Showing papers by "Richard Dodson published in 2008"
Commonwealth Scientific and Industrial Research Organisation1, University of Calgary2, Swinburne University of Technology3, York University4, Durham University5, University of Sydney6, University of Colorado Boulder7, University of Tasmania8, University of California, Berkeley9, University of Adelaide10, Laval University11, McGill University12, Herzberg Institute of Astrophysics13, California Institute of Technology14, La Trobe University15, University of Toronto16, University of British Columbia17, University of Western Australia18, Curtin University19
TL;DR: The Australian SKA Pathfinder (ASKAP) as mentioned in this paper is aimed squarely in this frequency range, and achieves instantaneous wide-area imaging through the development and deployment of phase-array feed systems on parabolic reflectors.
Abstract: The future of cm and m-wave astronomy lies with the Square Kilometre Array (SKA), a telescope under development by a consortium of 17 countries. The SKA will be 50 times more sensitive than any existing radio facility. A majority of the key science for the SKA will be addressed through large-area imaging of the Universe at frequencies from 300 MHz to a few GHz. The Australian SKA Pathfinder (ASKAP) is aimed squarely in this frequency range, and achieves instantaneous wide-area imaging through the development and deployment of phase-array feed systems on parabolic reflectors. This large field-of-view makes ASKAP an unprecedented synoptic telescope poised to achieve substantial advances in SKA key science. The central core of ASKAP will be located at the Murchison Radio Observatory in inland Western Australia, one of the most radio-quiet locations on the Earth and one of the sites selected by the international community as a potential location for the SKA. Following an introductory description of ASKAP, this document contains 7 chapters describing specific science programmes for ASKAP. In summary, the goals of these programmes are as follows: The combination of location, technological innovation and scientific program will ensure that ASKAP will be a world-leading radio astronomy facility, closely aligned with the scientific and technical direction of the SKA. A brief summary chapter emphasizes the point, and considers discovery space.
406 citations
Japan Aerospace Exploration Agency1, National Radio Astronomy Observatory2, University of Turku3, Graduate University for Advanced Studies4, Australia Telescope National Facility5, University of Calgary6, Joint Institute for VLBI in Europe7, Chinese Academy of Sciences8, University of Tasmania9, Swinburne University of Technology10, Curtin University11, Jet Propulsion Laboratory12, Whittier College13, Purdue University14, Konkoly Thege Miklós Astronomical Institute15, National University of Cordoba16
TL;DR: In this article, the authors presented images and models for the remaining 140 sources not included in the third paper in the series, which contained 102 sources, and the brightness temperature distributions for all of the sources in the VSOP AGN survey were discussed.
Abstract: In 1997 February, the Japanese radio astronomy satellite HALCA was launched to provide the space-bourne element for the VLBI Space Observatory Program (VSOP) mission. Approximately 25% of the mission time was dedicated to the VSOP survey of bright compact active galactic nuclei (AGNs) at 5 GHz. This paper, the fifth in the series, presents images and models for the remaining 140 sources not included in the third paper in the series, which contained 102 sources. For most sources, the plots of the (u, v) coverage, the visibility amplitude versus (u, v) distance, and the high-resolution image are presented. Model fit parameters to the major radio components are determined, and the brightness temperature of the core component for each source is calculated. The brightness temperature distributions for all of the sources in the VSOP AGN survey are discussed.
59 citations
TL;DR: In this paper, the authors used the Long Baseline Array (LBA) to measure the magnetic field directions so as to distinguish between the two main models of the environment in which methanol masers form: disks or shocks.
Abstract: Aims. We investigate class II methanol masers and the environment in which they form with the Long Baseline Array (LBA). Methods. Using full polarisation VLBI, we were able to measure the magnetic field directions so as to distinguish between the two main models of the environment in which methanol masers form: disks or shocks. Results. We present polarised images of the methanol maser source G339.88-1.26, made with the LBA at 6.7-GHz. With these first polarisation maps made with the LBA, which successfully reproduce observations with the ATCA confirming the new AIPS code, a new technique for Southern VLBI is opened. The magnetic field directions found are inconstant with methanol masers arising in disks for the majority of the emission.
21 citations
TL;DR: In this paper, the authors present relative astrometrically aligned v = 1 and v = 2 J = 1!0 SiO maser maps, at multiple epochs, and discuss the astrophysical results.
Abstract: Oxygen-rich Asymptotic Giant Branch (AGB) stars are intense emitters of SiO and H2O maser lines at 43 (J = 1!0, v = 1 and 2) and 22 GHz, respectively. VLBI observations of the maser emission provide a unique tool to sample the innermost layers of the circumstellar envelopes in AGB stars. Nevertheless, the difficulties in achieving astrometrically aligned v = 1a ndv = 2 SiO maser maps have traditionally prevented a unique interpretation of the observations in terms of the physical underlying conditions, which depend on the nature of the SiO pumping mechanism. We have carried out observations of the SiO and H2O maser emission towards R LMi, using the astrometric capabilities of VERA. Due to the too weak emission of the reference calibrator, we had to develop a special method to accurately relate the coordinates for both transitions. We present relative astrometrically aligned v = 1 and v = 2 J = 1!0 SiO maser maps, at multiple epochs, and discuss the astrophysical results. The incorporation of astrometric information into the maps of SiO masers challenges the weak points in the current theoretical models, which will need further refinements to address the observation results.
12 citations
TL;DR: In this article, the authors present relative astrometrically aligned v=1 and v=2 J=1-0 SiO maser maps, at multiple epochs, and discuss the astrophysical results.
Abstract: Oxygen-rich Asymptotic Giant Branch (AGB) stars are intense emitters of SiO and H$_2$O maser lines at 43 (J=1-0, v=1 and 2) and 22 GHz, respectively. VLBI observations of the maser emission provides a unique tool to sample the innermost layers of the circumstellar envelopes in AGB stars. Nevertheless, the difficulties in achieving astrometrically aligned v=1 and v=2 SiO maser maps have traditionally prevented a unique interpretation of the observations in terms of physical underlying conditions, which depend on the nature of the SiO pumping mechanism.
We have carried out observations of the SiO and H$_2$O maser emission towards RLMi, using the astrometric capabilities of VERA. Due to the too-weak emission of the reference calibrator we had to develop a special method to accurately relate the coordinates for both transitions. We present relative astrometrically aligned v=1 and v=2 J=1-0 SiO maser maps, at multiple epochs, and discuss the astrophysical results. The incorporation of astrometric information into the maps of SiO masers challenges the weak points in the current theoretical models, which will need further refinements to address the observations results.
11 citations
Commonwealth Scientific and Industrial Research Organisation1, University of Calgary2, Swinburne University of Technology3, York University4, Durham University5, University of Sydney6, University of Colorado Boulder7, University of Tasmania8, University of California, Berkeley9, University of Adelaide10, Laval University11, McGill University12, Herzberg Institute of Astrophysics13, California Institute of Technology14, La Trobe University15, University of Toronto16, University of British Columbia17, University of Western Australia18, Curtin University19
TL;DR: The Australian SKA Pathfinder (ASKAP) as discussed by the authors is aimed squarely in this frequency range, and achieves instantaneous wide-area imaging through the development and deployment of phase-array feed systems on parabolic reflectors.
Abstract: [ABRIDGED VERSION] The future of cm and m-wave astronomy lies with the Square Kilometre Array (SKA), a telescope under development by a consortium of 17 countries. The SKA will be 50 times more sensitive than any existing radio facility. A majority of the key science for the SKA will be addressed through large-area imaging of the Universe at frequencies from 300 MHz to a few GHz.
The Australian SKA Pathfinder (ASKAP) is aimed squarely in this frequency range, and achieves instantaneous wide-area imaging through the development and deployment of phase-array feed systems on parabolic reflectors. This large field-of-view makes ASKAP an unprecedented synoptic telescope poised to achieve substantial advances in SKA key science. The central core of ASKAP will be located at the Murchison Radio Observatory in inland Western Australia, one of the most radio-quiet locations on the Earth and one of the sites selected by the international community as a potential location for the SKA.
Following an introductory description of ASKAP, this document contains 7 chapters describing specific science programmes for ASKAP.
The combination of location, technological innovation and scientific program will ensure that ASKAP will be a world-leading radio astronomy facility, closely aligned with the scientific and technical direction of the SKA. A brief summary chapter emphasizes the point, and considers discovery space.
2 citations
04 Mar 2008
TL;DR: In this paper, the authors report the results of simultaneous observations of the Vela pulsar in X-rays and radio from the RXTE satellite and the Mount Pleasant Radio Observatory in Tasmania.
Abstract: We report the results of simultaneous observations of the Vela pulsar in X‐rays and radio from the RXTE satellite and the Mount Pleasant Radio Observatory in Tasmania. We sought correlations between the Vela's X‐ray emission and radio arrival times on a pulse by pulse basis. At a confidence level of 99.8% we have found significantly higher flux density in Vela's main X‐ray peak during radio pulses that arrived early. This excess flux shifts to the ‘trough’ following the 2nd X‐ray peak during radio pulses that arrive later. Our results suggest that the mechanism producing the radio pulses is intimately connected to the mechanism producing X‐rays. Current models using resonant absorption of radio emission in the outer magnetosphere as a cause of the X‐ray emission are explored as a possible explanation for the correlation.