University, Diss., 2003--Bonn.

University, Diss., 2004--Bonn.

University, Diss., 2004--Bonn.

This thesis presents the design and development of a process to model Very Long Base Line Interferometry (VLBI) aperture synthesis antenna arrays. In line with the Auckland University of Technology (AUT) Institute for Radiophysics and Space Research (IRSR) aims to develop the knowledge, skills and experience within New Zealand, extensive use of existing radio astronomical software has been incorporated into the process namely AIPS (Astronomical Imaging Processing System), MIRIAD (a radio interferometry data reduction package) and DIFMAP (a program for synthesis imaging of visibility data from interferometer arrays of radio telescopes). This process has been used to model various antenna array configurations for two proposed New Zealand sites for antenna in a VLBI array configuration with existing Australian facilities and a passable antenna at Scott Base in Antarctica; and the results are presented in an attempt to demonstrate the improvement to be gained by joint trans-Tasman VLBI observation. It is hoped these results and process will assist the planning and placement of proposed New Zealand radio telescopes for cooperation with groups such as the Australian Long Baseline Array (LBA), others in the Pacific Rim and possibly globally; also potential future involvement of New Zealand with the SKA. The developed process has also been used to model a phased building schedule for the SKA in Australia and the addition of two antennas in New Zealand. This has been presented to the wider astronomical community via the Royal Astronomical Society of New Zealand Journal, and is summarized in this thesis with some additional material. A new measure of quality (“figure of merit”) for comparing the original model image and final CLEAN images by utilizing normalized 2-D cross correlation is evaluated as an alternative to the existing subjective visual operator image comparison undertaken to date by other groups. This new unit of measure is then used in the presentation of the results to provide a quantative comparison of the different array configurations modelled. Included in the process is the development of a new antenna array visibility program which was based on a Perl code script written by Prof Steven Tingay to plot antenna visibilities for the Australian Square Kilometre Array (SKA) proposal. This has been expanded and improved removing the hard coded fixed assumptions for the SKA configuration, providing a new useful and flexible program for the wider astronomical community. A prototype user interface using html/cgi/perl was developed for the process so that the underlying software packages can be served over the web to a user via an internet browser. This was used to demonstrate how easy it is to provide a friendlier interface compared to the existing cumbersome and difficult command line driven interfaces (although the command line can be retained for more experienced users).

This thesis presents the design and development of a process to model Very Long Base Line Interferometry (VLBI) aperture synthesis antenna arrays. In line with the Auckland University of Technology (AUT) Institute for Radiophysics and Space Research (IRSR) aims to develop the knowledge, skills and experience within New Zealand, extensive use of existing radio astronomical software has been incorporated into the process namely AIPS (Astronomical Imaging Processing System), MIRIAD (a radio interferometry data reduction package) and DIFMAP (a program for synthesis imaging of visibility data from interferometer arrays of radio telescopes). This process has been used to model various antenna array configurations for two proposed New Zealand sites for antenna in a VLBI array configuration with existing Australian facilities and a passable antenna at Scott Base in Antarctica; and the results are presented in an attempt to demonstrate the improvement to be gained by joint trans-Tasman VLBI observation. It is hoped these results and process will assist the planning and placement of proposed New Zealand radio telescopes for cooperation with groups such as the Australian Long Baseline Array (LBA), others in the Pacific Rim and possibly globally; also potential future involvement of New Zealand with the SKA. The developed process has also been used to model a phased building schedule for the SKA in Australia and the addition of two antennas in New Zealand. This has been presented to the wider astronomical community via the Royal Astronomical Society of New Zealand Journal, and is summarized in this thesis with some additional material. A new measure of quality (“figure of merit”) for comparing the original model image and final CLEAN images by utilizing normalized 2-D cross correlation is evaluated as an alternative to the existing subjective visual operator image comparison undertaken to date by other groups. This new unit of measure is then used in the presentation of the results to provide a quantative comparison of the different array configurations modelled. Included in the process is the development of a new antenna array visibility program which was based on a Perl code script written by Prof Steven Tingay to plot antenna visibilities for the Australian Square Kilometre Array (SKA) proposal. This has been expanded and improved removing the hard coded fixed assumptions for the SKA configuration, providing a new useful and flexible program for the wider astronomical community. A prototype user interface using html/cgi/perl was developed for the process so that the underlying software packages can be served over the web to a user via an internet browser. This was used to demonstrate how easy it is to provide a friendlier interface compared to the existing cumbersome and difficult command line driven interfaces (although the command line can be retained for more experienced users).

University, Diss., 2004--Bonn.

Submitted by Romulus Lima (romulus.lima@ufpe.br) on 2015-03-04T18:53:33Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) DISSERTAÇÃO Wanessa de Oliveira Souza.pdf: 4794560 bytes, checksum: 5ba5772b8bf5effa94d0408446df468d (MD5) / Made available in DSpace on 2015-03-04T18:53:33Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) DISSERTAÇÃO Wanessa de Oliveira Souza.pdf: 4794560 bytes, checksum: 5ba5772b8bf5effa94d0408446df468d (MD5) Previous issue date: 2013-08-29 / Reuni, CAPES, CNPQ / Há cerca de 220 milhões de anos os continentes vêm afastando-se uns dos outros. Esse fenômeno se explica a partir da teoria da deriva continental, complementada pela teoria da tectônica de placas, onde se acreditava que estruturas rígidas como as placas litosféricas, eram capazes de transmitir tensões em longas distâncias sem causar deformações internas. Desta forma, devido ao movimento das placas e como consequência a deriva dos continentes, as estações a eles pertencentes também vêm se movendo em relação a um referencial geocêntrico. Considerando que, com a evolução tecnológica e as facilidades geradas no tratamento de dados globais, a Geodésia ganhou um dinamismo sem precedentes, incorporando em seus métodos de posicionamento, atualizações periódicas dos referencias globais, como exemplo, as estruturas iniciadas pelos ITRF’s de 1988 até o de 2008. Do ponto de vista científico, não há problema nenhum quanto ao dinamismo das estruturas geodésicas, mas do ponto de vista prático e legal, tal dinamismo gera alguns inconvenientes, que podem ser resolvidos pelo conhecimento e modelagem adequada para as transformações a serem executadas. No tocante ao deslocamento da placa tectônica Sul-americana, alguns modelos de velocidade vêm sendo utilizados desde a virada do milênio, entre eles: NNR-NUVEL-1A; APKIM2000; APKIM8.8; ITRF2000; COSTA, SANTOS e GEMAEL (2003); PEREZ, MONICO e CHAVES (2003); e VEMOS2009. Como o Sistema Geodésico Brasileiro, SIRGAS2000, oficializado pela RPR 01 (IBGE), de 25 de fevereiro de 2005, passou a utilizar a época de referência 2000,4, então o posicionamento atual de medidas podem precisar de uma redução de 13 anos. Confrontando os modelos citados e gerando as discrepâncias, analisaram-se na ordem milimétrica e também na ordem centimétrica as equivalências dos modelos para o território brasileiro. O modelo VEMOS2009 atualmente utilizado pelo IBGE no serviço PPP online foi tomado como referência padrão, na análise comparativa. Além desses, com base no processamento semanal do SIRGAS-CON (http://www. sirgas.org/index.php?id=153) dos anos de 2008 a 2011 de algumas estações da RBMC, cuja geometria permitisse uma amostra significativa da placa sul-americana (SOAM) e também se aproveitando de dados de duas estações VLBI (Very Long Baseline System) sobre a placa SOAM; uma (Ft) localizada na cidade de Fortaleza – CE, Brasil e a outra (TIGO) localiza em Concepción no Chile, processadas pelo IVS (International VLBI service for Geodesy and astrometry), pôde-se gerar um modelo atual de velocidades e participar das análises comparativas. Os processamentos foram realizados com os módulos: modeloSOAM@ versão 2013.07.08 e ModelTectonica@2013.07.07 do software AstGeo- Top. Os resultados mostraram a possibilidade de utilizar vários dos modelos citados quando a discrepância puder ser até de 5 cm em 13 anos, mas ficou reduzida a algumas regiões do Brasil e a três dos modelos quando a discrepância não puder ultrapassar a 1cm em 13 anos.

Les Noyaux Actifs de Galaxies (AGN) se situent au centre de galaxies extrêmement lointainesdont la luminosité provient de l’interaction d’un trou noir central supermassif et d’undisque d’accrétion. Il en résulte l’éjection à des vitesses relativistes de jets de matière collimatés.L’interférométrie à très longue base (VLBI) permet, grâce aux très grandes résolutionsatteintes, d’observer finement la structure de ces jets et de déterminer très précisément laposition astrométrique des objets. En raison de leur distance, les AGN ne présentent pas demouvements propres, ce qui les rend idéaux pour la construction de systèmes de référenceultra-précis et très stables.Des instabilités en position de quelques centaines de microsecondes d’arc, généralementimputées aux variations de la structure des jets, sont toutefois souvent observées sur des échellesde temps de quelques mois à quelques années. Le travail présenté ici étudie le lien entre les deuxphénomènes de façon statistique. Sur la base d’observations VLBI régulières conduites entre1994 et 2003, nous comparons l’évolution de la position astrométrique et de la structure des jetspour un échantillon de 68 AGN sur une période de 10 ans. Les résultats de l’étude indiquent quela corrélation entre les deux phénomènes existe mais n’est pas aussi forte qu’attendue. Le travailest complété par une simulation des effets causés sur la trajectoire des jets par la précessiondu disque d’accrétion ainsi que par la présence d’un système binaire de trous noirs. Appliquéeau cas de la source 1308+326, l’étude montre que l’amplitude de ces effets est compatible avecles oscillations de la trajectoire observées en VLBI. / Active Galactic Nuclei (AGN) are located in the center of extremely distant and bright galaxies. Their luminosity comes from the interaction between a super-massive central blackhole and an accretion disk, producing a relativistic collimated jet of matter. Thanks to the extremely high resolution achieved by Very Long Base line Interferometry (VLBI), the jet structure may be studied in detail, while the astrometric position of the AGN is determined with ahigh accuracy. Because of their location at cosmological distances, no proper motions are detected for those objects, making them ideal fiducial points for building highly-precise celestial reference frames.Instabilities up to a few hundreds of micro arc seconds are yet often observed in astrometricpositions on time scales from months to years. This is generally thought to be caused by theevolution of source structure. The study presented here investigates the correlation between the two phenomena on a statistical basis. Based on regular VLBI observations conducted between1994 and 2003, astrometric position variations and source structure evolution are compared fora sample of 68 AGN over a period of 10 years. The results indicate that a correlation between the two phenomena does exist but it is not as strong as expected. Additionally, a simulation of the effects caused by the precession of the accretion disc and the potential presence of abinary black hole in the center of the AGN is presented. Applied to the source 1308+326, the simulation shows that the magnitude of the effects is consistent with the oscillations of the jet trajectory observed on VLBI scale.

Köln, University, Diss., 2008.

OH Megamasers (OHMs) generally appear in luminous infrared regions i.e. merging galaxies. In this study we assume that OHMs may not be represented by their association with star formation solely, because of the possibility of a compact AGN source in the merging galaxies. In fact, previously classified starburst galaxies where OHMs are found are now optically observed as AGN. OHMs may also serve as a reasonable criterion for the evolutionary stage of the merger. This project focuses on observations from a multi-frequency analysis of merging regions with known OHMs. Optically, Hα and BVRI filters provided an environmental perspective of the "masing" components. In the radio, 18-cm data was used to determine the structure and position of the OHM. We studied the source IIZw096 and compared our results with two familiar OHM sources. We were able to look at each source at high radio resolutions and compare the structure and classification of each.