News Article | May 10, 2017
In a milestone for African astronomy, engineers have converted an old telecommunications dish in Ghana into the continent’s first functioning radio telescope outside South Africa. The telescope, in Kuntunse near Accra, is the first of an array of such instruments expected to be built across Africa over the next five years, and forms part of long-term plans to develop the skills of astronomers on the continent. It made its first observations this year and will be formally opened later in 2017. “It’s a moment of pride and joy that we have reached this far,” says project manager T. L. Venkatasubramani (known as VenKAT). He says that science operations should begin next year. Once up and running, the Ghana telescope could be incorporated into the European Very Long Baseline Interferometry (VLBI) Network — a cluster of far-apart radio telescopes that together act as one large instrument. But astronomers also want to use it in a separate African VLBI Network (AVN). For that, plans are under way to convert telecommunications dishes in Zambia, Madagascar and Kenya by mid-2019. The arrival of undersea cables around Africa’s coast in the past decade has rendered these dishes obsolete for their original purpose. New telescopes could also be built in four other African nations by mid-2022. The AVN will develop the capacity for astronomy in countries that have never had a radio telescope, says Huib Jan van Langevelde, director of the Joint Institute for VLBI in Europe, based in Dwingeloo, the Netherlands, who has been involved in training and testing for the African network. But it will also contribute useful science, he notes. The Ghana telescope has begun observing methanol masers — radio emissions that can arise from a number of celestial phenomena — and pulsars. The AVN will fill in geographic gaps in the global VLBI, improving imaging by increasing the range of distances and possible angles between the telescopes in the network. The more telescopes there are in a VLBI network, the more detail astronomers can see. “If you look at the current VLBI network, we definitely do need antennas filling up the centre of Africa,” says James Chibueze, a VLBI scientist and AVN operator who works with SKA South Africa in Cape Town, which is building part of the world’s largest radio telescope, the Square Kilometre Array. Tony Beasley, director of the US National Radio Astronomy Observatory in Charlottesville, Virginia, says the AVN is a “fantastic” initiative for the Southern Hemisphere, where the VLBI at present shares use of an array in Australia. “The AVN would be a full-time array, would do a lot more science and is going to increase by an order of magnitude the amount of VLBI time available, and the southern skies thing is unique. We have lots of arrays in the Northern Hemisphere,” he says. The AVN would also benefit from the technical advances made for the SKA and South Africa’s radio-astronomy ambitions, says Beasley. The AVN was the brain child of Michael Gaylard, a former director of South Africa’s Hartebeeshoek Radio Astronomy Observatory who died in 2014. During two years of repairs to the observatory’s telescope, Gaylard used Google Maps to scour the continent for old telecommunications dishes. When he saw the Kuntunse dish, he realized that it — and others like it — could be converted for astronomy. The switch has been difficult, says Chibueze. New telescopes are designed and built to set specifications, but during work on the Kuntunse dish, engineers and scientists have had to adapt their plans. And there have been issues with the stability of electrical power and Internet supply. The conversion has been in large part funded by South Africa, whose African Renaissance and International Co-Operation Fund and department of science and technology have contributed 122 million rand (US$9 million) to the project. From South Africa’s point of view, the AVN would help to prepare the continent for the SKA: many hundreds of dishes, and even more antennas, are set to be built in Australia and South Africa. By the late 2020s, the SKA project also plans to construct other stations — separate from the AVN — in eight other African nations. Later this year, the AVN project and South Africa’s SKA project office will be amalgamated into the South African Radio Astronomy Observatory, a unit of the National Research Foundation. The plan, however, is that Ghana and other African nations will ultimately own and operate their AVN telescopes. South Africa hasn’t said whether it will fund further conversions. VenKAT says that it needs cost-sharing commitments from other African nations. “We must ensure the governance set-up is in place before we go in for the engineering,” he says. “It’s not just a South African do-and-deliver, but a joint programme.”
Richter L.,SKA South Africa |
Richter L.,Rhodes University |
Kemball A.,University of Illinois at Urbana - Champaign |
Kemball A.,Rhodes University |
Jonas J.,Rhodes University
Monthly Notices of the Royal Astronomical Society | Year: 2016
This paper presents a component-level comparison of the polarized v = 1 J = 1-0, v = 2 J = 1-0 and v = 1 J = 2-1 SiO maser emission towards the supergiant star VY CMa at milliarcsecond-scale, as observed using the Very Long Baseline Array at λ = 7 and 3 mm. An earlier paper considered overall maser morphology and constraints on SiO maser excitation and pumping derived from these data. The goal of the current paper is to use the measured polarization properties of individual co-spatial components detected across multiple transitions to provide constraints on several competing theories for the transport of polarized maser emission. This approach minimizes the significant effects of spatial blending. We present several diagnostic tests designed to distinguish key features of competing theoretical models for maser polarization. The number of coincident features is limited by sensitivity however, particularly in the v = 1 J = 2-1 transition at 86 GHz, and deeper observations are needed. Preliminary conclusions based on the current data provide some support for: (i) spin-independent solutions for linear polarization; (ii) the influence of geometry on the distribution of fractional linear polarization with intensity; and, (iii) π/2 rotations in linear polarization position angle arising from transitions across the Van Vleck angle (sin 2θ = 2/3) between the maser line of sight and magnetic field. There is weaker evidence for several enumerated non-Zeeman explanations for circular polarization. The expected 2:1 ratio in circular polarization between J = 1-0 and J = 2-1 predicted by standard Zeeman theory cannot unfortunately be tested conclusively due to insufficient coincident components. © 2016 The Authors.
News Article | December 16, 2016
The Netherlands and South Africa have set up a data science partnership to establish national and regional data centres in order to tackle one of the most significant challenges presented by the SKA telescope: how to manage, process, and make accessible the immense amount of data the telescope will generate. THE HAGUE, 16-Dec-2016 — /EuropaWire/ — The Square Kilometre Array (SKA) project is a global effort to build the world’s largest radio telescope. It will eventually have a collecting area of over a square kilometre, to be built in South Africa and Australia. The SKA will be used to conduct transformational science, addressing questions on how the first stars and galaxies formed just after the big bang, what the nature of dark energy could be and whether we are alone in the universe. The vast collection area of the SKA will produce staggering amounts of data, requiring key technological innovations in a number of areas such as big data and high-performance computing. The Netherlands and South Africa have set up a data science partnership between key institutions from both countries to address the question of how to deal with these large volumes of data. NWO, ASTRON and IBM have signed a Memorandum of Understanding (MoU) with SKA South Africa and the University of Cape Town to collaborate on a ground-breaking research project entitled Precursor Regional Science Data Centres for the SKA (SKA-RSDC). The MoU provides the vehicle for South African and Dutch partners to collaborate on policies, specifications, test-cases, proofs-of-concept and best-practices that will enable researchers to develop models for the efficient processing and analysis of the large quantity of data, based on the SKA pathfinders LOFAR (Low Frequency Array, NL) and MeerKAT (SA). These models will be an essential step in developing the necessary expertise for the SKA Regional Data Centres. The data centres will provide astronomers around the world with access to the large-scale data infrastructures and associated high-performance computing needed to make sense of the data. The techniques developed can, in turn, then be applied in other fields such as big data analytics, high-performance computing, green computing, and visualisation analytics. Watch the video below for more information on the SKA project. This trailer highlights the scale and ambition of the SKA project, the big questions it aims to answer, and the sheer complexity of the entire undertaking. Last week, the trailer won a European Excellence Award, a distinction that honours outstanding achievements in communication and PR.
Carignan C.,University of Cape Town |
Frank B.S.,University of Cape Town |
Hess K.M.,University of Cape Town |
Lucero D.M.,University of Cape Town |
And 3 more authors.
Astronomical Journal | Year: 2013
H I observations of the Magellanic-type spiral NGC 3109, obtained with the seven dish Karoo Array Telescope (KAT-7), are used to analyze its mass distribution. Our results are compared to those obtained using Very Large Array (VLA) data. KAT-7 is a pathfinder of the Square Kilometer Array precursor MeerKAT, which is under construction. The short baselines and low system temperature of the telescope make it sensitive to large-scale, low surface brightness emission. The new observations with KAT-7 allow the measurement of the rotation curve (RC) of NGC 3109 out to 32′, doubling the angular extent of existing measurements. A total H I mass of 4.6 × 108 M⊙ is derived, 40% more than what is detected by the VLA observations. The observationally motivated pseudo-isothermal dark matter (DM) halo model can reproduce the observed RC very well, but the cosmologically motivated Navarro-Frenk-White DM model gives a much poorer fit to the data. While having a more accurate gas distribution has reduced the discrepancy between the observed RC and the MOdified Newtonian Dynamics (MOND) models, this is done at the expense of having to use unrealistic mass-to-light ratios for the stellar disk and/or very large values for the MOND universal constant a 0. Different distances or H I contents cannot reconcile MOND with the observed kinematics, in view of the small errors on these two quantities. As with many slowly rotating gas-rich galaxies studied recently, the present result for NGC 3109 continues to pose a serious challenge to the MOND theory. © 2013. The American Astronomical Society. All rights reserved.
Merry B.,SKA South Africa
Astronomy and Computing | Year: 2016
Convolutional gridding is a processor-intensive step in interferometric imaging. While it is possible to use graphics processing units (GPUs) to accelerate this operation, existing methods use only a fraction of the available flops. We apply thread coarsening to improve the efficiency of an existing algorithm, and observe performance gains of up to 3.2× for single-polarization gridding and 1.9× for quad-polarization gridding on a GeForce GTX 980, and smaller but still significant gains on a Radeon R9 290X. © 2016 Elsevier B.V.
Merry B.,SKA South Africa
Monthly Notices of the Royal Astronomical Society | Year: 2015
Wprojection is a commonly used approach to allow interferometric imaging to be accelerated by fast Fourier transforms, but it can require a huge amount of storage for convolution kernels. The kernels are not separable, but we show that they can be closely approximated by separable kernels. The error scales with the fourth power of the field of view, and so is small enough to be ignored at mid- to high frequencies. We also show that hybrid imaging algorithms combining Wprojection with either faceting, snapshotting, or Wstacking allow the error to be made arbitrarily small, making the approximation suitable even for high-resolution wide-field instruments. © 2015 The Authors. Published by Oxford University Press.
Sharpe C.,SKA South Africa
Proceedings of the International Astronautical Congress, IAC | Year: 2014
The scope of this paper investigates the socio economic and political issues that enhance and inhibit technological, space and general scientic advancement in African nations. In addition to high-level political factors, within Africa there are unique social, traditional and psychological factors, which come into play at a business and even political level. This paper presents research into the economic, legal and policy issues and benefits relating to space projects and collaboration within the African context, as well as identifying and assessing the major risks and changes underway. In addition, a commentary on the African Union and its strategies moving forward as they relate to space. Socio economic factors can drive, enhance or inhibit development in space, technology and science in African nations. Some important considerations include the level to which technology can be adopted, human capital development capacity, security requirements, available investment and political stability. Equally, political agendas and motivations can grow or stunt technological, space and scientific advancement. Political agends include the pursuit of programmes for national pride, regional dominance and defense, science and academic advancement, development of a private and sustainable commercial industry or the development of national space infrastructure for national social benefit, for example, remote sensing capability and communications. Funding and Sustainability are largely dependent on the motivational push factors. Copyright ©2014 by the International Astronautical Federation. All rights reserved.
Kapp F.,SKA South Africa
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2016
The Square Kilometre Array (SKA) is a large science project planning to commence construction of the world's largest Radio Telescope after 2018. MeerKAT is one of the precursor projects to the SKA, based on the same site that will host the SKA Mid array in the central Karoo area of South Africa. From the perspective of signal processing hardware development, we analyse the challenges that MeerKAT encountered and extrapolate them to SKA in order to prepare the System Engineering and Project Management methods that could contribute to a successful completion of SKA. Using the MeerKAT Digitiser, Correlator/Beamformer and Time and Frequency Reference Systems as an example, we will trace the risk profile and subtle differences in engineering approaches of these systems over time and show the effects of varying levels of System Engineering rigour on the evolution of their risk profiles. It will be shown that the most rigorous application of System Engineering discipline resulted in the most substantial reduction in risk over time. Since the challenges faced by SKA are not limited to that of MeerKAT, we also look into how that translates to a system development where there is substantial complexity in both the created system as well as the creating system. Since the SKA will be designed and constructed by consortia made up from the ten member countries, there are many additional complexities to the organisation creating the system-a challenge the MeerKAT project did not encounter. Factors outside of engineering, for instance procurement models and political interests, also play a more significant role, and add to the project risks of SKA when compared to MeerKAT. © 2016 SPIE.
Schwardt L.C.,SKA South Africa
Proceedings of the 2012 International Conference on Electromagnetics in Advanced Applications, ICEAA'12 | Year: 2012
Compressed sensing (CS) provides the theory behind the CLEAN deconvolution step found in aperture synthesis imaging in radio astronomy and suggests many new algorithms for it. A few CS algorithms, including greedy methods such as Orthogonal Matching Pursuit (OMP) and convex relaxation methods based on Basis Pursuit (BP), are evaluated on a small dataset produced by the KAT-7 array. The new algorithms outperform a standard CLEAN algorithm on this snapshot imaging task. © 2012 IEEE.
Merry B.,SKA South Africa
Parallel Processing Letters | Year: 2015
Sorting and scanning are two fundamental primitives for constructing highly parallel algorithms. A number of libraries now provide implementations of these primitives for GPUs, but there is relatively little information about the performance of these implementations. We benchmark seven libraries for 32-bit integer scan and sort, and sorting 32-bit values by 32-bit integer keys. We show that there is a large variation in performance between the libraries, and that no one library has both optimal performance and portability. © 2015 World Scientific Publishing Company.