present a discussion of using ourvariance metric to highlight structural differences between red giant branch and red clump stars.

Superclusters appear as large-scale structures in the form of a network of filaments, and can be up to 100h\(^{-1}_{100}\) Mpc in extent. In this dissertation, we investigate in detail the spatial structure of the three richest superclusters of galaxies closer to us then z=0.1. We investigate the rate of star formation in galaxies at various positions among the filaments and clusters in the Pisces-Cetus Supercluster. We use an index of star formation derived from a principal component analysis of optical spectral. We have shown that galaxies which are members of these filaments, show a steady decline in star formation rate, from the periphery of a cluster, into the cluster core. However, on top of this trend, we find a nearby instantaneous enhancement of the rate of star formation at ~3h\(^{-1}_{70}\) Mpc from its centre. We conclude that the most likely reason for this sudden enhancement in star formation rate is galaxy-galaxy harassment. Further work shows that the enhancement in star formation occurs mainly in the in falling dwarf galaxies (-20 < MB < -17.5) and that there is little evidence that the tidal effect of the dark matter haloes of the clusters is responsible for the enhanced star formation. The results of an analysis performed on a larger ensemble of 52 filaments were consistent with those from our smaller sample drawn from the Pisces-Cetus supercluster. We conclude this study with the analysis of a sample of spectra from the 6dF redshift survey. In the absence of spectrophotometric calibration, for these galaxies we were only able to obtain an uncalibrated star formation rate, but we could examine the effect of correction due to dust extinction, and could separate the starforming galaxies from the active galactic nuclei. From our small sample, there was interesting evidence of enhanced star formation in galaxies at similar distances from the centres of the clusters in the Shapley Supercluster.

Gravitational-waves provide a unique probe of the stellar remnants---black holes and neutron stars---left behind at the end of massive stars lives. On the 14th September 2015 the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO) made the first direct detection of gravitational waves from a merging stellar mass binary black hole, GW150914, during its first observation run (O1). In this thesis we present Compact Object Mergers: Population Astrophysics and Statistics (COMPAS). COMPAS is a platform incorporating astrophysical modelling tools and statistical analysis tools to extract information from the population of merging binary black holes we observe. We demonstrate that the masses, spins and observed rate of binary black holes can offer new insights into their formation.