Dissertations / Theses on the topic 'Astronomy'
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Woodard, Chelsea S. "Practical Astronomy." Thesis, University of North Texas, 2012. https://digital.library.unt.edu/ark:/67531/metadc149687/.
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This dissertation is a collection of poems preceded by a critical preface. The preface considers Anthony’s Hecht’s long poem, “The Venetian Vespers,” and the ways in which the temporally unsettled situation of the poem’s speaker parallels a problem facing narrative-meditative poets. The preface is divided into two main sections that explore divisions of this larger conflict. The first discusses the origins and effects of the speaker’s uprootedness in time, and the ways in which he tries to both combat and embrace this dislocation by temporarily losing himself in the immediacy of observing visual art. In this section I connect the dilemma of the speaker, who wishes to escape his memory by focusing outwards, to the dilemma of a representational poet who, despite his position towards the past, must necessarily confront or recollect memories and emotions in order to create authentic descriptions or characters. The second section focuses on the production and appreciation of artistic works (both visual and literary) and how the meaning, production and appreciation of beauty are inseparable from its existence within the physical limits of time. Here I discuss the significance of Hecht’s character who is surrounded with beauty yet describes himself as a person who only observes and does not create anything. Through this character, I argue that Hecht reveals a fundamental conflict that exists between artistic creation and chronological time, and that his poem embodies a particular and paradoxical view of beauty that resonates deeply with the motivations and struggles of writing poems.
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de, Val Borro Miguel. "Studies of Gas Disks in Binary Systems." Doctoral thesis, Stockholms universitet, Institutionen för astronomi, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-8337.
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There are over 300 exoplanets detected through radial velocity surveys and photometric studies showing a tremendous variety of masses, compositions and orbital parameters. Understanding the way these planets formed and evolved within the circumstellar disks they were initially embedded in is a crucial issue. In the first part of this thesis we study the physical interaction between a gaseous protoplanetary disk and an embedded planet using numerical simulations. In order to trust the results from simulations it is important to compare different methods. However, the standard test problems for hydrodynamic codes differ considerably from the case of a protoplanetary disk interacting with an embedded planet. We have carried out a code comparison in which the problem of a massive planet in a protoplanetary disk was studied with various numerical schemes. We compare the surface density, potential vorticity and azimuthally averaged density profiles at several times. There is overall good agreement between our codes for Neptune and Jupiter-sized planets. We performed simulations for each planet in an inviscid disk and including physical viscosity. The surface density profiles agree within about 5% for the grid-based schemes while the particle codes have less resolution in the low density regions and weaker spiral wakes. In Paper II, we study hydrodynamical instabilities in disks with planets. Vortices are generated close to the gap in our numerical models in agreement with the linear modal analysis. The vortices exert strong perturbations on the planet as they move along the gap and can change its migration rate. In addition, disk viscosity can be modified by the presence of vortices. The last part of this thesis studies the mass transfer in symbiotic binaries and close T Tauri binary systems. Our simulations of gravitationally focused wind accretion in binary systems show the formation of stream flows and enhanced accretion rates onto the compact component.
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Kuutmann, Andrej. "Photo-evaporation of Globulettes : Numerical hydrodynamic studies of photo-evaporating low-mass globules in the Rosette Nebula." Thesis, Stockholm University, Department of Astronomy, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-8354.
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In this work, the long-term evolution of globulettes, low-mass globules found in H II regions, is studied through numerical hydrodynamic simulations. It has been proposed by Gahm et al. (2007) that these clouds may form free-floating planetary mass objects due to shock compression, caused by heating from the intense UV radiation of the central OB star cluster. To address this possibility, lifetimes are calculated for three different 3D simulated cases, similar to globulettes found in the Rosette Nebula. A plane-parallel approximation of the radiation field is used, as well as an inhomogeneous initial density distribution. The ionizing radiation will cause the globulettes to photo-evaporate, creating a rocket acceleration effect from the mass ejected on the heated side of the cloud. For a typical globulette with an initial mass of 29.5 Jupiter masses a lifetime of 50 000 yrs is estimated. This estimate is compared to the analytical models of Mellema et al. (1998) and Bertoldi and McKee (1990) which suggest longer lifetimes; the discrepancy is attributed to fragmentation of the clouds in the numerical simulation, which is not adequately described by the models. Synthesized H-alpha images and lightcurves are presented, indicating that the bright rims of small clouds are only likely to be visible in dim parts of the Rosette Nebula. The morphology of simulated clouds generally agrees with observations. While the code does not include self-gravity, the gravitational stability of the clouds is studied indirectly. It is concluded that clouds in the planetary mass range are stable against gravitational collapse, from supporting thermal pressure alone, when in pressure equilibrium with the heated ionization front. However, gravity may play a significant role during the initial shock compression.
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Negrete, Regagnon Pedro. "Bispectral imaging in astronomy." Thesis, Imperial College London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307433.
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Belokurov, Vasily. "Variability surveys in astronomy." Thesis, University of Oxford, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.401024.
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Price, Gareth James. "Microchannel plates in astronomy." Thesis, University of Leicester, 2001. http://hdl.handle.net/2381/8638.
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This thesis describes both round-pore microchannel plates (MCPs) used in energetic pho¬ton and particle detectors and their square-pore offspring, micropore optics (MPOs), used to focus x-rays. A Monte Carlo electron raytracing software package is described that is used to predict the energy and angular distribution of electrons (EDOE and ADOE) in a microchannel electron multiplier's output charge cloud, including saturated operation. The model is shown to agree with experimental evidence. The addition of a micromachined electrostatic lens to the end of a microchannel is modelled and found to have no beneficial effects upon the EDOE and ADOE of the channel. The current state of the art planar and slumped 'lobster eye' square-packed MPOs are evaluated. The best focus (5' FWHM) from a large format (61mm x 56mm), small chan¬nel (10μm side length) planar MPO is reported, together with the observation of high energy (~50keV →65keV) x-ray focusing from large (500:1) aspect ratio channels. The alignment of many small lobster eye MPOs to create a large optic for the Lobster-ISS instrument is discussed and the alignment jig constructed for this purpose is used to measure the bias angles of a Lobster specification MPO. The bias angle is found to be 4 ± 1.5'. The concept of the microchannel conic approximation to the Wolter type I and II x- ray lenses is reviewed. A radially-packed twin MPO Wolter approximation is then tested, which while of poor quality, demonstrates true Wolter II imaging with a peak gain greater than unity. Currently proposed (UK) astronomical instruments that employ MPOs are then discussed in the light of the results from the current generation of MPOs.
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Van, Tonder Vereese. "Beamforming for radio astronomy." Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/96126.
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Thesis (MEng) -- Stellenbosch University, 2014.ENGLISH ABSTRACT: Beamforming is a technique used to combine signals from an array of antennas to effectively synthesize a single aperture and beam. In the Radio Astronomy community the technique is used to obtain a desirable beam pattern as well as to electronically point the beam of an array. Next generation radio telescopes such as the Square Kilometre Array (SKA) surpass current technology and will extensively make use of beamforming techniques. Various factors determine the output of a beamformer; however, given an array with a fixed configuration only the weights applied to the incoming signals affect the synthesized aperture and beam. Furthermore, the incoming data must be processed in real-time, at a rate equal to the input-output rate of the processor. Both the weighting function and the real-time implementation of beamforming, are the primary subjects of this thesis. In this thesis various deterministic weighting functions are investigated. The algorithms are implemented in a matlab program, serving as a simulation tool for investigating the techniques. The program is verified by comparing the expected theoretical outcomes to the simulated output. For the program the following functionalities are included: a steering technique, spectral weighting, Dolph-Chebychev, and the Least Square Error algorithm. Applications of these techniques is investigated and their prominence in the Radio Astronomy community is established. For the real-time beamformer implementation, the UniBoard platform configured with beamformer firmware, is investigated. This is important as the UniBoard is an excellent example of a beamformer implementation within the Radio Astronomy community. The architecture is used to emulate a linear array by implementing a python control script, where the output corresponded accurately with the expected theoretical values. The thesis also constitutes the design and implementation of a digital frequency domain beamformer on the ROACH board. This processing board is employed by the Karoo Array Telescope (KAT-7) in South Africa. This work is therefore important as it demonstrates a beamformer implementation on an architecture in use by the Radio Astronomy community. An antenna array is designed and built for the verification of the beamformer design. Results with a good degree of accuracy were obtained and where errors exist they are discussed.
AFRIKKANSE OPSOMMING: Bundelvorming is ’n tegniek waarmee die seine van ’n antenna samestelling gekombineer word om ’n enkele effektiewe stralingsvlak en stralingspatroon te sintiseer. In die Radio Astronomie gemeenskap word die tegniek gebruik om ’n gewenste stralingspatroon te sintiseer sowel as om die rigting van die patroon elektronies te beheer. Die Square Kilometre Array (SKA) is ’n toekomstige radioteleskoop en sal grootliks gebruik maak van bundelvorming tegnieke. Die uitset van bundelvormers word geaffekteer deur verskeie faktore, maar vir ’n gegewe samestelling is dit net die gewigsfunksies wat toegepas word op die inkomende seine wat die gesintiseerde patroon kan beheer. Verder moet die inkomende data verwerk word teen ’n tempo gelykstaande aan die inset-en-uitsetkoers van die verwerker. Die gewigsfunksie so wel as die implementasie van die bundelvormer is albei primêre onderwerpe van die tesis. ’n Verskeindenheid van deterministiese bundelvormingstegnieke sal ondersoek word in hierdie tesis. Die algoritmes is in ’n matlab program geïmplementeer vir simulasie doeleindes. Die program is geverifieër deur die uitset te vergelyk met die verwagte teoretiese waardes. Die program sluit die volgende funksies in: ’n rigting beheer algoritme, spektraalgewigte, Dolph-Chebychev, en die minste vierkantsfout algoritme. Hierdie tegnieke is van belang weens hul toepassing in die Radio Astronomie gemeenskap. Vir die implementasie van ’n bundelvormer is die UniBoard hardeware, geprogrameer in ’n bundelvormings modus, van gebruik gemaak. Hierdie aspek is belangrik omdat die Uni- Board ’n goeie voorbeeld van ’n geïmplementeerde bundelvormer in die Radio Astronomie gemeenskap is. Die UniBoard word gebruik om ’n lineêre samestelling te emuleer deur in python ’n beheer skrip te skryf, waar die uitset van die emuleerder akkuraat ooreenstem met die verwagte waardes. Die tesis behels ook die ontwerp en implementasie van ’n digitale frekwensiegebied bundelvormer op die ROACH platform. Hierdie verwerker word tans gebruik in die Karoo Array Telescope (KAT-7) in Suid-Afrika. Hierdie werk is dus belangrik omdat dit die implementasie van ’n bundelvormer op tegnologie wat huidiglik in die Radio Astronomie gemeenskap gebruik word demonstreer. Daarbenewens is ’n antenna samestelling ontwerp en gebou om die bundelvormer te verifieër. Die resultate is akkuraat tot ’n redelike mate. Waar daar ’n fout onstaan het word dit in die tesis bespreek.
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Harris, Robert James. "Photonic spectroscopy in astronomy." Thesis, Durham University, 2015. http://etheses.dur.ac.uk/10975/.
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This thesis investigates photonic spectroscopy and its use in astronomy. In chapter two the theory associated with both astronomical spectroscopy and photonic spectroscopy is shown. The convergence of the two in the field of astrophotonics is discussed along with existing work in the field. In chapter three models of the Integrated Photonic Spectrograph are created and compared like-for-like with existing instruments. The results suggest that the Integrated Photonic Spectrograph will be similar to existing instruments in terms of size and will require more detector pixels for a full instrument. In chapter four the modelling is extended, examining the areas where pho- tonic spectroscopy could show advatanges over conventional instrumentation. This is done by varying spectral resolution, telescope diameter, seeing and num- ber of objects sampled. The results show that the Integrated Photonic Spec- trograph will perform best when the telescope is close to the diffraction-limit, both in terms of size and number of detector pixels required. Science cases are presented for these areas. In chapter five different concepts for a redesigned Integrated Photonic Spec- trograph are presented and the advantages and disadvatanges of the variations are commented upon. The two that are chosen for development require the telescope Point Spread Function to be reformatted to a long slit. This device, which we have named the photonic-dicer is presented in chapter six. Its design, manufacture and testing is discussed both in the laboratory and on sky in conjunction with the CANARY adaptive optics system. Finally chapter seven presents our concluding remarks and discussions for future work.
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Du, Buisson Lise. "Machine learning in astronomy." Master's thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/15502.
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The search to find answers to the deepest questions we have about the Universe has fueled the collection of data for ever larger volumes of our cosmos. The field of supernova cosmology, for example, is seeing continuous development with upcoming surveys set to produce a vast amount of data that will require new statistical inference and machine learning techniques for processing and analysis. Distinguishing between real objects and artefacts is one of the first steps in any transient science pipeline and, currently, is still carried out by humans - often leading to hand scanners having to sort hundreds or thousands of images per night. This is a time-consuming activity introducing human biases that are extremely hard to characterise. To succeed in the objectives of future transient surveys, the successful substitution of human hand scanners with machine learning techniques for the purpose of this artefact-transient classification therefore represents a vital frontier. In this thesis we test various machine learning algorithms and show that many of them can match the human hand scanner performance in classifying transient difference g, r and i-band imaging data from the SDSS-II SN Survey into real objects and artefacts. Using principal component analysis and linear discriminant analysis, we construct a grand total of 56 feature sets with which to train, optimise and test a Minimum Error Classifier (MEC), a naive Bayes classifier, a k-Nearest Neighbours (kNN) algorithm, a Support Vector Machine (SVM) and the SkyNet artificial neural network.
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Utting, Muriel. "Astronomy in Western Australia." Thesis, Utting, Muriel (1993) Astronomy in Western Australia. Masters by Research thesis, Murdoch University, 1993. https://researchrepository.murdoch.edu.au/id/eprint/51548/.
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This thesis is devoted to a study of the origins and achievements of astronomers in Western Australia from 1829 to 1912. It addresses the questions about the role of astronomy in WA society, the reasons for the establishment of the Perth Observatory, and its achievements between 1896 and 1912. More widely, the thesis addresses the general question of the role of astronomy in our society and the contributions which astronomers have made to the development of Western Australia.
The first Premier of Western Australia, Sir John Forrest, persuaded his Government to build an Observatory, promising that it would house necessary services for the State, that is, timekeeping, meteorology, geodesy, tidal predictions and education services, to provide a scientific basis for society.
This service developed despite continuing opposition and interference from the Government and some sections of society. The thesis assesses the role of Lord Forrest and the Government Astronomer, W.E. Cooke, and his staff.
The thesis examines the historical context of the founding of the Observatory, the initial tasks set for it by Cooke and the extent to which these goals were achieved. Cooke's experience in establishing a modern Observatory in a fledgling society is examined in detail in order to understand the reasons for his resignation in 1912 and the nature of his achievements.
This study is intended to be both a scientific and social history of astronomy in Western Australia. It examines the scientific achievements of the Perth Observatory over its first 1 6 years in relation to its original objectives. The thesis also examines the social impact of the Observatory on WA society. The extent of its contribution is best assessed in the long-term where the benefits and costs of years of painstaking work can be more clearly understood.
This thesis is intended to provide an insight into the role of astronomy in society and the costs and benefits of major scientific institutions. By focussing on the origins and early development of astronomy in WA we can see how the interplay of political, economic and social factors influences the development of science. We can also see how long it takes for scientific projects to reach maturity and how a long-term perspective is required in order to assess their outcomes.
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Rautiainen, J. (Joona). "2D spectroscopy in astronomy." Bachelor's thesis, University of Oulu, 2019. http://jultika.oulu.fi/Record/nbnfioulu-201905282219.
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Abstract. 2D-spectroscopy in astronomy is defined as a technique where a spatially resolved electromagnetic spectrum is obtained over a two-dimensional field. In this paper the very basic principles of spectroscopy are briefly covered starting from the single slit concept via the Huygens principle and the Fraunhofer diffraction. The basic concept of a grating-based spectrograph is described. The connection between observed spectra, the chemical footprints and the underlying physical properties of the systems are briefly covered. The main IFU techniques used in the field of integral field spectroscopy are introduced. The basic ideas on how the data from the observed targets are produced and the wanted physical properties from the data are recovered are discussed. The work demonstrates the usage of 2D-spectroscopic data and its usefulness. The decay in the velocity dispersion profiles in the near central regions of galaxies known as sigma-drop is briefly introduced and a sample of 13 galaxies hosting a possible sigma-drop is analyzed via elliptical apertures. The radial profiles of each galaxy are extracted from given 2D-data connected to the kinematics of the sample galaxies. The radial profiles are then graphically presented with kinematic maps corresponding to the rotation velocity, the velocity dispersion, h₄ and h₃ profiles of the galaxy. Here the h₄ and h₃ are the amplitudes of the Gauss-Hermite series corresponding to the symmetric and asymmetric deviation from a Gaussian. The sample consists of only barred galaxies which could indicate star formation caused sigma-drops due to the bar-driven inflow of the gas to the central regions of the galaxies. Well-defined dust lanes are seen in ~70% of the sample showing a possible relation between the dust and the sigma-drops. There is no direct connection observed between the sigma-drops and the sizes of the galaxies.
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Carozzi, Tobia. "Radio waves in the ionosphere : Propagation, generation and detection." Doctoral thesis, Uppsala universitet, Institutionen för astronomi och rymdfysik, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-1184.
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We discuss various topics concerning the propagation, generation, and detec-tionof high-frequency (HF) radio waves in the Earth's ionosphere. With re-gardsto propagation, we derive a full wave Hamiltonian and a polarization evo-lutionequation for electromagnetic waves in a cold, stratified magnetoplasma.With regards to generation, we will be concerned with three experiments con-ducted at the ionosphere- radio wave interaction research facilities at Sura, Rus-siaand Tromsø, Norway. These facilities operate high power HF transmittersthat can inject large amplitude electromagnetic waves into the ionosphere andexcite numerous nonlinear processes. In an experiment conducted at the Surafacility, we were able to measure the full state of polarization of stimulatedelectromagnetic emissions for the first time. It is expected that by using thetechnique developed in this experiment it will be possible to study nonlinearpolarization effects on powerful HF pump waves in magnetoplasmas in the fu-ture.In another experiment conducted at the Sura facility, the pump frequencywas swept automatically allowing rapid, high-resolution measurements of SEEdependence on pump frequency with minimal variations in ionospheric condi-tions.At the Tromsø facility we discovered by chance a highly variable, pumpinduced, HF emission that most probably emanated from pump excited spo-radicE. Regarding detection, we have proposed a set of Stokes parametersgeneralized to three dimension space; and we have used these parameters in aninvention to detect the incoming direction of electromagnetic waves of multiplefrequencies from a single point measurement.
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Wilson, Richard Walter. "Synthesis imaging in optical astronomy." Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.281906.
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Junklewitz, Henrik. "Statistical inference in radio astronomy." Diss., Ludwig-Maximilians-Universität München, 2014. http://nbn-resolving.de/urn:nbn:de:bvb:19-177457.
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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.
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Corbett, Jason C. W. "Photonic crystal fibres in astronomy." Thesis, Durham University, 2006. http://etheses.dur.ac.uk/2661/.
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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.
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Brazler, Karen Tracy Susan. "TeV astronomy of millisecond pulsars." Thesis, Durham University, 1991. http://etheses.dur.ac.uk/5971/.
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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.
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Clayton, Martin John. "New detector technologies for astronomy." Thesis, University College London (University of London), 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.324635.
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Swinyard, Bruce Miles. "Polarimetry in gamma ray astronomy." Thesis, University of Southampton, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334541.
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Thompson, Nicholas Christopher. "RFI mitigation in radio astronomy." Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/86637.
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Thesis (MEng)--Stellenbosch University, 2014.ENGLISH ABSTRACT: Technical advances in electromagnetics, signal processing and processing power have led to a significant increase in sensitivity and accuracy in radio telescopes. With this increase in sensitivity, radio frequency interference (RFI) has become a much larger problem. The notable growth in wireless communication as well as self generated RFI has further escalated this problem. In order to utilise the full capabilities of modern radio telescopes, RFI mitigation is required on the captured signals. With the enormous data rates of modern radio telescopes, managing RFI has become increasingly difficult, and in order to utilise the full captured radio spectrum, more accurate RFI mitigation strategies will be necessary. The use of different RFI mitigation strategies is studied in the form of online and offline techniques. This includes Spectral Kurtosis, Spectral Flatness and the Var/SumThreshold method. The special case for RFI mitigation in timing pulsars will also be studied. These techniques are well known in the radio astronomy community; here, spectral kurtosis and spectral flatness will be implemented on the raw data as well as the post correlated data. System speed and accuracy will be the deciding factors when testing these methods as possible solutions to this problem.
AFRIKAANSE OPSOMMING: ‘n Toename in die sensitiwiteit van hedendagse radioteleskope kan toegedra word aan die tegniese bevordering in elktromagnetika en seinverwerking. Die toename in sensitiwiteit het egter tot die gevolg dat radiofrekwensiesteuring ‘n groter rol speel in hedendaagse radioteleskope. Die groei in die gebruik van radioverbindings asook die gevolge van self gei¨nduseerde radiofrekwensiesteuring dra ook verder by tot hierdie probleem. Radiofrekwensiesteuring matiging word toegepas op die opgevangde seine, om sodoende gebruik te maak van die volle kapasiteit van moderne radioteleskope. Die bestuur van radiofrekwensiesteuring word bemoeilik deur die groot hoeveelheid intydse data van die radioteleskope. Meer akurate radiofrekwensiesteuring matigingstegnieke word vereis om die bandwydte ten volle te hanteer. Daar word op ‘n aantal verskillende matingstegnieke gefokus. Hierdie tegenieke kan in twee kategorieë verdeel word, naamlik aanlyn- en aflyntegenieke. Onderafdelings van hierdie kategorieë sluit in: spektrale kurtose, spektrale matheid en “Var/SumThreshold”. Daar word ook na ‘n spesiale geval van radiofrekwensiesteuring matiging gekyk, in die opmeeting van tydsberekening-pulsars. Alhoewel hierdie tegnieke bekend is in die radioastronomie gemeenskap, word spektrale kurtose en spektrale matheid egter toegepas op die rou data sowel as postgekorreleerde data. Daar sal op stelsel spoed en akuratheid gefokus word, om vas te stel of hierdie metodes wel moontlike oplossings bied tot die probleem bespreek.
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COONEY, DANIELLE NICOLE. "THE ASTRONOMY OF A DANDELION." Thesis, The University of Arizona, 2016. http://hdl.handle.net/10150/612809.
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This thesis serves as a capstone of poetry for the University of Arizona Honors College Bachelor’s in Creative Writing. The Astronomy of a Dandelion is an exploration of the arts and sciences in conversation with one another, embodying both the personal and the technical throughout the manuscript. The originally proposed theme of astropoetry broadened into the use of astronomical imagery, metaphors, and other figurative language to describe neuroscientific issues of mental health, relationships of varying kinds, and the reconstruction of routine occurrences into something rather extra than ordinary. This is a manuscript that requires the sciences and the humanities to be mutually inclusive, accessible in different ways to myriad readers.
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Sen, Joydeep. "Astronomy in India, 1784-1876." Thesis, University of Warwick, 2010. http://wrap.warwick.ac.uk/34611/.
Full textAbstract:
This thesis aims to elucidate the changing forms of engagement between Europeans and Indians in relation to astronomy in India between 1784 and 1876. It seeks to trace the evolving contexts in which knowledge of astronomy was developed and to provide a nuanced characterisation of the resultant cognitive interface between Europeans and Indians, focusing in particular on Bengal and Bombay. The defining features of this period saw Europeans exploring the history of Indian astronomy, before establishing observatories and colleges to foster modern Western astronomy, while Indians turned to rethink how the history of Indian astronomy (and astrology) fitted with modern science. Yet while recent historiographical interventions have drawn attention to the more philosophical forms of engagement, this thesis contends that such a concentration has elided a much more practical engagement between Europeans and Indians in relation to modern (Western) astronomy in India. This engagement was not about a constant process of Indians rationalising participation in modern science, or looking backwards while moving forwards. In addition, it was premised more on collaborative and experiential constructions of knowledge, without express awareness of fixed "Western" or "Indian" paradigms. There was evidence of such engagement in the observatory and in the field, as well as in certain college settings, and in some parts of India more than others. However, racialised colonial institutions and attenuated educational schemas could at length hinder such possibilities, leaving the spotlight on the more philosophical forms of engagement. This thesis hence aims to address a lacuna in the history of science in colonial India by reappraising the significance of astronomy during these years. Through drawing on a range of written texts and physical objects in relation to astronomy, as well as on inter-disciplinary perspectives, it seeks to reflect the heterogeneous nature of the Indian intellectual climate in the colonial period.
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Harness, Anthony D. "High Contrast Astronomy with Starshades." Thesis, University of Colorado at Boulder, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10245089.
Full textAbstract:
One of the most important scientific discoveries to be had this century is the spectroscopic characterization of Earth-like exoplanets to determine the occurrence rate of worlds capable of supporting life and to potentially answer: are we alone in the universe? To accomplish these lofty goals requires an advancement in the technology to separate the overwhelming starlight from that of the exoplanet. I believe starshades are the key technology that will enable these discoveries within our lifetime. This dissertation work is a contribution to the advancement of starshade technology to put us on the path towards discovery.
In this dissertation I present a number of suborbital methods developed for testing small-scale starshades, which include a Vertical Takeoff Vertical Landing rocket, the surface of a dry lake bed, and the heliostat of a solar telescope. The results from our high contrast observations are used to validate the optical model I developed to conduct tolerance analyses that will drive future starshade designs. The results from testing a formation flying sensor on the VTVL rocket demonstrate the rocket’s potential for conducting starshade experiments in the stratosphere.
This dissertation (along with [Novicki, et al. (2016)]) presents the first astronomical observations with a starshade that provide photometric measurements of stars, previously unobserved in the visible spectrum, in the proximity of Vega. These observations led to the development of a visual feedback system for the heliostat that allows us to push farther in separation and inner working angle. These high contrast observations were made using a starshade in the most flight-like configuration (in terms of Fresnel number, inner working angle, and resolution) to date.
The results of this dissertation have helped demonstrate the effectiveness and practicality of starshades for starlight suppression and have outlined a path forward to further advance starshade technology through optical testing and high contrast astronomy.
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Bihi, Aniisa, and Johanna Granström. "Astronomy Software Integration with OpenSpace." Thesis, Linköpings universitet, Medie- och Informationsteknik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-173569.
Full textAbstract:
This thesis aimed to create a messaging protocol for OpenSpace to interoperate with other astronomy software. The goal was to create a messaging standard that was not language-dependent and could be implemented by any astronomy software. To establish an asynchronous communication between OpenSpace and connected software, the Transmission Control Protocol (TCP), threading, and Peer-To-Peer (P2P) were the techniques mainly used. TCP was used to achieve reliable communication between software connected to the network. The enabling of two-way communication was solved by threading. P2P was used as a network communication architecture to share resources between the connected software. By using Unicode characters expressed through UTF-8, the Unicode Standard was used to encode messages sent. The messages are structured by combinations of different sizes of bytes and are sent and received as binary strings. All messages contain a header and the data being sent. Different message types were created to specify which type of data is sent. The protocol works primarily between OpenSpace and Glue but is not limited to these software. The implementation serves as the basis of the messaging protocol for OpenSpace, where Glue represents future software integrations.
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O'Shaughnessy, Richard William Thorne Kip S. "Topics in gravitational wave astronomy /." Diss., Pasadena, Calif. : California Institute of Technology, 2004. http://resolver.caltech.edu/CaltechETD:etd-08052003-161044.
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Mitchell, Daniel Allan. "Interference Mitigation in Radio Astronomy." Thesis, The University of Sydney, 2004. http://hdl.handle.net/2123/693.
Full textAbstract:
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.
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Mitchell, Daniel Allan. "Interference Mitigation in Radio Astronomy." University of Sydney. Physics, 2004. http://hdl.handle.net/2123/693.
Full textAbstract:
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.
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Kloosterman, Jenna Lynn. "Heterodyne Arrays for Terahertz Astronomy." Diss., The University of Arizona, 2014. http://hdl.handle.net/10150/319878.
Full textAbstract:
The clouds of gas and dust that constitute the Interstellar Medium (ISM) within the Milky Way and other galaxies can be studied through the spectral lines of the atoms and molecules. The ISM follows a lifecycle in which each of its phases can be traced through spectral lines in the Terahertz (THz) portion of the electromagnetic spectrum, loosely defined as 0.3 - 3 THz. Using the high spectral resolution afforded by heterodyne instruments, astronomers can potentially disentangle the large-scale structure and kinematics within these clouds. In order to study the ISM over large size scales, large format THz heterodyne arrays are needed. The research presented in this dissertation focuses on the development of two heterodyne array receiver systems for ISM studies, SuperCam and a Super-THz (>3 THz) receiver. SuperCam is a 64-pixel heterodyne imaging array designed for use on ground-based submillimeter telescopes to observe the astrophysically important CO J=3-2 emission line at 345 GHz. The SuperCam focal plane stacks eight, 1x8 mixer subarrays. Each pixel in the array has its own integrated superconductor-insulator-superconductor (SIS) mixer and Low Noise Amplifier (LNA). In spring 2012, SuperCam was installed on the University of Arizona Submillimeter Telescope (SMT) for its first engineering run with 32 active pixels. A second observing run in May 2013 had 52 active pixels. With the outliers removed, the median double sideband receiver temperature was 104 K. The Super-THz receiver is designed to observe the astrophysically important neutral atomic oxygen line at 4.7448 THz. The local oscillator is a third-order distributed feedback Quantum Cascade Laser operating in continuous wave mode at 4.741 THz. A quasi-optical hot electron bolometer is used as the mixer. We record a double sideband receiver noise temperature of 815 K, which is ~7 times the quantum noise limit and an Allan variance time of 15 seconds at an effective noise fluctuation bandwidth of 18 MHz. Heterodyne performance is confirmed by measuring a methanol line spectrum. By combining knowledge of large array formats from SuperCam and quasi-optical mixers, initial tests and designs are presented to expand the single pixel 4.7 THz receiver into a quasi-optical 16-pixel array.
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Ely, Joshua J. "Society and Science: Ancient Astronomy." Digital Commons @ East Tennessee State University, 2012. https://dc.etsu.edu/honors/31.
Full textAbstract:
Astronomy is the oldest scientific field in human history. As such, it is linked heavily with Ancient History as a central part of understanding, scientific development and cultural appreciation in the world of antiquity. The goal of this thesis will be to investigate the importance of the ancient astronomers, their discoveries, the differences in cultural understandings of the universe due to environmental and political reasons, planets and the cosmos, and the impacts their discoveries had on the ancient world.
Primary sources will be various writings and documents by ancient astronomers and philosophers such as Eratosthenes, Hipparchus, Plato and the Pythagorean concept. Also to be consulted will be ancient documents that explain the cosmos and nature of this universe from the cultural aspect of the Egyptian, Maya, Mesopotamian, and Hellenistic civilizations. Secondary sources will a variety of modern historical and scientific writings about the history of astronomy. These will include Astronomy of the Ancients by Kenneth Brecher and Michael Feirtag, Ancient Egyptian Science by Marshall Clagett, and A History of The Ancient Mathematical Astronomy by Neugebauer. Also included will be modern sources that explain astronomical events and notions.
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Elmqvist, Söderlund Inga. "Taking possession of astronomy : Frontispieces and illustrated title pages in 17th-century books on astronomy." Doctoral thesis, Stockholms universitet, Konstvetenskapliga institutionen, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-38873.
Full textAbstract:
The thesis is a survey of 291 frontispieces and illustrated title pages in European books on astronomy from the 17th century. It is a quantitative and qualitative survey of how motifs are related to consumption, identification and display. Elements in the motifs related to factual content as opposed to those aimed to raise the perceived value of astronomy are distinguished. The quantitative study shows that astronomical phenomena (90 per cent) and scientific instruments (62 per cent, or as much as 86 per cent if only titles with illustrations occupying an entire page are considered) are the most common motifs to inform the reader of the genre. Besides these, a wide range of depicted features indicate the particularity of each title. Different means for raising the value of astronomy and its attributes are identified. The interplay of “real” or “credible” elements with fictional ones was used to attract attention, create positive associations and promote acquisition and reading. The motifs mainly promote delectation and erudition, although some attract attention through their deliberately enigmatic design and a few through fear. The survey determines prevalent settings (palaces, the theatre, gardens, the wilderness and the heavens), activities (skilful use of instruments, conversations or disputes), references to the ancients and heraldic components. They present both the self-image of astronomers at the time and ideal components that contain connotations of an enhanced reality. This self-image also contributed to the definition of normative values for astronomers in the 17th century. The affinities between painters and astronomers are examined. In addition, an analysis of descriptions of frontispieces is undertaken, which shows that the user of the book was expected to devote considerable time to the frontispiece in order to understand all of its particular features and that the illustrations were suitable for display and learned digression.
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Fisher, John Roger. "Astronomy and patronage in Hanoverian England : the work of James Bradley, third Astronomer Royal of England." Thesis, Imperial College London, 2004. http://hdl.handle.net/10044/1/8318.
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Gunnarsson, Marcus. "Gas Production in Distant Comets." Doctoral thesis, Uppsala University, The Uppsala Astronomical Observatory, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-2148.
Full textAbstract:
Molecular spectroscopy at radio wavelengths is a tool well suited for studying the composition and outgassing kinematics of cometary comae. This is particularly true for distant comets, i.e. comets at heliocentric distances greater than a few AU, where the excitation of molecules is inefficient other than for rotational energy levels. At these distances, water sublimation is inefficient, and cometary activity is dominated by outgassing of carbon monoxide.
An observing campaign is presented, where the millimeter-wave emission from CO in comet 29P/Schwassmann-Wachmann 1 has been studied in detail using the Swedish-ESO Submillimetre Telescope (SEST). Coma models have been used to analyse the spectra. The production of CO is found to have two separate sources, one releasing CO gas on the nuclear dayside, and one extended source, where CO is produced from coma material, proposed to be icy dust grains.
Radio observations of many molecules in comet C/1995 O1 (Hale-Bopp) have been carried out in a long-term international effort using several radio telescopes. An overview of the results is presented, describing the evolution of the gas production as the comet passed through the inner Solar system. Spectra recorded using the SEST, primarily of CO, for heliocentric distances from 3 to 11 AU are analysed in detail, also using coma models.
The concept of icy grains constituting the extended source discovered in comet 29P/Schwassmann-Wachmann 1 is examined by theoretical modelling of micrometre-sized ice/dust particles at 6 AU from the Sun. It is shown that that such grains can release their content of volatiles on timescales similar to that found for the extended source.
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Fidler, Chuck Gary. "Preservice elementary teachers learning of astronomy." Related electronic resource: Current Research at SU : database of SU dissertations, recent titles available full text, 2009. http://wwwlib.umi.com/cr/syr/main.
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Norton, Andrew John. "Galactic X-ray astronomy with EXOSAT." Thesis, University of Leicester, 1988. http://hdl.handle.net/2381/35751.
Full textAbstract:
The work presented in this thesis covers two topics: a study of Intermediate Polars (non- synchronously rotating magnetic cataclysmic variables) and a survey of the Galactic plane, both carried out with the EXOSAT observatory. The first part of the thesis describes a study of all the Intermediate Polars observed by EXOSAT. The X-ray light curves and spectra of each source are considered, with particular emphasis on the spin modulation. By treating the Intermediate Polars as an homogenous set of objects, a model for the accretion flow and emission region is developed in which the modulation is due to a combination of photo-electric absorption and occultation effects. The modulation seen can be explained in terms of a single, large emission area in the vicinity of the magnetic pole of the white dwarf. Further analysis is presented concerning the differences in the observed properties of GK Per, between outburst and quiescence. The results of these observations are interpretted in terms of a decreasing mass accretion rate and are shown to be in accord with the overall model presented. Finally the concept of the system equilibrium is discussed and used to determine the magnetic moments of the white dwarfs in each system from their spin periods and X-ray luminosities. The values found are shown to be significantly model dependent. The second part of the thesis concerns a survey of the Galactic plane. Scanning observations are used to produce a map of the medium energy X-ray emission and from this a catalogue of 70 sources is compiled. The source list includes many which were previously unidentified. Comments are made on the nature of the sources detected and on the two diffuse components (the Galactic Ridge and the Galactic Bulge) which were observed. Pointed observations were also made at seven of the previously unidentified sources which were detected in the map. These observations are analysed in an attempt to determine the type of object which is producing the emission, and also to gain some insight into possible origins of the two diffuse emission components.
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Bock, Douglas Carl-Johan. "Wide Field Aperture Synthesis Radio Astronomy." University of Sydney. Physics, 1998. http://hdl.handle.net/2123/377.
Full textAbstract:
This thesis is focussed on the Molonglo Observatory Synthesis Telescope (MOST), reporting on two primary areas of investigation. Firstly, it describes the recent upgrade of the MOST to perform an imaging survey of the southern sky. Secondly, it presents a MOST survey of the Vela supernova remnant and follow-up multiwavelength studies. The MOST Wide Field upgrade is the most significant instrumental upgrade of the telescope since observations began in 1981. It has made possible the nightly observation of fields with area ~5 square degrees, while retaining the operating frequency of 843 MHz and the pre-existing sensitivity to point sources and extended structure. The MOST will now be used to make a sensitive (rms approximately 1 mJy/beam) imaging survey of the sky south of declination -30°. This survey consists of two components: an extragalactic survey, which will begin in the south polar region, and a Galactic survey of latitudes |b| < 10°. These are expected to take about ten years. The upgrade has necessitated the installation of 352 new preamplifiers and phasing circuits which are controlled by 88 distributed microcontrollers, networked using optic fibre. The thesis documents the upgrade and describes the new systems, including associated testing, installation and commissioning. The thesis continues by presenting a new high-resolution radio continuum survey of the Vela supernova remnant (SNR), made with the MOST before the completion of the Wide Field upgrade. This remnant is the closest and one of the brightest SNRs. The contrast between the structures in the central pulsar-powered nebula and the synchrotron radiation shell allows the remnant to be identified morphologically as a member of the composite class. The data are the first of a composite remnant at spatial scales comparable with those available for the Cygnus Loop and the Crab Nebula, and make possible a comparison of radio, optical and soft X-ray emission from the resolved shell filaments. The survey covers an area of 50 square degrees at a resolution of 43" x 60", while imaging structures on scales up to 30'. It has been used for comparison with Wide Field observations to evaluate the performance of the upgraded MOST. The central plerion of the Vela SNR (Vela X) contains a network of complex filamentary structures. The validity of the imaging of these filaments has been confirmed with Very Large Array (VLA) observations at 1.4 GHz. Unlike the situation in the Crab Nebula, the filaments are not well correlated with H-alpha emission. Within a few parsec of the Vela pulsar the emission is much more complex than previously seen: both very sharp edges and more diffuse emission are present. It has been postulated that one of the brightest filaments in Vela X is associated with the X-ray feature (called a `jet') which appears to be emanating from the region of the pulsar. However, an analysis of the MOST and VLA data shows that this radio filament has a flat spectral index similar to another more distant filament within the plerion, indicating that it is probably unrelated to the X-ray feature.
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Gom, Bradley Gustav. "A cryogenic detector for submillimetre astronomy." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0026/MQ49144.pdf.
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Smith, Graeme John. "An infrared radiometer for millimeter astronomy." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/mq61045.pdf.
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Gom, Bradley Gustav, and University of Lethbridge Faculty of Arts and Science. "A cryogenic detector for submillimetre astronomy." Thesis, Lethbridge, Alta. : University of Lethbridge, Faculty of Arts and Science, 1999, 1999. http://hdl.handle.net/10133/102.
Full textAbstract:
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.
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Smith, Graeme John, and University of Lethbridge Faculty of Arts and Science. "An infrared radiometer for millimeter astronomy." Thesis, Lethbridge, Alta. : University of Lethbridge, Faculty of Arts and Science, 2000, 2000. http://hdl.handle.net/10133/122.
Full textAbstract:
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.
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Kennedy, Paul Robert. "Superconducting devices for millimetre-wavelength astronomy." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386169.
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Martindale, Adrian. "Novel X-ray instrumentation for astronomy." Thesis, University of Leicester, 2008. http://hdl.handle.net/2381/3964.
Full textAbstract:
This thesis describes experimental and theoretical work and technology development directed towards the next generation of X-ray astronomical instrumentation. A great heritage exists of instruments which are sensitive to X-rays which operate on board space based observatories. The next generation of such telescopes will take advantage of the rapid technology advancement of the last four decades of more accurately observe the universe and give greater insight into the objects within it, how they formed and how they will evolve. Chapters 2 and 3 describe the investigation of extremely high speed microchannel plate detectors capable of counting individual photons with a timing accuracy of a few tens of picoseconds (1 ps = 10-12s)at extremely high spatial resolution. Although many early X-ray astronomical instruments were based on MCP detectors, it is only recent manufacturing improvements which have enabled the production of such small pore diameters, enabling the unparalleled temporal and spatial resolution. Prospects for future application exist in fields as diverse as X-ray and ultraviolet astronomy and the life sciences. Chapters 4 and 5 report the testing of Microchannel plates as low mass X-ray optics where the development of square pore geometrics has made true imaging MCP telescopes possible. Two flight programs are identified as areas where such optics will provide tangible benefits: These are BepiColombo, a European mission to the planet Mercury which will contain the first ever imaging X-raytelescope on a planetary science mission and Lobster-ISS, a wide field of view telescope for X-ray astronomy which will provide coverage of, almost, the whole sky every 90 minute orbit. Testing reported herein finds that the manufacturing techniques are maturing to a point where they can exceed the <5 arcmin resolution required for these missions. Chapters 6 and 7 comprise a description of a completely novel X-ray polarimeter. For the past three decades, little or now progress has been made in the field of X-ray astrophysical polarimetry owing to the lack of suitable instrumentation, this is despite intense scientific interest in such measurements. A simple optical design for a polarimeter is made possible using highly ordered materials which exhibit dichroism at fixed, narrow energy bands, for the first time allowing simultaneous measurement of ALL astronomically pertinent observables. The areas of science influenced by these three areas of instrument development are shown to be very broad, including; astrophysics and cosmology, planetary science, life sciences, nano-science and even fundamental chemistry.
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Butcher, Jacqueline Anne. "Extragalactic X-ray astronomy with GINGA." Thesis, University of Leicester, 1994. http://hdl.handle.net/2381/35850.
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Ngongoni, Chipo Nancy. "Neural cross-correlation for radio astronomy." Master's thesis, University of Cape Town, 2010. http://hdl.handle.net/11427/11427.
Full textAbstract:
Includes abstract.Includes bibliographical references (leaves 56-62).
Correlation engines are essential elements of most signal processing systems. Areas of applicability include image processing, speech synthesis and analysis, high energy physics, wireless and mobile communication systems, spread spectrum communication systems and even prosthetics. Finding cost effective and computationally less intensive engines is the thrust of most research. Neural networks have also been used as aids in making complex tasks relatively easy to process.
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Manley, Jason Ryan. "A scalable packetised radio astronomy imager." Doctoral thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/15573.
Full textAbstract:
Includes bibliographical referencesModern radio astronomy telescopes the world over require digital back-ends. The complexity of these systems depends on many site-specific factors, including the number of antennas, beams and frequency channels and the bandwidth to be processed. With the increasing popularity for ever larger interferometric arrays, the processing requirements for these back-ends have increased significantly. While the techniques for building these back-ends are well understood, every installation typically still takes many years to develop as the instruments use highly specialised, custom hardware in order to cope with the demanding engineering requirements. Modern technology has enabled reprogrammable FPGA-based processing boards, together with packet-based switching techniques, to perform all the digital signal processing requirements of a modern radio telescope array. The various instruments used by radio telescopes are functionally very different, but the component operations remain remarkably similar and many share core functionalities. Generic processing platforms are thus able to share signal processing libraries and can acquire different personalities to perform different functions simply by reprogramming them and rerouting the data appropriately. Furthermore, Ethernet-based packet-switched networks are highly flexible and scalable, enabling the same instrument design to be scaled to larger installations simply by adding additional processing nodes and larger network switches. The ability of a packetised network to transfer data to arbitrary processing nodes, along with these nodes' reconfigurability, allows for unrestrained partitioning of designs and resource allocation. This thesis describes the design and construction of the first working radio astronomy imaging instrument hosted on Ethernet-interconnected re- programmable FPGA hardware. I attempt to establish an optimal packetised architecture for the most popular instruments with particular attention to the core array functions of correlation and beamforming. Emphasis is placed on requirements for South Africa's MeerKAT array. A demonstration system is constructed and deployed on the KAT-7 array, MeerKAT's prototype. This research promises reduced instrument development time, lower costs, improved reliability and closer collaboration between telescope design teams.
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Rubbo, Louis Joseph. "Gravitational wave astronomy using spaceborne detectors." Diss., Montana State University, 2004. http://etd.lib.montana.edu/etd/2004/rubbo/RubboL0805.pdf.
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Bock, Douglas Carl-Johan. "Wide Field Aperture Synthesis Radio Astronomy." Thesis, The University of Sydney, 1997. http://hdl.handle.net/2123/377.
Full textAbstract:
This thesis is focussed on the Molonglo Observatory Synthesis Telescope (MOST), reporting on two primary areas of investigation. Firstly, it describes the recent upgrade of the MOST to perform an imaging survey of the southern sky. Secondly, it presents a MOST survey of the Vela supernova remnant and follow-up multiwavelength studies. The MOST Wide Field upgrade is the most significant instrumental upgrade of the telescope since observations began in 1981. It has made possible the nightly observation of fields with area ~5 square degrees, while retaining the operating frequency of 843 MHz and the pre-existing sensitivity to point sources and extended structure. The MOST will now be used to make a sensitive (rms approximately 1 mJy/beam) imaging survey of the sky south of declination -30°. This survey consists of two components: an extragalactic survey, which will begin in the south polar region, and a Galactic survey of latitudes |b| < 10°. These are expected to take about ten years. The upgrade has necessitated the installation of 352 new preamplifiers and phasing circuits which are controlled by 88 distributed microcontrollers, networked using optic fibre. The thesis documents the upgrade and describes the new systems, including associated testing, installation and commissioning. The thesis continues by presenting a new high-resolution radio continuum survey of the Vela supernova remnant (SNR), made with the MOST before the completion of the Wide Field upgrade. This remnant is the closest and one of the brightest SNRs. The contrast between the structures in the central pulsar-powered nebula and the synchrotron radiation shell allows the remnant to be identified morphologically as a member of the composite class. The data are the first of a composite remnant at spatial scales comparable with those available for the Cygnus Loop and the Crab Nebula, and make possible a comparison of radio, optical and soft X-ray emission from the resolved shell filaments. The survey covers an area of 50 square degrees at a resolution of 43" x 60", while imaging structures on scales up to 30'. It has been used for comparison with Wide Field observations to evaluate the performance of the upgraded MOST. The central plerion of the Vela SNR (Vela X) contains a network of complex filamentary structures. The validity of the imaging of these filaments has been confirmed with Very Large Array (VLA) observations at 1.4 GHz. Unlike the situation in the Crab Nebula, the filaments are not well correlated with H-alpha emission. Within a few parsec of the Vela pulsar the emission is much more complex than previously seen: both very sharp edges and more diffuse emission are present. It has been postulated that one of the brightest filaments in Vela X is associated with the X-ray feature (called a `jet') which appears to be emanating from the region of the pulsar. However, an analysis of the MOST and VLA data shows that this radio filament has a flat spectral index similar to another more distant filament within the plerion, indicating that it is probably unrelated to the X-ray feature.
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Lindley, Emma. "Multicore fibre Bragg gratings for astronomy." Thesis, The University of Sydney, 2017. http://hdl.handle.net/2123/16682.
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Astrophotonics is the discipline of applying photonic technology in instrumentation to address problems in astronomy and astrophysics. Photonic devices known as fibre Bragg gratings (FBGs) can be used as highly selective filters for removal of unwanted light prior to dispersion in a spectrograph. It has been shown that FBGs are well suited to the problem of removing atmospheric molecular emission lines from ground-based near- infrared observations. This thesis describes the development of a new generation of FBGs for this purpose, inscribed within multi-core fibres (MCFs) which contain multiple single- mode cores within one cladding. A new component, the polished capillary tube (PCT), was modelled, fabricated and tested; results showed that this was an effective device for improving the uniformity of gratings within MCFs. Following this a protocol for temperature tuning of gratings relative to one another was developed and tested. Finally, this thesis describes the development of a new instrument for inscribing gratings in fibres. When MCF technology reaches maturity, they will be used in astronomical instruments for atmospheric suppression, and will also have applications wherever photonics is used.
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Lesser, Michael Patrick. "Charge-coupled device optimizations for astronomy." Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/184387.
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In the past decade, charge-coupled devices (CCDs) have rapidly become the astronomical imaging detector of choice for the visible and near-IR spectral regions. There are, however, several problems which have greatly reduced the availability of sufficient quality CCDs to the astronomical community. These include the low blue and ultraviolet quantum efficiency of thick devices, the lack of properly thinned devices, warped imaging surfaces, interference fringing, and the small size of the detectors themselves compared to telescope focal planes. This dissertation presents methods which can be used to optimize CCDs obtained from various manufacturers for astronomical observations. A new thinning technique which produces an optically flat surface across an entire CCD is demonstrated. A mounting technique which maintains a flat and stable imaging surface for thinned devices by bonding the CCD backside against a transparent glass support substrate is also demonstrated. Bump bonding of CCDs onto a silicon support before thinning is discussed as a future mounting/thinning technique. The design of antireflection coatings for the near-UV through near-IR spectral regions is explained and demonstrated on silicon diodes, allowing quantum efficiencies as high as 90% to be obtained. The reduction of interference fringing amplitudes by as much as 70% in the red and near-IR with AR coatings is also discussed. And finally, the design of CCD focal plane mosaics using the optimization techniques presented is discussed.
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Chlench, Kathrin. "Johannes von Gmunden deutsch : der Wiener Codex 3055 : deutsche Texte des Corpus astronomicum aus dem Umkreis von Johannes von Gmunden /." Thesis, Wien : Fassbaender, 2007. http://deposit.d-nb.de/cgi-bin/dokserv?id=2942867&prov=M&dok_var=1&dok_ext=htm.
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Ringvall, Jonas, and Malin Kvist. "Jämförbarhet vs. innebörd och form." Thesis, Uppsala University, Department of Business Studies, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8988.
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de, Cruz Pérez Javier. "Implications of Dynamical Dark Energy in the expansion of the Universe and the Structure Formation." Doctoral thesis, Universitat de Barcelona, 2021. http://hdl.handle.net/10803/671792.
Full textAbstract:
En aquesta tesi s’estudien diferents models cosmològics, tots ells caracteritzats per considerar, de manera efectiva, una lleu evolució temporal de l’Energia Fosca, en contrast amb l’actual model estàndard de la cosmologia. El terme Energia Fosca s’utilitza per fer referència a una misteriosa forma d’energia que sembla impregnar tots els racons del Univers i que provoca que les galàxies s’allunyin les unes de les altres. El ritme predit d’expansió del Univers varia d’un model a un altre així com la quantitat d’estructura observada i la distribució d’aquesta.
Degut al bon moment de la cosmologia observacional tenim a la nostre disposició una gran quantitat de dades que ens permeten posar a prova els diferents models existents. Un exemple d’aquests models, seria el Running Vacuum Model (RVM), que ha estat estudiat en detall en aquesta tesi i que considera una expressió per la densitat d’energia del buit motivada en el context de les Teories Quàntiques de Camp. Un altre exemple de models cosmològics serien els anomenats models de camp escalar que suposen que l’equació d’estat de l’Energia Fosca, en el moment present, és lleugerament diferent del valor predit pel model estàndard.
No noées s’han considerat models acomodats dins del marc de la teoria de la Relativitat General, sinó que també s’han estudiat les prediccions teòriques del model presentat per Brans i Dicke al 1961 i que resulta ser el primer intent d’extensió de la teoria d’Einstein. El model de Brans i Dicke està caracteritzat pel fet que la interacció gravitatòria està no només mediada per un camp tensorial, sinó també per un camp escalar.
Les prediccions teòriques dels diferents models estudiats, tant a nivell de background com a nivell de pertorbacions, han sigut contrastades amb les mes recents dades cosmològiques revelant que l'anteriorment esmentada evolució temporal de l’Energia Fosca ajuda a rebaixar, de manera considerable, algunes de les tensions que afecten al model estàndard. La comparació teoria-observacions s’ha dut a terme mitjançant una rigorosa metodologia que involucra diferents eines estadístiques. Per tant les conclusions obtingudes al llarg d’aquesta tesi es basen en un procés robust i en un estudi detallat dels diferents models cosmològics considerants.The high quality observations performed during the last two decades, have allowed to demonstrate, with high confidence range, that the Universe is in expansion and to be more precise in accelerated expansion. In order to explain the accelerated evolution the name of dark energy was coined. It refers to a some mysterious form of diffuse energy presumably permeating all corners of the Universe as a whole. We may say that the canonical picture of our Universe defined in the framework of General Relativity, whose field equation were found by Einstein in 1917, is built upon the assumption that the observed acceleration is caused, in fact, by a rigid cosmological constant term denoted by Λ. Thanks to the aforementioned cosmological measurements, we have been able to pin down its value to an impressive level. Dark energy is not the only element, beyond the conventional baryons and photons, required by the observations since we also need large amounts of what is commonly call as dark matter. We call such an overall picture of the Universe the “concordance (or standard) cosmological model” or simply ΛCDM. Therefore, we attribute the observed accelerated expansion of the Universe to the existence of a repulsive force, exerted by the Λ term, which works against the attractive gravitational force and tends to push the clusters of galaxies apart at a speed continuously increasing with the cosmic expansion. Throughout this thesis a wide variety of models, beyond the standard model have been studied. The corresponding analyses have been carried out by studying in detail the theoretical predictions at the background and perturbation level, with the purpose of testing them with the large amount of cosmological data which we currently we have access to. The ultimate goal is to see if we can detect signals of new physics that help to alleviate some of the tensions that affect the ΛCDM. The concordance model, has remained robust and unbeaten for a long time since it is roughly consistent with a large body of cosmological data. Because of this fact, it is not reasonable to look for models with a very different behaviour than the ΛCDM, but to study models that exhibit small departures with respect to the standard model in key aspects. We have studied the Running Vacuum Models (RVM) in depth. They are characterized by having a time-evolving vacuum energy density, whose functional expression is motivated in the context of Quantum Field Theory in curved space-time. It is fundamental that its expression contains a constant term, which mimics the standard behaviour in order to first generate the transition from a decelerated to an accelerated Universe and to ensure that the fit of the structure formation data is not ruined. We have also studied the Peebles & Ratra model, which is a particularly successful scalar field model φCDM for which the potential takes the form V (φ) ∼ φ−α . The dimensionless parameter α encodes the extra degree of freedom that this model has with respect to the standard model. It is found to be small and positive, therefore V (φ) can mimic and approximate cosmological constant that is decreasing slowly with time. In the late Universe the contribution of the scalar field, φ, surfaces over the matter density, thus becoming the dominant component. Not all the models studied are motivated within a theoretical framework, since we have also considered some interesting phenomenological approaches. Last but not least, at the end of the thesis the Brans & Dicke (BD) gravity model was studied in detail. The main feature of this model is that the Newtonian constant coupling GN is replaced by a dynamical scalar field G(t) = 1/ψ(t), coupled to the curvature. As a consequence the gravitational interaction is not only mediated by the metric field, as in the General Relativity case but also for the aforementioned scalar field ψ. The obtained results clearly point out to an interesting conclusion, those models which consider an effective time-evolving dark energy are able to alleviate some of the tensions affecting the ΛCDM. Among the different tensions there are two that stand out, namely the σ8 -tension and the H0-tension.