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

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    © ASTRON

    Did you know there's an OpenCore in LOFAR? And another one in APERTIF?

    Our radio telescopes (and other cool things) are built with FPGAs (Field Programmable Gate Array) at their hearts. All FPGA geeks know OpenCores; an online collection of Free and Open Source code ('cores') for FPGA applications. It's where electrical engineering students try to find a shortcut for their assignments. It's also where professionals go to prevent reinventing the wheel (for example, there are over 150 CPU implementations on OpenCores).

    With its big core collection and its very large (specialized) user base, OpenCores has a lot of potential. Andrea Borga from Nikhef (on the right in the picture) recognized this and started up Oliscience (Open Logic Interconnects Science), which then took over the OpenCores website.

    On 14 June, Gert Kruithof (head of ASTRON R&D) put his signature on a partnership agreement (adapted by Ronald Halfwerk, our Technology Transfer Officer) between ASTRON and Oliscience, stimulating OpenCores to grow into a platform that speeds up the development of FPGA based science applications. Following Nikhef, ASTRON is the second institute to jump on board, and most likely more institutes will follow.

    We are already known for our FPGA-based High Performance Computing boards (UniBoard2, Gemini) that can be reconfigured for different applications. Via our Technology Transfer Office we're always on the lookout for new application domains that can benefit from our hardware and the collection of firmware cores we've designed over the years. OpenCores allows us to showcase these cores such that developers worldwide can find and use them in their own applications.

    'Did you know there's an ASTRON core in there?'

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    © R. Schulz

    An active galactic nucleus (AGN) releases a vast amount of energy that affects the evolution of its host galaxy through a complex interplay between accretion of matter onto the central supermassive black hole, gas from the interstellar medium (ISM) and star formation activity. In particular, the AGN can cause outflows of ISM gas which could prevent accretion and star formation. In this recently accepted paper, we focus on one aspect of this interaction which is well suited for high-resolution radio observation: the interaction between radio jets and neutral atomic hydrogen gas.

    To this purpose, we study the active galaxy 3C 236 which is not only one of the largest known, but shows also signs of recurring AGN activity. The inner 1kpc-region is dominated by a (young) compact steep spectrum radio source, towards which previous WSRT observations revealed a high-velocity and massive outflow of hydrogen gas in absorption. In our new paper, we investigate the outflow in detail with a global very long baseline interferometry (VLBI) array comprising the European VLBI Network (EVN), Very Long Baseline Array (VLBA) and the Arecibo radio telescope which is complemented by a Very Large Array (VLA) observation. The VLA data confirms the presence of the outflow and the excellent high-resolution of our VLBI observation allows us to spatially resolve the outflow. Even though we do not manage to recover all of the outflow seen by the WSRT and VLA, we detect four distinct clouds that have kinematic properties inconsistent with the regular rotation of the majority of the hydrogen gas. The highest velocity cloud reaches a velocity of more than 600km/s. It is possible that "missing" outflow consist of clouds similar to the ones that we detected, but we cannot rule out the presence of a diffuse outflow component.

    The image shows several 3D renderings of the hydrogen gas in front of the radio continuum source that we observe with VLBI. The entire animation which also features a great LOFAR image provided by Aleksander Shulevski (paper in preparation) was done with Blender and is available on YouTube:

    Reference: R. Schulz, R. Morganti, K. Nyland, Z. Paragi, E. K. Mahony,

    T. Oosterloo, A&A accepted,"

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    © Colloquium

    Pulsars and their synchrotron nebulae have been extensively observed in the gamma-ray energy band for the last 15 years. The data taken with the Fermi satellite increased the number of known gamma-ray emitting pulsars by one order of magnitude, being currently about 200. On the other hand, the imaging Cherenkov telescopes proved that pulsar wind nebulae are the most common class of sources radiating in the very high energy (VHE; >100 GeV) sky. For the first time population studies are within the reach providing an unprecedented opportunity to test the pulsed and nebular emission models on the market. This vast variety of high-precision spectral and morphological measurements along with the computing technical advances that allowed for deep CPU-consuming simulations led to a significant progress in the understanding of the radiation and particle acceleration mechanisms at work. In this contribution, I will review the latest, and most significant experimental gamma-ray results that led to the construction of a new view of the pulsar magnetosphere and its surroundings. In addition, I will summarize the perspectives in this field for the future gamma-ray instruments, mainly the Cherenkov Telescope Array.

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    © ASTRON

    A short while ago I was invited to celebrate the 25th anniversary of the Leidsch Astronomisch Dispuut `F. Kaiser' that I started with some fellow students in 1993. Being there, in the beautifully renovated old Leiden Observatory, I was reminded again of the remarkable Dutch astronomers that laid the basis for our current high quality of astronomical science. Here at ASTRON, for instance, we are all familiar with famous Dutch astronomers J.H. Oort and H. van der Hulst, who stood at the birth of Dutch radio astronomy and thus of ASTRON.

    But there were others as well. One of them is not well known, but certainly has gained the right to stand in the gallery of Dutch astronomy legends. That person is Frederik Kaiser (1808-1872). He is the namesake of the Dispuut we founded 25 years ago, and for a good reason.

    Kaiser, when only 18 years old, was hired as "Observator" at the Leiden Observatory. He made quite an impression by his precise work and his early publications, among which a famous paper on the orbit of Halley's comet in 1835. Soon, he was promoted to both, Lector in Astronomy and Director of Leiden Observatory. This was in 1837, when Kaiser was only 29 years old. His life mission: lift Leiden Observatory to a standard where it could compete internationally. In 1837, the Observatory was still situated on the top floor of the Academy building in Leiden (a former monastery, see picture), which was definitely not a great place for accurate telescopes. He started out with some structural improvements, but soon found out that he had reached the limits of what was achievable in that location. Kaiser's main interest was in the accurate measurements of stellar positions, and for that a very stable environment is vital.

    Thanks to a successful political lobby, he was finally able to secure adequate funding to build a whole new Observatory on a piece of the botanical gardens in Leiden. This new building was finished in 1860, and was completed with several new instruments for accurate stellar position measurement. Kaiser, in the meantime, excelled in developing methods to properly account for observational errors in his position measurements, and was able to produce the most accurate positions of that day. This achievement and his talent were internationally widely recognized and Kaiser was therefore the first internationally renowned Dutch astronomer. Many of his colleagues visited him in Leiden, to learn his accurate methods for observing stellar positions.

    After his death in 1872, Leiden Observatory continued playing a very visible role in international astronomy. As such, Kaiser laid the foundation for Dutch astronomy, a foundation solid enough to enable famous successors, such as De Sitter and later Oort, to flourish. The building itself was beautifully renovated a few years ago (see picture) and still houses several of the original instruments in working order; others can be found in museum Boerhaave in Leiden, which certainly deserves a visit as well.

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    © ASTRON

    The third PhD student of the ERC RadioLife project, Francesco Santoro, has successfully defended his PhD thesis on Friday June 1st at the University of Groningen.

    Already from the title, "The multi-phase ISM of radio galaxies: a spectroscopic study of ionized and warm gas" one can see that the thesis of Francesco was somewhat special inside the RadioLife project: instead of radio data, it used optical and infrared observations.

    The reason for this is that these data provide key information to characterise galaxies hosting the radio sources. They tell us about the stellar population and its history, the mass of the central black hole, the physical conditions and the motion of the warm gas, and how his gas may be affected by the shocks produced by the radio jet. All this enriches and complement the information obtained from the radio.

    Francesco has used data obtained with some of the best instruments available at the ESO-VLT: MUSE, Sinfoni and X-shooter and combined them with available radio data. To do this, he has learned about the intricacies of the data reductions and pipelines of all these instruments building up a very solid expertise.

    This has paid off and he can now continue his career at the MPI in Heidelberg, working at a project using his favourite instrument: the Multi Unit Spectroscopic Explorer (MUSE)!

    The pdf of his thesis can be found here, but if you would like a proper paper copy, please ask!

    Congratulations Francesco, good luck with your new position and keep up with exciting work with the ESO instruments!

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  • 07/09/18--17:00: LOFAR 2.0 Busy weeks
  • © ASTRON, 2018.

    LOFAR 2.0 delivers a series of expansions and upgrades making the International LOFAR telescope the world's most powerful very-low-frequency, and long-baseline, radio interferometer until at least 2030. The first stage of upgrades include simultaneous LBA and HBA observing, a central clock, new calibration pipelines for the LBA, and the first steps towards an improved robustness against RFI, including windmills.

    A successful delivery of these upgrades requires a thorough preparation: Which science is being addressed? What capabilities should the telescope provide? How do we operate the telescope? Which future expansions are foreseen? What are the boundary conditions such as RFI, capital and operational costs, maintainability?

    In a series of busy weeks, we are laying the foundation for these upgrades by answering the above questions. The result will be a set of system engineering documents defining the use-cases, operational concepts, science requirements, system requirements and the system architecture.

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    © LOFAR MSSS team

    For the past three months, Christiaan Bozon, a bachelor's student at the University of Amsterdam, has been working with Joe Callingham and Jess Broderick on finding peaked-spectrum sources in the LOFAR Multifrequency Snapshot Sky Survey (MSSS).

    Peaked-spectrum sources are postulated to be the young, compact precursors of larger-scale radio galaxies. MSSS has the potential to be particularly advantageous in identifying peaked-spectrum sources: rich spectral information is provided by eight, 2-MHz bands over the frequency range 119-158 MHz.

    First, a number of quality control tests were performed, with a particular focus on the flux density scale of MSSS. Then, using 10 per cent of the survey area (about 2300 square degrees), a pilot sample of 234 peaked-spectrum sources was selected by developing a series of selection criteria.

    The radio spectrum shown above is one such example. The data points are as follows: 74 MHz (VLSSr; purple), 119-158 MHz (MSSS; red), 147 MHz (TGSS; light blue), 325 MHz (WENSS; green), and 1400 MHz (NVSS; dark blue). The two orange lines are separate single-power-law fits to (i) all of the MSSS data, and (ii) the top two MSSS frequency bands as well as NVSS. The black line is a fit to all data points; the turnover frequency is at 265 MHz.

    Studies of large samples of peaked-spectrum sources will help us develop a better understanding of the absorption mechanisms resulting in spectral turnover, which will in turn lead to a more refined view of the evolution of active galactic nuclei.

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    © Bruno van Wayenburg

    A light cannon ball hits the ground at the same time as a heavy cannon ball when dropped off the leaning tower of Pisa. Even the Earth and the Moon fall in the same way towards the Sun. Einstein�s theory of gravity, general relativity, predicts that all objects fall in the same way, regardless of their mass or composition.

    But most alternative theories predict that objects with extreme gravity, like neutron stars, fall a little differently than weak gravity objects.

    That�s why our astronomers Anne Archibald and Jason Hessels have used a natural laboratory to test this theory in extreme conditions: the triple star system called PSR J0337+1715, consisting of a neutron star and two white dwarfs.

    Their findings, published in Nature on 5 July 2018, prove that Einstein�s theory still passes the test in such extreme conditions.

    You can find the full press release about this science story here.

    We have been working together with science animator Bruno van Wayenburg to produce a really nice animation video about this Nature publication for the general audience.

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  • 07/12/18--17:00: Hier... Radio-Melkweg!
  • © Stichting IVIO

    Before the advent of internet, people had to learn about the world by reading books. In the 1930s, a Dutch initiative started publishing booklets on a weekly basis about "Algemene Onderwerpen" (general topics). This became known as the AO-series. The series is still running (now on a monthly basis), the current edition is 3051.

    In the week of the opening of the Dwingeloo Telescope, the topic of edition 605 in the AO-series was radio astronomy. The text, a nice introduction to radio astronomy, was written by dr. J. Houtgast, secretary of Stichting Radiostraling van Zon en Melkweg in 1956.

    To appreciate the broad scope of the AO periodical, note that the surrounding editions were about "Easter Island" (604) and "Diseases from insects" (603).

    I found one of these booklets online (it's actually A5-sized) and will deposit it in Astron's library. The booklet can apparently still be ordered.

    I invite readers of the daily image to complete the crossword on the cover, which includes radio astronomical terms. Please note however that the submission deadline has passed by about 62 years.

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    © Anne Archibald

    We carried out a test of Einstein's theory of gravity with the millisecond pulsar in a stellar triple system. We showed that the pulsar and its inner white dwarf companion experience accelerations that differ by no more than three parts in a million. This is a summary of the Nature paper. There's also a nice News and Views article by Clifford Will.

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  • 07/16/18--17:00: Scaling SAGECal to SKA
  • © Hanno Spreeuw

    SAGECal [1, 2] has been designed to meet not only the challenges of calibrating present-day radio telescopes like LOFAR, but also to handle the data rates of telescopes under construction, like Square Kilometre Array (SKA). To validate this, we have developed new GPU accelerated code and measured the times Sagecal needs to predict the sky and beam for five artificial data sets, having 64, 128, 256, 384 and 512 stations and for five numbers of sources. The size of these datasets obviously increases with the square of the number of stations (N) since the number of baselines equals 0.5xN(N-1). In this figure we depict sky plus beam prediction times for both the CPU as well as the GPU version of Sagecal. For this research, we have used a cluster node equipped with two CPUs (2x Xeon E5-2660v3, 40 logical cores) and a Titan-X (Pascal) GPU on ASTRON's DAS5.

    Both versions depend quadratically on the number of stations, but the GPU version is about ten times faster. In this research, we have explored GPU utilisation and latencies to improve Sagecal performance. We have reduced latencies in the two most important kernels. Our future work involves optimization of a number of other kernels within Sagecal, including the kernels that do the actual calibration.


    [1] S. Yatawatta, S. Kazemi, and S. Zaroubi. GPU accelerated nonlinear optimization in radio interfer-

    ometric calibration. In 2012 Innovative Parallel Computing (InPar), pages 1–6, May 2012.


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    © ASTRON

    On Friday 6 July 2018 at 10:25am (CEST), LOFAR fully automatically responded to an astrophysical transient source for the very first time. A bight burst of gamma-rays, known as GRB 180706A, was detected by the Neil Gehrels Swift Observatory and the satellite automatically sent an urgent message to waiting facilities on the ground. In the graph at the top of the figure, the black data points show the initial flash of gamma-rays and the blue data points are the follow-up X-ray observations obtained by the satellite.

    LOFAR responded to the rapid trigger alert and a 2 hour observation started within 5 minutes of the alert. The box at the bottom of the figure shows the LOFAR monitoring system receiving and observing this source. As shown by the red shaded region, these observations cover the entire 'plateau' phase in the X-ray observations and the origin of this phase is still hotly contested for these events. Our observations may hold invaluable clues to show what is happening during this phase.

    This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester.

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    © ESO

    Prompted by the recent approval of a study to investigate options for developing the ALMA Observing Tool, a workshop was held at the European Southern Observatory in Garching on 4-6 June 2018. This brought together groups working on proposal submission tools at observatories around the world to review the current status of proposal submission systems, exchange knowledge and experience of recent developments in hardware and software solutions and to explore prospects and plans for the future development of tools and possible cooperation.

    ASTRON presented its experiences with Northstar over the last 14 years for both WSRT and LOFAR and our cooperation with many other observatories: JIVE/EVN, e-Merlin, Effelsberg, Onsala, OHP, Yebes, OPTICON, WHT/INT, JCMT, UKIRT. ASTRON was represented by Hanno Holties (not in the picture), Sander ter Veen and Adriaan Renting.

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    © None

    On the morning of an overcast and (very) windy day in June, a group of tough ASTRON and NOVA gents and lads were gathering with chattering teeth on the beach of Workum. Curious about what they were doing there? Read on - this is their story.

    So, they were standing on the beach, feeling lost and cold. All of a sudden a truck arrived, disgorging wetsuits, impact vests and helmets. Half an hour later, looking like men (and women) from Mars, in identical pink shirts, these brave people were ready for their first trial: learning to control power kites that did not want to be controlled. Once they have mastered this skill, they were ready for the second trial of the day: taming (much) bigger kites in knee-deep water.

    Ater a break and a bite to lift their spirits, our heroes ventured into the water again for their third test: body drag and upwind body drag. For the lucky ones this meant being dragged through the water by a powerful kite that had to be steered with only one hand. For the unlucky ones it involved gulping down massive amounts of water or skipping on the surface of the Ijsselmeer like flat stones.

    Those who mastered these skills were allowed to proceed to the next stage: learning to get on a board and to stay on a board. Faults were promptly punished by either falling on one's bottom or being catapulted to what felt as significant heights. The bravest and most skilled champion managed to glide for a full thirty metres, while others had to be satisfied with a meager two to three metres.

    At the end of the day, our tired but satisfied heroes were rewarded with a delicious barbecue on the beach in a very "gezellig" atmosphere (if you don't know what "gezellig" means, you should remedy it quickly - it is by far the most important Dutch word!).

    This story couldn't have been written without the contributions of Antix Sports and the ASTRON/JIVE PV.

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    © Margarida Castro Neves, ASTERICS, Heidelberg University

    The ASTERICS project organized its second European Data Provider Forum and Training Event at the Zentrum für Astronomie at Heidelberg University, Germany on 26-29 June 2018.

    This workshop convenes both researchers and engineers on the topic of on-line publishing of astronomical data and related services. It is an opportunity to identify common challenges and problems, to exchange solutions, and to share perspectives.

    ASTERICS (Astronomy ESFRI & Research Infrastructure Cluster) is an EU Horizon 2020 project that targets the common challenges shared by several astronomy facilities, including CTA, LOFAR / SKA, KM3Net, EGO / VIRGO / ET, EST, and E-ELT.

    The event is part of ASTERICS work package 4, DADI (Data Access, Discovery and Interoperability), aiming to support broad accessibility and effective archiving in data centres based on the Virtual Observatory (VO) framework.

    ASTRON was represented at this event by Rob van der Meer, Marco Iacobelli and Adriaan Renting. We presented our current efforts in enabling VO access to the LOFAR and WSRT archives, and developing the Astron Data Portal.

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  • 07/23/18--17:00: ASTRON @ Zwarte Cross
  • © JvL

    The Zwarte Cross is a big summer festival held in the Achterhoek, a region in the eastern part of the Netherlands. This part of Gelderland is mostly rural, and its culture is quite visible at the festival. The Zwarte Cross (from "black" i.e., illegal, motorcross) is the biggest music/arts festival in the Netherlands -- and also the biggest dirtbike event in the world (source: wikipedia so it must be true). A pretty special combination. This year's sold-out edition attracted over 200.000 visitors. Many "Proud to be a Farmer" tattoos were clearly visible on the large part of the audience that was shirtless in the heat. The festival is a combination of proper dirt bike races, for-fun races (mopeds, trucks, boats), music (mostly rock, but also metal, dance, gospel, country), theater, stunts -- and science!

    For all three days, the Universitent (top-left) featured a mix of 20-minutes band performances alternated by 20-minute science talks. Even drawing in a few percent of the visitors already makes for a huge crowd, and for a packed house (bottom-left), we explained Einstein's theory of Relativity. "If you want to stay young, you've got to go fast!".

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  • 07/24/18--17:00: Preserving NEWSTAR
  • © CC-BY-4.0 Tammo Jan Dijkema

    Newstar (short for The Netherlands East West Synthesis Telescope Array Reduction) is the software used for calibrating and imaging the data from the WSRT. It includes full redundancy and self calibration. A breakthrough in Newstar was the use of selfcal. With the algorithms in Newstar, it held the record of 500000:1 dynamic range for a long time.

    Newstar development started in the 1980s. Most of Newstar was developed by Wim Brouw; its most prominent user was Ger de Bruyn. Among many other achievements, Newstar was used for reducing the WENSS survey. Historical treaties on Newstar appeared in "The Westerbork Observatory, Continuing Adventure in Radio Astronomy" (Raimond and Genee, eds., 1996), and will appear in the new Westerbork book (in preparation).

    The source code of Newstar is now hosted on Github: ; the original website, complemented with scans of some manuals, is now online at .

    The installation procedure is somewhat complicated to modern standards. Docker comes to the rescue: using a Docker image of Ubuntu 8.04 (2008, code name Intrepid Ibex), we were able to create a working installation of Newstar. Running this docker image requires installing Docker (which is available on Windows, macOS and Linux), and typing the command docker run -it tammojan/Newstar.

    Using this technique, we were able to get Newstar running on the Windows 10 laptop of Wim Brouw without any problems.

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    © Francesco Santoro

    It is well known that the energy released by an Active Galactic Nucleus (AGN) is able to disturb the host galaxy's interstellar medium (ISM) deeply influencing the evolution of the host galaxy.

    The interaction between the energy released by the AGN and the ISM is particularly prominent in compact and young radio galaxies, and one of its main manifestations are jet-driven gas outflows. Compact radio galaxies are newly-born radio sources that are expanding within the ISM of they host galaxies. Many compact radio galaxies show clear signs of the interaction between the expanding radio jets and the surrounding dense, and multi-phase, ISM which slows down (or even prevents) the jet expansion. These newly-born AGN inflating their radio lobes into the surrounding ISM give us the unique opportunity to study many aspects of so-called AGN feedback.

    We studied the ISM in the nuclear region of the galaxy hosting the compact and young radio source PKSB 1934-63 (in the upper left figure) using X-shooter observations. Most of the warm ionized gas resides within a circum-nuclear disk with a radius of about 200 pc that is likely to constitute the gas reservoir from which the central black hole feeds. On the other hand, we find a bi-conical outflow of warm ionized gas that is likely driven by the expansion of the radio jets (you can see the signs of outflowing gas in the blueshifted wing of the [OIII] emission line in the central figure). Thanks to the superior wavelength coverage of the X-shooter data we could estimate the density of the gas in a more accurate way by using a more refined technique (the new diagnostic diagram we used is shown in the upper right figure). We find that the outflowing gas has remarkably high density and the AGN feedback is operating at relatively low efficiency. In addition, optical and near-IR line ratios show that the expansion of the radio source is driving fast shocks which ionize and accelerate the outflowing gas. At odds with the properties of other compact and young radio sources hosting warm ionized gas outflows, we do not find signs of kinematically disturbed or outflowing gas in phases colder than the warm ionized gas. We argue that this is due to the young age of our source, and thus the recent nature of the AGN-ISM interaction, and suggest that cold gas forms within the outflowing material and the shock-ionized outflowing gas of PKS B1934-63 did not have enough time to cool down, and accumulate in a colder phase. Last but not least, we tried to test this scenario explaining the origin of cold gas in outflows by using the information on other compact and young radio sources from the literature. As shown in the timeline in the bottom part of this daily image, this scenario is supported by the multi-phase outflows of other compact and young radio sources in the literature.

    Our work has been recently accepted for publication in A&A, you can read more about it in the paper at this link:

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  • 07/26/18--17:00: Open for Business again
  • © Madroon Community Consultants (MCC)

    The one unwritten rule in the Dinosaur Room is that we are guests of ASTRON/JIVE, so we do not publicly comment on Management any more. That is the privilege (and duty) of paid employees. But we would like to express our appreciation for the ASTRON Director expressing her appreciation by offering us a more visible spot in the building.

    We feel honoured to occupy the old room of Ger de Bruyn.

    Of course we were not unhappy in our old room, in the contemplative silence under the back stairs. We were surrounded by nice JIVE people, and even received the occasional visitor, for instance from the APERTIF commissioning team, in search of ancient knowledge.

    But we do enjoy to be back near the center of things, from where we do not have to climb the stairs to go to lunch or colloquium. We also love casual passers-by to come in to exchange a few kind words, and to listen patiently to an anecdote about the Good Old Days. But most of all, we hope to make ourself useful, and perhaps even relevant.

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    © ASTRON

    At the end of July four students of the University of Groningen visited ASTRON for a three week Honours Master project. At ASTRON the students have been working on the design, construction and test of a phased array radio telescope for amateur astronomers. With support of Roel Witvers and Peter Maat the students built a prototype radio telescope set consisting of a signal processor unit to which two types of antennas can be connected. The two antenna types can be used for observations at 300 MHz and 1.4 GHz. The 300 MHz system, which has two antennas, was used for detecting solar fringes, whereas the single 1.4 GHz antenna allowed the users to detect the galactic plane. The photo shows the students during the presentation of their project at the RU Groningen. The insets show the 300 MHz antenna (left) and three of the students at Huisje West checking the results of an observation (right).

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