Item consists of a digitized copy of an audio recording of a Vancouver Institute lecture given by Gordon Walker on November 22, 1975. Original audio recording available in the University Archives (UBC AT 398).

Over the last several years, a submillimetre astronomical polarizing Fourier Transform Spectrometer (FTS) has been developed for use at the James Clerk Maxwell Telescope (JCMT) located atop Mauna Kea, Hawaii. A new liquid3 He cooled dual polarization detector system has been carefully designed for use with this FTS to eliminate noise problems encountered with UKT14, the JCMT facility bolometric detector. The objective of this thesis is to evaluate and optimize the performance of the new detector system. The design of the detector system is discussed, and the noise performance of the system is evaluated. The system performance is determined from photmetric, classical B-I, and spectroscopic measurements. Compared to UKT14, the intrinsic bolometer noise is reduced by a factor of - 2. More importantly, the spectral signal to noise ratio is improved by a factor of - 10 due to the elimination of electrical pickup and microphone noise in the detector signal. / xiv, 156 leaves : ill. ; 28 cm.

The performance of existing and planned millimeter and submillimeter astronomical arrays is limited by fluctuations in the amount of atmosperic water vapor along the atenna's line of sight. Correcting the resulting phase distortion of the received signals is seen as a significant technological challenge. Measurements of the variation in the line-of-sight water vapor abundance at the level of 1 micron precipitable water vapor on a time scale of 1 second and at arbitrary antenna positions are required. This thesis describes the design of, and preliminary results obtained with, a water vapor monior operating at abundance at the level 1 micron precipitable water vapor on a time scale of 1 second and at arbitrary antenna positions are required. This thesis describes the design of, and preliminary results obtained with, a water vapor monitor operating at infrared wavelengths which shows considerable promise for this application. Improvements in, and future plans for, the second generation water vapor monitor currently under development are also discussed. / xiii, 167 leaves : ill. ; 28 cm.

This thesis unifies several studies, which all are dedicated to the subject of statistical data analysis in radio astronomy and radio astrophysics. Radio astronomy, like astronomy as a whole, has undergone a remarkable development in the past twenty years in introducing new instruments and technologies. New telescopes like the upgraded VLA, LOFAR, or the SKA and its pathfinder missions offer unprecedented sensitivities, previously uncharted frequency domains and unmatched survey capabilities. Many of these have the potential to significantly advance the science of radio astrophysics and cosmology on all scales, from solar and stellar physics, Galactic astrophysics and cosmic magnetic fields, to Galaxy cluster astrophysics and signals from the epoch of reionization. Since then, radio data analysis, calibration and imaging techniques have entered a similar phase of new development to push the boundaries and adapt the field to the new instruments and scientific opportunities. This thesis contributes to these greater developments in two specific subjects, radio interferometric imaging and cosmic magnetic field statistics. Throughout this study, different data analysis techniques are presented and employed in various settings, but all can be summarized under the broad term of statistical infer- ence. This subject encompasses a huge variety of statistical techniques, developed to solve problems in which deductions have to be made from incomplete knowledge, data or measurements. This study focuses especially on Bayesian inference methods that make use of a subjective definition of probabilities, allowing for the expression of probabilities and statistical knowledge prior to an actual measurement. The thesis contains two different sets of application for such techniques. First, situations where a complicated, and generally ill-posed measurement problem can be approached by assuming a statistical signal model prior to infer the desired measured variable. Such a problem very often is met should the measurement device take less data then needed to constrain all degrees of freedom of the problem. The principal case investigated in this thesis is the measurement problem of a radio interferometer, which takes incomplete samples of the Fourier transformed intensity of the radio emission in the sky, such that it is impossible to exactly recover the signal. The new imaging algorithm RESOLVE is presented, optimal for extended radio sources. A first showcase demonstrates the performance of the new technique on real data. Further, a new Bayesian approach to multi-frequency radio interferometric imaging is presented and integrated into RESOLVE. The second field of application are astrophysical problems, in which the inherent stochas- tic nature of a physical process demands a description, where properties of physical quanti- ties can only be statistically estimated. Astrophysical plasmas for instance are very often in a turbulent state, and thus governed by statistical hydrodynamical laws. Two studies are presented that show how properties of turbulent plasma magnetic fields can be inferred from radio observations.

Photonic crystal fibres (PCF) are a new generation of optical fibre that guide light via a periodic air-silica, photonic crystal structure instead of the more traditional step change in refractive index associated with traditional fibre. Careful design of the photonic structure causes the fibres to behave in interesting new ways and one of main aims of this thesis is to begin the investigation of the uses of PCF's in astronomy. Step index and large mode area (LMA) PCF's are introduced in Chapters 2 and 3, respectively. Chapter 4 then deals with the instrumental simplifications associated with the use of LMA PCF'ร in fibre stellar interferometry showing that up to four step index fibres and associated optics can be replaced with a single LMA fibre. One of the key features of LMA fibres, for astronomy, is that, unlike the step index fibre, the mode field size is independent of wavelength and the fibre can therefore be fed with a pupil image via a field lens. Chapter 5 investigates this important new parameter space showing that contiguous sampling using single mode fibres is now possible for the first time. Further, unlike the direct feed to the LMA fibre, maximised coupling over very large wavebands is now possible using just a single fibre. Chapter 6 deals with another new fibre technology in astronomy: Multi-mode fibre (MMF) to single-mode array (SMA) transitions. These fibre systems break out the modes of the multi-mode fibre into an array of single-mode fibres upon which Bragg gratings can be etched. The SMA is then refused into an output MMF resulting in a multimode device but with single-mode line suppression. The number of modes transmitted is numerically equal to the number of fibres in the SMA and the performance of these devices is investigated on a model telescope showing that only a few tens of modes is required to efficiently transmit either the J or н bands. Finally, Chapter 7 details the experimental investigation of fibre modal noise in high dispersion spectroscopy. This is a photometric error on a resolution element due to fibre modes interfering with each other at very high spectral dispersion. Worryingly, the results show that no current theory exists that can predict the performance of a fibre based high R spectrometer.

This thesis is concerned with the detection of pulsed TeV γ-rays from millisecond pulsars. These stars appear to include some very efficient producers of high energy particles, but the mechanisms by which they produce TeV γ-rays are still a matter of debate. After an introductory section, there is a brief description of the principles used in the atmospheric Cerenkov technique. The design and operation of the University of Durham atmospheric Cerenkov telescopes are reviewed. The main analysis techniques used to search for periodic signals are then described. The effects on periodic signals of binary motion of a source are discussed. These are a particularly important consideration for observations of millisecond pulsars, where high timing accuracy is required. One of the problems of detecting TeV sources is the cosmic ray background. A means of rejecting background events in TeV γ -ray telescopes is considered in chapter 5. The technique is developed for the Durham Mark III telescope. Substantial rejection of the cosmic ray background is achieved, with minimal loss of source events. The evolutionary scenarios which lead to the formation of millisecond pulsars are outlined. Two models for 7-ray emission are discussed briefly and applied to six known millisecond pulsars. Empirical results on these and two other pulsars are also presented. In particular, a detection of PSR 1855+09 is reported, and an upper limit to the flux from PSR 1957+20 is derived. All the empirical fluxes are compatible with the emission models, but the 'polar gap' model may be favoured. The final chapter summarises the results obtained and suggests some directions for future work on the 7-ray emission from millisecond pulsars.

217 leaves : ill. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.1972) from the Dept. of Physics, University of Adelaide

This thesis investigates techniques and algorithms for mitigating radio frequency interference (RFI) affecting radio astronomy observations. In the past radio astronomy has generally been performed in radio-quiet geographical locations and unused parts of the radio spectrum, including small protected frequency bands. The increasing use of the entire spectrum and global transmitters such as satellites are forcing the astronomy community to begin implementing active interference cancelling. The amount of harmful interference affecting observations will also increase as future instruments such as the Square Kilometre Array (SKA) are required to use larger bandwidths to reach up to 100 times the current sensitivity levels, and as spectral line observations require observing in bands licensed to other spectrum users. Particular attention is paid to interference cancellation algorithms which make use of reference beams. This has proven to be successful in removing interference from the contaminated astronomical data. Reference antenna cancellers are closely analysed, leading to filters and techniques that can offer improved RFI excision for some important applications. It is shown that pre- and post-correlation reference antenna cancellers give similar results, and an important aspect of the cancellers is the use of a second reference signal when the reference interference-to-noise ratio is low. These modified filters can theoretically offer infinite interference suppression in the voltage domain, equivalent to that of post-correlation interference cancellers, and their internal structure can offer an understanding of the residual RFI and added receiver noise components of a variety of reference antenna techniques. The effect of variable geometric delays is also considered and various filters are compared as a function of the geometric fringe rate.

Thesis (Ph.D. 1972) from the Dept. of Physics, University of Adelaide.

Thesis (Ph. D.)--PQ #3125068. / Includes bibliographical references.