A review of the classification of asteroids according to their orbital and physical properties is presented and the technique of numerical taxonomy is applied to catalogued optical data. The size distribution of minor bodies is of fundamental importance for theories of the origin and formation of the Solar System. Methods of diameter determination are reviewed with particular reference to the radiometric method. Thermal emission models of asteroids are essential for the reduction of infrared observations to obtain radiometric diameters and albedos. Various thermal models are described, with an emphasis on the assumptions made, and their limitations. The models are applied to observations in the 8-13?m region to examine possible variations of emissivity with wavelength, to remove the thermal component from reflection spectra in the 3-4?m region, and to determine the nature of the surface of the unusual asteroid (3200) 1983TB. The Infrared Astronomical Satellite (IRAS) was launched in 1983 to provide an all-sky survey in four infrared wavebands. In order to prevent detections of the thermal emission from moving objects from being lost, software was written to search the rejected survey data in near real-time. As well as detecting several hundred numbered asteroids and five known comets, two main belt asteroids, two Apollo asteroids, six comets and an infrared tail on comet Tempel-2 were discovered. A description of the moving object software and its implementation is presented, together with estimates of the selection effects and completeness of the search, and analysis of the data. The ground-based observations of the Apollo asteroid (3200) 1983TB do not support the cometary nucleus hypothesis inferred from its orbital characteristics. A preliminary analysis of some IRAS additional observations of asteroids is also presented.

This thesis investigates the evolution of galaxies as a function of look-back time, concentrating on early-type cluster galaxies. We demonstrate that selecting galaxies in the near-infrared produces samples that are representative of the galaxy population at intermediate and high redshift, and that such samples are likely to contain approximately the same proportion of all galaxy classes independently of z, avoiding the biases introduced by optical selection criteria. We have developed observing and data processing techniques using infrared arrays that yield high precision near-infrared photometry to very faint limits. Combining such data with optical photometry for the galaxy samples, we have been able to quantify the amount of colour evolution in early-type cluster galaxies up to redshifts z ~ 0.9.At z = 0.37 the mean colour-luminosity (c-L) relation for early-type cluster galaxies is compatible in slope and zero point with that of present-day ellipticals, indicating that the bulk of the stellar population at that epoch does not show any significant colour evolution. However, the scatter around the main c-L line is significantly larger than the observational errors, and distinctively non-Gaussian. We interpret this as evidence that a large fraction (~ 60%) of the early-type members have suffered a burst of star formation (involving ~ 10% of the galaxy mass) ~ 1 Gyr prior to the epoch of observation. In the redshift range 0.5 < z < 0.9, we detect systematic colour evolution with redshift in the red cluster galaxies. In particular, at z ~ 0.9 there are no galaxies as red as present day ellipticals at all wavelengths. The detected evolution is compatible with the passive ageing of stellar populations formed before z = 2. Superimposed on that, there is evidence for subsequent bursts of star formation happening on a substantial fraction of the cluster galaxies, but affecting only a small fraction of the total galaxy mass. We suggest this may be related to the Butcher-Oemler effect observed at lower redshifts. We did not detect significant amounts of galaxy luminosity evolution at 2µm, in contrast with the results for radio galaxies. We finally propose and test three new approaches to the study of normal field and cluster galaxies beyond z = 1: a study of gravitationally lensed galaxies, a search for galaxies producing clustered metallic absorption lines in QSOs and an infrared follow-up of ROSAT X-ray detected high redshift clusters.

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<p> Red giants with solar-like oscillations are astrophysical laboratories for probing the Milky Way. The <i>Kepler </i>Space Telescope revolutionized asteroseismology by consistently monitoring thousands of targets, including several red giants in eclipsing binaries. Binarity allows us to directly measure stellar properties independently of asteroseismology. In this dissertation, we study a subset of eight red giant eclipsing binaries observed by <i> Kepler</i> with a range of orbital periods, oscillation behavior, and stellar activity. Two of the systems do not show solar-like oscillations at all. We use a suite of modeling tools to combine photometry and spectroscopy into a comprehensive picture of each star's life. One noteworthy case is a double red giant binary. The two stars are nearly twins, but have one main set of solar-like oscillations with unusually low-amplitude, wide modes, likely due to stellar activity and modest tidal forces acting over the 171 day eccentric orbit. Mixed modes indicate the main oscillating star is on the secondary red clump (a core-He-burning star), and stellar evolution modeling supports this with a coeval history for a pair of red clump stars. The other seven systems are all red giant branch stars (shell-H-burning) with main sequence companions. The two non-oscillators have the strongest magnetic signatures and some of the strongest lifetime tidal forces with nearly-circular 20-34 day orbits. One system defies this trend with oscillations and a 19 day orbit. The four long-period systems (> 100 days) have oscillations, more eccentric orbits, and less stellar activity. They are all detached binaries consistent with coevolution. We find the asteroseismic scaling laws are approximately correct, but fail the most for stars that are least like the Sun by systematically overestimating both mass and radius. Strong magnetic activity and tidal effects often occur in tandem and act to suppress solar-like oscillations. These red giant binaries offer an unprecedented opportunity to test stellar physics and are important benchmarks for ensemble asteroseismology. Future asteroseismic studies should know they are excluding magnetically active stars and close binaries and be aware that asteroseismic masses and radii are both overestimated. </p>

<p> In this thesis, I explore two topics in exoplanet science. The first is the prevalence of Earth-size planets in the Milky Way Galaxy. To determine the occurrence of planets having different sizes, orbital periods, and other properties, I conducted a survey of extrasolar planets using data collected by NASA&rsquo;s <i>Kepler Space Telescope</i>. This project involved writing new algorithms to analyze <i>Kepler</i> data, finding planets, and conducting follow-up work using ground-based telescopes. I found that most stars have at least one planet at or within Earth&rsquo;s orbit and that 26% of Sun-like stars have an Earth-size planet with an orbital period of 100 days or less. </p><p> The second topic is the connection between the properties of planets and their host stars. The precise characterization of exoplanet hosts helps to bring planet properties like mass, size, and equilibrium temperature into sharper focus and probes the physical processes that form planets. I studied the abundance of carbon and oxygen in over 1000 nearby stars using optical spectra taken by the California Planet Search. I found a large range in the relative abundance of carbon and oxygen in this sample, including a handful of carbon-rich stars. I also developed a new technique called SpecMatch for extracting fundamental stellar parameters from optical spectra. SpecMatch is particularly applicable to the relatively faint planet-hosting stars discovered by <i>Kepler</i>.</p>

The criteria to be satisfied by a successful theory of the origin of the solar system are discussed before highlighting the difficulties of early two-body interaction theories. It is shown that these do not apply to Woolfson's capture theory which proposes that a light' diffuse protostar was tidally disrupted during a close encounter with the Sun and that the captured material might condense to form massive protoplanets. The smoothed particle hydrodynamic technique of Gingold & Monaghan is improved to provide a model for the computer simulation of stellar encounters. The protostar is replaced by a number of randomly distributed fluid elements, from which a density distribution may be recovered by a statistical technique. This distribution leads to a gravitational field and with a suitable thermodynamic model the pressure is determined at any point, enabling the dynamical evolution of the protostar to be simulated. The model is tested on a number of hydrostatic and hydrodynamic problems. A collapsing protostar is seen to be tidally disrupted during a close stellar encounter and the captured material moves quickly away from the Sun. This provides the optimal conditions for protoplanetary condensation. The effect of an initial protostellar rotation is also considered. It is shown that the quantity of material captured is critically dependent on the alignment of the protostellar spin axis to the orbital plane and, in an extreme case, might prevent the disruption of the protoster. The behaviour of a contracting protoplanet in the solar tidal field is investigated. It is shown that, despite severe distortion, it may well survive a perihelion passage without disruption and after further contraction may regain its spheroidal shape. Finally, a number of extensions to the capture theory are suggested.