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A daily view of all the goings-on at ASTRON and JIVE.

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    © Richard Porcas (MPIfR)

    Note the unusual day and the unusual time: 15:00!

    I will describe the hunt for new quasars made by the Jodrell Bank Survey Group in the 1970's. This involved a new radio survey at 966 MHz made using the recently resurfaced "MKIA" telescope, follow-up accurate position measurements using Jodrell Bank local interferometry and the Green Bank 300ft transit telescope, and optical identifications using the Palomar Sky Survey. Final quasar confirmation followed from optical spectrosopy - with a remarkable discovery.

    The picture above shows the Jodrell MKIA telescope during survey observations in December 1972.

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  • 07/09/14--17:00: Hardware for APERTIF
  • © ASTRON

    During the past two years, lots of hardware has been designed and built for the WSRT/APERTIF project. These images give an impression of some of the control hardware. Even though not every item is worthy of a separate Daily Image, each is essential for the system as a whole, and we have lavished the same love and care on all of them.

    - LO Generator (LOG) Backplane.

    - Down Converter (DCU) Subrack.

    - DCU board.

    - LOG control board.

    - LOG 10 MHz buffer board.

    - LOG Divider and Amplification board.

    - DCU Backplane front.

    - DCU Backplane rear with LO distribution.

    - LOG Signal filtering.

    - LOG Subrack.

    - DCU board including shielding cans.

    - DCU and DCU control backplanes.

    - Complete testset for DCU board.

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    © Erwin de Blok

    The picture shows WSRT observations of the neutral hydrogen gas in galaxy NGC 4414, overlaid on a background optical image. NGC 4414 was observed as part of the HALOGAS survey. This deep survey of nearby galaxies aims to help solve the riddle of where the gas in galaxies comes from. Galaxies do not have enough gas to sustain their current rate of star formation and must be resupplied from somewhere.

    The HALOGAS observations showed that the optically very normal looking galaxy actually has an extended and disturbed neutral hydrogen disk, as shown the picture. This distribution can be modelled as a so-called "U-shaped warp" - what we are seeing is that the outer, low-density parts of the disk get pushed and slowed down by the intra-galactic medium as the galaxy moves through space, resulting in the disk looking like a dinner plate. These new, deep observations of NGC 4414 presented here show that even apparently undisturbed galaxies are interacting with their environment. For more information see

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  • 07/13/14--17:00: Best paper award at ISC 2014

    The International Supercomputing Conference (ICS) is Europe's biggest conference in the field of High Performance Computing. Over 2500 attendees from academia and industry traveled to Leipzig, Germany, to listen to interesting talks and make business.

    This year, a team of DOME researchers from the Accelerators work-package took home the 'Gauss' best paper award, sponsored by the German Gauss Centre for Supercomputing. The awarded paper, Exascale radio astronomy: can we ride the technology wave?, discusses the feasibility of realizing the SKA with commercial off-the-shelf technology. It is authored by Erik Vermij (IBM Research), Leandro Fiorin (IBM Research), Christoph Hagleitner (IBM Research) and Koen Bertels (TU Delft).

    The paper concludes that novel system designs as well as novel node/device designs are necessary to reach the performance and power efficiency goals off the SKA project. This is also a justification of the DOME project: in order to make the SKA a success, a significant research effort is needed.

    The research paper track is only a small portion of this big conference. Other topics range from the Top 500 release (fastest supercomputers in the world) to very technical discussions about novel programming models (OpenMP 4.0, PGAS), and from real-life HPC applications (healthcare, oil and gas) to new product releases. Another key element of the conference is the large number of forums, where the brightest people from research and industry engage in an open discussion with the audience about hot topics in the field.

    The picture shows the award ceremony. From left to right: Claus Axel Muller (GCS managing director), Koen Bertels, Leandro Fiorin, Erik Vermij, and Michael M. Resch (GCS chairman).

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  • 07/14/14--17:00: ASTRON Bike To Work Day 2014
  • © JvL

    On Monday June 16, a group of ASTRON-ners that live farther away left their cars and train cards at home, to bike to ASTRON. In the image above you can see the stylized tracks, overlaid on the road-race cycling heat map of The Netherlands. Starting first in Utrecht at the year's earliest sunrise (05:18), then picking up people, or forming own groups, in Amersfoort, Zwolle, Meppel, Assen en Groningen, we arrived at ASTRON right on time for coffee. Join us next year to celebrate these longest days of the year to get active!

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    © Jean-Pierre Macquart

    On Monday 7 July the Dutch Ambassador to Australia, Mrs Annemieke Ruigrok, paid an impromptu visit to ICRAR/Curtin University, Perth. The Ambassador was accompanied by Mr Rolf Karst, Trade Officer, Economic Affairs. Her Excellency was keen to hear about recent progress by the Aperture Array Design and Construction (AADC) Consortium and, as part of the briefing and discussion, the gathering toasted the success of ASTRON and its university partners in successfully obtaining Dutch Government support for SKA pre-construction activities, including the development of the Low Frequency Aperture Array.

    Professor Peter Hall told Her Excellency of the success of the AADC Consortium establishment, and the design work now being undertaken. She was also briefed by task leaders on the prototyping, verification and infrastructure work being done at Curtin, as well as on developments in the SKA science prioritization process.

    In the photograph from left to right: Mr Rolf Karst, Prof. Steven Tingay, Her Excellency the Ambassador, Professor Carole Jackson and Prof. Peter Hall.

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    © Astron

    Recently, four UniBoards have been installed in Westerbork for APERTIF. These UniBoards are configured as correlators and are able to correlate 28 beams over the full 300 MHz bandwidth of 3 WSRT dishes. The correlator image for the UniBoard is called the Quick and Dirty Correlator (QDR). It was realized in only half a year thanks to the extensive usage of reusable blocks from the Astron firmware library. This FPGA-based correlator handles a data input rate of 480 Gbit/s which is the highest input rate for a correlator ever built by Astron. Note that the final Apertif correlator will be able to handle 8 times more data: 3.8 Tbit/s (see daily image 31-5-2015).

    The QDR Correlator finds its limitations in the maximum number of inputs (= 3) and the fact that it processes 781 kHz subbands instead of 10kHz channels. It will be used for the commissioning of Apertif Alpha III.

    The picture shows the correlator with its 48 fibres. The fibres originate at the WSRT dishes and carry the beamlets that are produced by the

    beamformer racks. The correlator is placed inside the HF-cabine in the main building at the WSRT.

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    © JIVE, Arnold van Ardenne

    On 15 July 2014 a South African delegation visited Astron and JIVE. The goal of this visit was to strengthen partnership between South Africa and The Netherlands in astronomy in general, and in dealing with the transport, processing and archiving of huge amounts of data in particular. This is very important for future radio facilities like the Square Kilometre Array (SKA) and the African VLBI Network (AVN).

    The South African delegation consisted of Dr. Thomas Auf der Heyde (Deputy Director-General: Research Development and Support, Department of Science and Technology), Mr. Takalani Nemaungani (Director: SKA and AVN, Department of Science and Technology), Mr. Isaac Maredi (Chief Director: Sector Innovation and Green Economy, Department of Science and Technology), Dr. Patrick Woudt (Astronomer: University of Cape Town), Dr. Jasper Horrel (General Manager: Science Computing and Innovation, SKA South Africa), Dr. Anwar Vahed (Principal Scientist: Meraka Institute, CSIR) and Prof. Colin Wright (Manager: Cyber Infrastructure Unit, Meraka Institute, CSIR).

    They are accompanied by Dr. Louis B.J. Vertegaal (Director: Physical Sciences, NWO), Dr. Ronald Stark (Head of Astronomy, NWO), Prof. Huib van Langevelde (Director: JIVE) and other JIVE staff members (Bert, Bob, Mark and Zsolt).

    The discussions at JIVE focused on the South-African participation in JIVE, and the joint interest to develop VLBI in Africa, the MeerKAT radio telescope, the verification of aperture arrays, and of course SKA.

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    © N. Werner (Stanford University)

    A study led by N. Werner (Stanford University) and J.B.R. Oonk (ASTRON) discovered for the first time the cold gas component of the filamentary H-alpha web surrounding M87. These gas webs surrounding the cD galaxy are common in cool-core clusters. The cool H-alpha gas is so luminous that it requires constant reheating by a still unknown source (i.e. part of the cooling flow problem).

    In order to determine the origin and excitation of these filaments we need to understand their local mass and energy budget. M87 is the nearest cool-core cluster and therefore important. Attempts at characterizing its filamentary web have been difficult as the low temperature phase of this gas (HI, CO) is not detected. This is primarily due to the strong continuum source affecting the spectral baseline.

    Now, with Herschel, we have succeeded in detecting and spatially resolving the [CII] (157 micron) emission along the south-eastern filaments. The upperlimit on the [OI] to [CII] FIR line ratio indicates a large optical depth in the FIR lines. In combination with the absorption inferred from optical lines and X-rays this indicates the presence of a significant reservoir of cold atomic and molecular gas distributed in filaments with small volume filling fraction, but large area covering factor. We find good correspondence, in both intensity and kinematics, between the cool (T~1e4 K) and cold (T~100 K) gas.

    A multi-wavelength study shows that the cool gas (T

    Figure caption: The multi-phase structure of the South-eastern filaments surrounding M87. The top panels show the Far-infrared CII-157 micron structure of the cold (100 K) gas in intensity and dynamics. The middle panels show the corresponding optical H-alpha, Far-ultraviolet and X-ray emission. The bottom panels show the emission measure of the hot X-ray emiting gas at three different temperatures from cool (left) to very hot (right).

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    © ASTRON

    The days of the lone astronomer with his optical telescope and photographic plates are long gone. The future of astronomy will not only be multi-wavelength, but multi-messenger in nature, often dominated by huge data sets and matching data rates. Catalogues listing detailed properties of billions of objects will in themselves require a new "industrial-scale" approach to scientific discovery, requiring the latest techniques of Advanced Big Data Analytics to be applied. An early engagement with the first generation of cognitive computing systems is also a looming opportunity for our field.

    Projects like the ASTRON-IBM DOME collaboration are important vehicles for making early progress in these exciting new areas of multi-disciplinary research. Applying cognitive computing to large astronomical surveys, could have a huge impact in terms of serendipitous discovery - areas that might especially benefit include those like SETI, where human bias and other pre-conceptions may limit current efforts.

    The image above shows IBM�s Watson machine (left) and a LOFAR based SETI search campaign (right). Watson represents an important step forward towards realising cognitive computer systems but further progress requires revolutionary new architectures to be developed that mimic the human brain.

    A paper describing these opportunities was presented at the recent Radio 2014 meeting:

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    © astron

    On June 5th, we had the third get-together of the PhD students that are supervised by the astronomers at ASTRON. Thanks to the various personal grants (like ERC) and the collaboration with NOVA, we now have a record number of PhD students. They visit ASTRON regularly but they spend most of their time at their university, in particular Groningen and Amsterdam.

    The get-together aimed at offering the opportunity to the students to present their projects, and to the ASTRON astronomers to present some of the work done in the astronomy group. We had a full program, with long presentations from those who are already advanced in their PhD, and short presentations from the others.

    The projects of the students cover a broad variety of science and technical topics and are making use of all our facilities, from the WSRT to LOFAR. Some of them are aimed at preparing for the upcoming Apertif. The get-together would of course not have been complete without a lunch at the BosPub, and the final "borrel".

    With more students starting soon, we plan to regularly organize events like this. This will give the opportunity to everybody (students and astronomers) to stay uptodate on the progress of all these extremely exciting projects.

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    © A.shulevski, R.Morganti, N.Vilchez

    This image(*) of a LOFAR HBA observation centrered on J1441+1331 was generated by the Standalone Selfcal Tool (SST) that is part of the LOFAR imaging pipeline. It is one of those tools that does not presume to reach the noise, but achieves a considerable improvement, efficiently and robustly.

    Self-calibration solves for instrumental errors by comparing the observed data with values that are predicted by a model of the observed field. It is an iterative process, in which the sky model is updated in each cycle, until some convergence criterion is met. In addition, the SST also determines what is the best resolution available in the data, and it will start at 15 times the estimated value. At each cycle (the number of cycles is an input parameter defined by the user), the resolution is improved and finally converges, cycle by cycle, to the best resolution.

    Each cycle contains 3 steps:

  • A phase calibration step using the sky model extracted at the previous cycle

  • an imaging step

  • a source extraction step to create a new sky model which will be used at the next cycle.

    The SST generally improves the image quality by a factor 6 to 10. The final noise is typically 5-6 times the thermal noise.

    For this image, we used the SST on 14 groups of 20 subbands each. The resulting 14 images were then combined into one continuum image with a total bandwidth of 280 HBA subbands, or 56 MHz (115 MHz to 171 MHz). The final spatial resolution is 5 arcsec. The final noise is 0.5mJy while the thermal noise (confusing noise) is 0.2 mJy. The target object (J1441+1331) is at the center of the image, and the FOV is 4�x1.6�.

    In future improvements, we plan to implement directional phase calibration, and to take taking account of ionospheric effects, especially for long baselines.

    (*) An entry into the recent ASTRON astronomical poster competition that was held to select impressive wall decorations for the new astronomy wing.

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  • 07/24/14--17:00: ASTRON/JIVE MTB 2014
  • © JvL/EK

    On Wednesday June 18 the annual ASTRON/JIVE MTB afternoon celebrated its fifth anniversary, and thus featured a special program: a talk and clinic by the first Olympic Champion MTB, Bart Brentjens(*). For a packed Hooghoudt room Bart, currently a team manager, gave a short presentation on the factors that are important for success in sports -- Talent, Technique & Teamwork. Bart explained how professional mountain bikers live and train. He brought his own bike and explained the technical innovation process. Finally he outlined how a team of cyclists functions and how it is supported to reach the best possible results. At the end Bart responded to a range of questions.

    After that, three groups of about 12 cyclists, ranging from daily cyclists to experienced mountain bikers, got onto their wheels. Bart first explained bike setup, then moved to a demonstration field (with props and hill) next to the ASTRON building. There he explained e.g., where to put your weight in corners/climbs/descents. After that, groups took a special 3-km loop throughout the forest that included a nicely steep sandy hill, many other training obstacles, and a very scenic setup with the Dwingeloo telescope in the background. The afternoon was concluded with a few healthy snacks and refreshments (**), and the opportunity to ask any last questions.

    A great afternoon again -- thanks Eric, Alex and Marja for helping to organize; and to all who came out for making it such a success!

    (*) Bart is a full cousin of our very own Michiel Brentjens. A talented family, obviously.

    (**) Including no less than 6 cans of beer.

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  • 07/27/14--17:00: LED it be - 3D prototyping
  • © foto: Wim van Cappellen / Ronald Halfwerk

    Again, ASTRON's 3D printer proved to be very useful for making complex 3D geometrical shapes available during the design phase of an instrument. Tom Raasveld, a graduate student from Hanze Hogeschool Groningen used it for designing a new LED ring for a contactless measuring machine.

    Shining more light on a measured object reduces the exposure time, and thus accelerates the measurement process. One of the design goals was to have the intensity of the light evenly distributed over the field of view of the camera. Tom made the calculations for approx. 100 green Light Emitting Diodes (LEDs). The latter had to be grouped around the optics in a ring shape, preferably tilted slightly towards the object.

    The measuring machine saw "first light" at the Holland High Tech pavilion in Hannover, April 2014. Branded as YIM3D by ASTRON spin-off company DutchSigma BV, it is bound to have a bright future.

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    © David Kaplan et al.

    " a diamond in the sky". If you believe your nursery rhymes, then stars should twinkle like diamonds in the sky. Reality, however, has shown us quite the opposite: it is the absence of a visible star in this optical image that leads us to conclude that we found a diamond in the sky. Making this connection, however, required a big stack of data from a wide range of astronomical facilities.

    The point marked in the optical images is the location of the radio pulsar J2222-0137, discovered by the Green Bank Telescope in 2007. The pulsar is in a binary system, orbiting its companion every 2.45 days. Timing the arrival of the radio pulses can measure many orbital properties, including the fact that it is very circular, and the General Relativistic "Shapiro" delay which shows that its companion is slightly more massive than our Sun. The circular orbit makes it almost certain that the pulsar's companion is a white dwarf - the violent explosion necessary to form a second neutron star would have perturbed the system into an eccentric orbit.

    White dwarf stars are generally faint, but not invisible - and so we fully expected to see the companion when taking optical observations with the Keck and SOAR telescopes. However, as the figure above shows, nothing can be seen at the position of the pulsar! Astrometric measurements with the Very Long Baseline Array (see here) had already pinned down the distance to the system to better than 1%, so the dimness is not a result of the star being very distant. The only remaining explanation is that the system is nearly as old as the Milky Way galaxy, and the white dwarf is now very, very cold. So cold, in fact, that the carbon which makes up the bulk of the white dwarf would have crystallised and formed a colossal diamond - possibly 1000 times heavier than the famous diamond planet!

    These results were recently reported in the Astrophysical Journal (Kaplan et al., 2014, 789, 119). In the near future, approved observations with the Hubble Space Telescope should finally get a glimpse of the biggest diamond known in the sky.

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    © Vibor Jelic

    The presence of polarized foregrounds is a serious complication for epoch of reionization (EoR) experiments. To avoid the leakage of polarized emission into total intensity, which can depend on frequency, we need to calibrate the instrumental polarization across the field of view to a small fraction of 1%. Given the rather uniform levels of the polarized intensity, the polarity of Stokes Q,U is a good indicator of the spatial variations of the plane of polarization.

    The figure shows LOFAR HBA (150 MHz) wide-field images of polarized emission from our Galaxy (the ELIAS-N1 region) in:

  • polarized intensity (PI, first column)

  • Stokes Q (second column)

  • Stokes U (third column).

    The RM-synthesis images are given at Faraday depths of -1.5, -0.5, +0.5, and +1.5 rad/m2 (different rows). They are 5.7deg x 5.7deg in size with a resolution (PSF) of 3.4 arcmin x 3.1 arcmin. The fractional polarization at 150 MHz, expressed as a percentage of the total intensity, amounts to 1.5%. There is no indication of diffuse emission in total intensity in the interferometric data, in line with results at higher frequencies. The average brightness temperature of the detected emission is 4 K. This is much more than was anticipated on the basis of earlier observations with other telescopes.

    For comparison, we have also used the WSRT at 350 MHz to image the same region. The LOFAR and WSRT images show a similar complex morphology at comparable brightness levels, but their spatial correlation is very low. The different polarized patterns observed at 150 MHz and 350 MHz are consistent with different source distributions along the line of sight wring in a variety of Faraday thin regions of emission.

    The wide range and richness of the detected morphological features demonstrate once more the power of low frequency polarimetry with LOFAR for studying the interstellar medium at high Galactic latitudes. Its wide frequency range, high angular resolution, and high sensitivity make LOFAR an exquisite instrument for studying Galactic polarized emission at a resolution of 1-2 rad m^-2 in Faraday depth.

    For more details:

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    About a year ago, a small group of expert developers was assembled in order to update the capability of the LOFAR Standard Imaging Pipeline (SIP), which is used to automatically form images from interferometric data immediately after observations. This group is referred to as a "Tiger Team," reflecting the fact that it is highly focused on achieving a specific goal - enabling the production of high quality science-ready images in an automatic fashion. The CITT is made up of eight members and is supported by an expert Advisory Group that provides input and feedback, and a team of community testers that help to verify the software enhancements.

    During the first year of CITT activity, the team has demonstrated marked improvements to calibration and imaging routines, as well as providing a functional and widely-used self-calibration script. It has also made important progress toward the realization of an automated direction-dependent calibration scheme. Drawing all of these development threads together into an enhanced pipeline is the central goal of the coming year of work for the CITT.

    In order to reflect on the past year of progress, and plan for the future, the CITT recently held a full-day workshop at ASTRON. The Advisory Group and expert community testers were invited to attend and bring their unique expertise to the discussions. Many of the workshop attendees are shown in today's image, casually hanging out together at a coffee break. The workshop itself was very successful and has helped to clarify the activities needed to realize the ambitious goal of a newly capable pipeline. We look forward to still more progress in the second year of Tiger Team activity!

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    © Authors/Noordam

    To celebrate and decorate their revamped wing of the building, the Astronomy Group recently organized the "Astronomy Pretty Poster Pageant (APPP) 2014", for catchy, visual, and colorful posters based on an astronomical image. The best of the 46 (!) submitted posters will be placed around the AG corridors, with a large attractive display for the winning poster, as determined by an eminent judging committee.

    The winners of the event, shown above, were:

  • (1st) Tom Oosterloo, "M101", a new, sharp, colorful image from the last deep observation of the pre-Apertif WSRT

  • (2nd) John McKean, "Global VLBI imaging of the gravitational lens MG J0751+2716", a strikingly simple picture of one of the most intriguing effects of gravity

  • (3rd) Charlotte Sobey, "PSR B0823+26: Emission modes in single pulses", a stark visualization of very new LOFAR data with a nod to 70s punk.

    Congratulations to all three!

    All entries that are not embargoed and weren't recently submitted will be run as a ASTRON/JIVE daily image -- enjoy! High-resolution posters are also available for download, for all ASTRON outreach, PR, presentation and other uses. Ask or Joeri.

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    © NOVA Optical Infrared Instrumentation group at ASTRON

    The NOVA Optical Infrared instrumentation group at ASTRON is responsible for the two Cold Optics Benches (COB) of MATISSE. Last week the N-band COB was delivered to Observatoire de la Cote d'Azur in Nice (France). This milestone marks the start of the full integration and overall test of MATISSE.

    MATISSE is an instrument that is designed to coherently combine the light from up to four optical telescopes of ESO's Very Large Telescope Interferometer (VLTI) in Chile. It operates in the in the 2.8-5 and 8-13 micrometer wavelength bands, at spectral resolutions between 30 and 5000. MATISSE is extremely well-suited for the study of Young Stellar Objects (YSOs), extra-solar planets and Active galactic nuclei (AGNs), asymptotic giant branch stars (AGBs) and planetary nebulae.

    In Nice, the COB was unpacked and the transport verification was carried out. We can conclude that all went very well and that the COB is in excellent shape. Mechanisms, wiring and sensors were verified on proper functioning, images were taken with the technical camera, and no evidence of misalignment in the optics was found. The integration team continued with mounting the COB into the cryostat, after which the instrument was moved from the assembly hall towards the MATISSE lab. This delicate operation was also successful.

    The picture shows the cryostat just after it arrived in its transport lorry at its location in front of the Warm Optics Bench. From left to right: Pierre Antonelli (OCA), Marcus Mellein (MPIA), Sylvie Robbe-Dubois (OCA) and Felix Bettonvil (NOVA).

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    © Iniyan Natarajan

    Since May, four members of the Radio Astronomy Techniques and Technologies group(*) of Rhodes University (South Africa) have been based at ASTRON(**), working on various projects related to calibration, modeling, and simulation.

    • Dr Trienko Grobler (Rhodes, SKA-SA) has developed the mathematical framework to describe the infamous 'ghost' sources in WSRT images.

    • Sphesihle Makhathini (Rhodes) has developed a number of simulations which are being used to help define the SKA1-mid antenna layout.

    • Iniyan Natarajan (UCT) is working on a Bayesian approach to interferometric calibration, and involved with the development of the generalized aw-imager

    • Dr Griffin Foster (Rhodes, SKA-SA) has been working to develop a polarization calibration method for low-frequency elements such as the LBA, HBA, and PAPER dipoles.

    Today, three of them will offer brief presentations about their work at a special edition of the TechnoLunch (12:30, Hooghoudt Room).

    Photo: On a brief trip to the LOFAR superterp Griffin, Trienko, and Iniyan (left to right) discuss the anomalous radio source Sphe-A (top left). This exchange has been part of the MIDPREP collaboration between South Africa, ASTRON, and Chalmers University (Sweden).

    (*) The Centre for Radio Astronomy Techniques and Technologies (RATT) is based around the SKA Research Chair of prof Oleg Smirnov (Rhodes University, South Africa).

    (**) Distance makes the heart grow fonder. Both sides greatly value the special relationship.

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