Active galactic nuclei (AGN) are some of the most energetic objects which have ever been observed and each of these harbour a supermassive black hole at its centre. By looking at the X-ray emission from these nuclei, information can be gathered regarding their inner workings. Emission from regions which are very close to the central black hole can be subject to strong relativistic effects and the examination of this emission can lead to the placing of estimates upon the rate at which the black hole is spinning. Within this thesis, I make an analysis of all Seyfert 1 observations which have been observed with Suzaku to date, although using selection criteria such that broad features in the FeK region can be observed if they are indeed present. Models are constructed of the time-averaged broadband spectra over 0.6-60.0 keV, which accurately describe these complex AGN and allow the measurement of the impact relativistic effects have upon the X-ray spectrum. There are a total of 46 different objects and 84 observations used within this analysis. By conducting a full broadband analysis of these AGN, supermassive black hole spin constraints are placed upon 11 objects, 7 of which are unique to this analysis with the remaining 4 either confirming or improving upon previous analyses. In general, it is found that 50% of the objects in this sample show evidence for emission from the inner regions of the nucleus although none of the AGN require a maximally spinning black hole, which is in contrast to the results in alternative analyses. The data within this thesis are best described with emission originating from no further in than a few tens of Rg.

Convection plays a key role in the evolution of massive stars. Despite many decades of work on this topic, the treatment of convection (convective boundary mixing in particular) is still one of the major uncertainties in stellar evolution modelling. Fortunately computing power has reached a level that enables detailed three dimensional hydrodynamic simulations, these can provide valuable insights into the processes and phenomena that occur during stellar convection. The aim of this thesis is to explore the physics responsible for convective boundary mixing within the deep interiors of massive stars, through the calculation of stellar evolution and three-dimensional hydrodynamic models. The latter focus on carbon shell burning and are the first of their kind within the stellar hydrodynamic community. To prepare the input models as well as study the evolution of convective boundaries, a 15M⊙ stellar model was computed and a parameter study was undertaken on the convective regions of this model. The carbon shell was chosen as an input model for three-dimensional simulations. Two sets of simulations were calculated with the aim of conducting a resolution study and luminosity study. The simulations were analysed using the Reynolds averaged Navier-Stokes (RANS) framework and within the context of the entrainment law. The following is a summary of the key findings. The lower convective boundary was found to be ‘stiffer’ (according to the bulk Richardson number) than the upper boundary. The boundaries are shown to have a significant width which is likely formed through Kelvin-Helmholtz instabilities, the width of the lower boundary is much narrower than the upper. The shape of the boundaries (interpreted through the composition) is smooth and sigmoid-like, whereas in the one-dimensional models it is sharp and discontinuous. Finally, these simulations confirm the scaling of the bulk Richardson number with both the entrainment rate and the driving luminosity.

The WASP project has discovered many transiting gas giant exoplanets. Some of these exoplanet systems have been observed by the K2 space-based telescope. The much higher photometric precision, shorter cadence and extended continuous follow-up observations provided by the K2 mission enabled the most detailed photometric characterization yet of the WASP and other planetary systems presented in this thesis, which contributes to our understanding of how planets form and evolve. I analysed the majority of transiting exoplanet systems observed by the K2 in the 1-min short-cadence mode within the first 14 regular observing campaigns. I present here the analysis and results for a total of 10 planetary systems observed in the short-cadence mode. I detected starspot occultation events in two aligned and one misaligned planetary system and proved that detecting starspot occultation events is possible in the K2 data. I also detected optical phase-curve modulations in two systems, rotational modulations in four and γ Doradus pulsations in one planetary system. I refined the system parameters for all short-cadence targets and used non-detections to provide tight upper limits. In addition, I discovered a hot Jupiter using the long-cadence K2 data and refined the ephemeris with the WASP data of another K2-discovered planet.

The observed correlations between the masses of supermassive black holes (SMBH), MBH, with a gravitational influence on parsec scales, and properties of the host galaxy, measured on kiloparsec scales, strongly suggest that the SMBH and galaxy co-evolve. These correlations are likely to be a reflection of a more fundamental connection between MBH and the depth of the potential wells that just fail to prevent gas blow-out, due to feedback from rapid accretion during a quasar-phase. The potential wells in question were dominated by dark matter, and a general method is lacking to connect the stellar properties at z = 0 to properties of their dark matter halos, both at z = 0 and higher redshifts. The work presented here develops a method to make these connections self-consistently. Models of two-component spherical galaxies are used to establish scaling relations linking properties of spheroids at z = 0 (stellar masses, effective radii and velocity dispersions) to properties of the dark matter halo (virial masses and circular speeds), also at z = 0. These models are constrained by combining results from the literature connecting the masses and radii of dark matter halos to each other and stellar masses, with data samples for large, early-type galaxies. The z = 0 properties are then connected to dark matter properties at z > 0 by accounting for the halo redshift evolution. A critical SMBH mass prediction, with dependence on the maximum circular-speed in a protogalactic dark matter halo (MBH ∝ V 4 d,pk), is considered. Combining this with the scaling relations between z = 0 properties and halo properties at z > 0 transforms this theoretical relation into predictions for the observable SMBH correlations. A new prediction is also derived, extending on the MBH ∝ V 4 d,pk relation expected from momentum-driven outflows, allowing for the presence of stars and gas not tracing the dark matter. This new prediction is also compared to the observed correlations at z = 0.

In this thesis I present the culmination of my research into the phenomenon of AGN winds in the X-ray regime using the Suzaku X-ray telescope. There are two studies described in this thesis. In the first I perform a deep broad-band spectral analysis of radio-quiet quasar MR2251-178 and outline the evidence which suggests that its X-ray continuum is partially-covered by ionised gas along the line of sight, possibly in the form of a disc-wind. In the second study I perform a survey for Fe xxv Heα and Fe xxvi Lyα absorption lines in a large sample of 51 Suzaku-observed AGN (99 observations). These absorption lines are unambiguously detected in 40% of the sample (20/51 AGN), consistent with recent results from XMM-Newton, with peak and mean absorber parameters of log(NH/cm⁻²) ≈ 23 and log(ξ/erg cm s⁻¹) ≈ 4.5. Their velocities cover a continuous range, from v_out < 1500kms⁻¹ to ~ 100,000kms⁻¹, with a median of ~ 0.056 c. The winds are located on sub-parsec scales ( < 0.1 pc, typically), placing them in the vicinity of the inner accretion disc. A correlation analysis shows that more powerful AGN launch more powerful winds which implies their being accelerated by radiation pressure. Indeed, the overall energetics of the outflows are quantitatively consistent with continuum-driving via Compton-scattering, although a magnetic origin cannot be ruled out on the basis of the available data. I find that the mean kinetic power of the outflows is ~ 1%L_bol, suggesting a possible feedback effect in their host galaxies could be important. Finally, I show that the measured outflow velocity distribution bares a striking resemblance to one inferred using the MBH - δ* relation for local quiescent galaxies which suggests that the observed MBH - δ* relation may be an artefact of wind-induced feedback. Overall, these results are consistent with the view that highly-ionised FeK winds may represent an important addition to the currently held AGN paradigm, and further enforce the hypothesis that they may be important for galaxy evolution.

The aim of this thesis is to investigate uncertainties in the input physics of stellar models that are relevant for the evolution of stars and the related nucleosynthesis, in particular the s-process. Nuclear reaction rates and mixing prescriptions in particular can modify signi�cantly the yields of heavy elements in stellar models. The s-process, which is a slow neutron-capture process that can occur in massive stars and asymptotic giant branch (AGB) stars, is an important driver for uncertainty studies because the output yields of heavy nuclides in these astrophysical sites are sensitive to the interior conditions and the input physics. In this work, two uncertainties are considered. The �rst is the 12C + 12C nuclear reaction rate which, despite considerable experimental e�orts, remains uncertain at temperatures relevant for hydrostatic carbon burning in massive stars. We show that changes to this reaction rate a�ect the stellar structure and nucleosynthesis of massive stars and, consequently, the �nal yields. A comparison of these yields with the Solar system abundances enabled us to constrain the 12C + 12C reaction rate in the relevant temperature range. The second of these uncertainties is the treatment of convective-radiative interfaces in 1D stellar models, which are particularly important for modelling thermal pulses in AGB stars. The s-process during thermal pulses is sensitive to the treatment of mixing across convective-radiative interfaces. A possible link between full 3D hydrodynamics models of convective-radiative interfaces and 1D stellar models was investigated by considering a di�usion approximation. A technique for calculating di�usion coe�cients from the output of hydrodynamics models was developed and an exploration of the di�usive approach for convective-boundary mixing is presented, along with the successes and limitations of this approach.