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

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    © ASTRON

    After five years of hard work at the ASTRON & IBM Centre for Exascale Technology, the Dome team presented their latest results at the Dome Symposium on May 18-19. These efforts aim at preparing for the exascale era in radio astronomy, more specifically for the Square Kilometre Array (SKA). Na�ve scaling of conventional technologies would yield a telescope requiring in the order of a gigaWatt to run, and even Moore's law will not be able to completely bridge the gap between what is desirable and what is possible.

    The Dome project therefore focused on Green Computing that addresses technologies to radically reduce the power needed to do computationally intensive work on extremely large amounts of data, Nano-Photonics that addresses technologies needed to drastically reduce the power of data transport over longer distances and inside computing machines, and Data & Streaming that addresses technologies to process data on-the-fly and store data at a high efficiency for later use.

    Indeed, with well over one hundred peer-reviewed publications, tens of architectures proposed and demonstrated in both computing and photonics, tooling created for storage and computer architecture modelling, several tens of SKA design reports produced, and by supporting an active Users Platform with thirty members, the Dome project has shown paths towards exascale, and can truly be considered a success.

    The symposium addressed all of this by giving an overview of the designs and of the data and computing challenges posed by the SKA, and subsequently zooming in into specific areas where Dome contributed and where Dome proposed designs that significantly improve efficiency. The Symposium made clear we have taken big steps towards our "dot on the horizon", but that we are not there yet.

    Symposium link:

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  • 06/11/17--17:00: Successful upgrade of CEP3

    Is this the newest building of a modern architect? Or the work of a telematic artist? No, it is part of CEP3; the computer cluster that we make available for users that want to do further processing of LOFAR data. This is a common view for our system administrators and a place where science is produced.

    The cluster is halfway its lifetime and was, like most humans do, facing a midlife crisis as it could not cope with the current demands of the users. We decided to upgrade the operating system and software frameworks to get better science output out of the investment made in this cluster.

    The upgrade went according to the planning and since last week the cluster is open again for users. Although this was one of our smaller projects, we are very pleased that we made it in time and that all planned features were installed.

    Solved another crisis and creating more happy users. That is what we stand for!

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  • 06/12/17--17:00: Building a remote station
  • ©

    Since light pollution is getting worse in Beilen, the sky brightness has risen 0.5 magnitude per square arc second in the last 5 years, I have been looking for a better location for my telescope. And I finally found it in Germany, in the back garden of friends who bought a small farm house there 8 years ago.

    When a second hand 3 meter telescope dome was offered to me by the family of a recently deceased member of our astronomy club, the decision was quickly made to relocate it to this much better location.

    During the past winter and spring a platform was built, the pier for the telescope was moved, and finally the dome was re-assembled in April with the help of many hands during a "Teleskoptreffen" (Starparty) which is held at that location. About 20 amateur astronomers from both Germany and the Netherlands gather there twice a year, enjoying both Astronomy and Gastronomy...

    At the moment the motors and automation electronics for the dome are being fitted, with that job I got help from some ASTRON colleagues. During the summer the telescope mount will be serviced by the manufacturer, and when it gets back, the telescope will be mounted in its new location.

    There it will run an autonomous observation program, starting up the observatory automatically when conditions permit, under a sky that is at least a magnitude darker than in Beilen. Stay tuned for the first light images...

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    © astron

    With data from the new radio telescopes, pathfinders/precursors of SKA slowly starting to appear, it is a good time to have a community get together for those who are interested in using these telescopes for HI absorption studies.

    This week ASTRON hosts a workshop to discuss and coordinate such surveys, with experts in the field coming from all over the world.

    The preparation for the workshop has already brought some interesting results, with the first detection, made with Apertif, of HI absorption in a distant active galactic nucleus (in this case 3C293, see figure).

    The workshop will cover science topics that can be addressed using HI absorption (intervening and associated), including what we can learn about the feedback effects of AGNs on galaxy evolution, the properties of the ISM of galaxies at higher redshift, and the cosmic evolution of HI. The workshop aims to discuss the current state of affairs as well as the progress we hope to make with the upcoming surveys, and the technical tools that are being developed to make that progress.

    for more details, have a look at

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    © Gerard Middelkoop, Dagblad van het Noorden

    The nature park around LOFAR, with its distinctive circular "moat" in the centre, attracts lots of exotic birds. But the recent visit of a group of no less than 60 Griffon vultures (Vale Gieren) was very special. Not surprisingly, it caused a flurry of excitement among the local birding community.

    Gerard Sterk and Gerard Middelkoop have placed their pictures of these "flying barn doors" on, the website for the sighting of birds that are rarely seen in the Netherlands.

    Griffon vultures normally occur in Southern Europe, North Africa and Asia. But with warm weather and wind from the South, a few of them reach us each year. They effortlessly soar with the help of rising air bubbles (thermals, or thermiek) and can cover hundreds of km per day.

    Our visitors were probably young birds, that are not yet breeding but just in search of food. They feed on carrion, i.e. dead sheep, goats or cows. These are not easy to find in our neat little country, so they soon retreat to their usual stomping grounds.

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  • 06/15/17--17:00: Mapping LOFAR
  • © CC-BY-4.0 PDOK / Tammo Jan Dijkema

    LOFAR looks best from the air. The scale is even such that sometimes the HBA tiles show up on topographical maps. I have enriched the Dutch topographical map TOP25raster with the exact positions of all LBA dipoles and HBA tiles. For comparison, I printed a recent aerial photo (which is also topographical and aerial.

    The software used for this work is QGIS, an open source GIS program comparable to e.g. ArcGIS. The files used to create this are at I will give a software talk on using QGIS for LOFAR on July 6.

    The topographical map may be used to go sightseeing all of the Dutch LOFAR stations. When doing so, please make sure not to use any RFI emitting devices such as mobile phones or cars.

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    © Paula Fusiara, Emma Baan

    In the Mechanical Group we not only design and manufacture instrumentation hardware, but we do research as well. Currently we are busy investigating the possibilities of 3D printing as a prototyping method for 3D-MID technology. One of the very important steps is characterization of the various filaments available on the market.

    As a part of her internship research at ASTRON within the mechanical engineering group, Emma Baan nicely managed to obtain an abundance of sample filaments from many suppliers. However, one of the suppliers stunned us to such a degree that we would like to thank them a lot for such an awesome customer support!

    Although the supplier did not confirm that they would send the samples, one day Emma did receive a mysterious parcel from the UK.

    You can imagine the feeling when you get something that you do not know what to expect ... Emma hesitantly tore the grey foil open, and a smile appeared on our faces because we saw the awesome-looking package from Rigid.Ink, the filament supplier. The smiles broadened even more when we read the description on the bag. But the content of the kit together with the READ ME note amazed us completely.

    Emma received a set of different filament materials together with informative description on the manufacturing conditions under which the filaments should be used; not to forget a small bag of well-known jelly sweets! All of this thanks to the highly trained support ninjas from Rigid.Ink and Ed, the most entertaining Office Astronaut we have ever had contact with!

    We give them big thumbs up and a huge thank you for such a nice customer support!

    Joyful greetings from both of us, the Mechanical Ninja Paula and Mechanical Ninja-in-Training Emma!

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  • 06/19/17--17:00: Ghosts on the moon??
  • © Rik ter Horst

    Some time ago I was visually observing crater Tycho with my 400 mm telescope and at some point I was hindered by something that looked like a kind of reflection just in the middle of the black crater floor of Tycho. Then it came into my mind that I might actually be observing the central hill of Tycho indirectly lit by the bright crater rim! I decided to take an image of it and after some processing it was very clear that this was indeed the case. You can even see shallow hills on the crater floor on the processed image.

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    © ASTRON

    LOFAR supports a wide variety of science cases, but in some parts of the year only a few related projects take over. These several weeks, it is pulsar observing time!

    The image shows the LOFAR observing schedule from June, 12th-20th with 44 (light/dark) green blocks, 42 of which are for various pulsar observing projects. Several CEP4/COBALT/DRAGNET test reservations in white are preparations to further improve observing capabilities for pulsar studies. Stay tuned!

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    © ASTRON, 2017

    As part of the revision and upgrade of the Westerbork Synthesis Radio Telescope (WSRT), the hardware and software of the telescope control system have been completely redesigned. With that, the WSRT is fully prepared for the new APERTIF era.

    To operate and commission APERTIF properly, the telescope control system should be able to support holography(*). In this mode, one dish tracks a source continuously, while the other scans the same source using a predefined scan pattern. This mode was available in the former WSRT telescope control system, but was not ported to the new system yet. We are glad to report that the holography mode has recently been implemented in the new system as well.

    The implementation of the holography mode should of course be verified. How could that be easier, when you just installed Phased Array Feeds in the WSRT dishes? The above images show the 121 receiver chains for dishes RTA and RTB. RTA (left) scans a bright radio source, while RTB (right) tracks it. The scan pattern used here has four points. You can clearly see that the bright source moves through the different receiver chains (or 'pixels') in the left panel. In the right panel, the bright source is in the centre at all times. This shows that the new telescope control system now successfully support holographic measurements.

    (*) In radio astronomy, holography is a technique to measure the shape of the dish(es) with the help of a strong celestial point source. It was originally implemented for the WSRT by Hans van Someren Greve.

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    © ASTRON, 2017.

    On June 8 and 9, 2017, the SKA Organisation, ASTRON, MFAA, PAF and WBSPF consortia had a meeting at ASTRON in Dwingeloo to consider new technologies that can improve the scientific capabilities of the SKA beyond Phase 1, and to discuss the structure and timescales of the SKA Advanced Instrumentation Program (AIP) and its successors.

    Currently, the AIP includes consortia on Mid-Frequency Aperture Arrays (MFAA), Phased Array Feeds (PAF) and Wide-Band Single Pixel Feeds (WBSPF). These consortia are executing research and development programs to demonstrate feasibility and increase maturity of their respective technologies for application in the SKA.

    The workshop had 37 registered participants and included a series of talks on how new technologies will vastly improve the scientific prospects for SKA, a session on the SKA Observatory Development Program, a session on the status and plans of the current MFAA, PAF and WBSPF consortia, and several technical talks by these consortia.

    One of the main conclusions of the meeting is that, since the SKA Observatory is setup for a 50 year lifetime and will offer world's biggest radio telescope, continuous upgrades and expansions, enabling new capabilities, are essential for the future of the SKA.

    All presentations of the meeting, including a wrap-up of the discussions, can be downloaded from the meeting website:

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    © Zsolt Paragi

    The 2017 ASTRON/JIVE summer students have arrived!

    This year we are hosting seven students from all around the world. From left to right on the picture are Nivedita (India), Ann (Kenya), Mel (US), Chen (China), Yennifer (Colombia), Emma (UK) and Avni (India). Please give them a warm welcome.

    A brief description of the projects the students are working on can be found at

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    © ASTRON

    One of the ways to explore gas in the Universe is using HI absorption observations. The new radio telescopes (ASKAP, MeerKAT and Apertif on the WSRT) offer exciting new possibilities for science using HI absorption. Coordinating the groups planning to exploit these data was one of the motives for a small but very lively workshop held at ASTRON 14th to the 16th of June 2017.

    HI absorption observations are complementary to those tracing the HI gas in emission because they allow to detect gas much distant objects and to image the gas at very high spatial resolution, i.e. at parsec scales reachable by VLBI.

    The workshop covered a number of important topics, from the status of the new (or upgraded) telescopes, and of the tools to exploit the upcoming surveys, to the science we want to do with the data and the complementarity of the various surveys.

    The schedule of the workshop included ample time for discussion. Each session had presentations of participants and was followed by a discussion about open issues. A number of action points have been decided, hopefully providing a better coordination among the various groups. The perfect weather also helped in making sure the discussions could continue outside the building. About forty astronomers attended the workshop, coming from eight different countries (with particularly large groups from Australia and India). About 1/3 of the participants were female and about half were young postDocs and PhD students. In short: a very lively community ready to start exploiting the data beginning to appear from all telescopes including Apertif (see Daily Image 14-06-2017).

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    © -

    The Leiden Radio Astronomy course for Master students is a serious business. It takes 14 lectures to follow the waves through the processing chain, from currents in the antennas to carefully calibrated images, and then to interpret these in terms of astrophysical processes.

    In addition the students get tutorials in casa and defining radio observations. Next they work on assignments in which they process and interpret a real (unpublished) astronomical data set. This year's edition was covered by the baseline between Huib_I & Huib_J in order to get full coverage. In addition there was teaching assistance by Josh & Jit and a number of ASTRON staff provided guest lectures. This did get the students to the (almost) final stage on June 1: the Drenthe field trip of radio facilities.

    Thanks everybody for the help and students, all the best with your studies!

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    © N. Maddox (image credit: Di Matteo, Springel & Hernquist)

    Feedback from accretion onto the supermassive black hole at the centres of galaxies is often invoked to explain many characteristics of galaxies. Indeed, this feedback in the form of galaxy-scale outflows is required in simulations to stop galaxies from growing too large, too quickly. However, observing this process in luminous quasar systems is difficult.

    The Herschel Space Observatory has observed large areas of sky at far-infrared (FIR) wavelengths, which measures emission from dust in galaxies. Using a large sample of SDSS quasars that have also been observed with the Herschel Space Observatory, we find that quasars that are bright in the FIR also show signs of strong outflows originating from the nuclear black hole region. This indicates a connection between quasar activity, which occurs at the nucleus of galaxies, and galaxy-scale processes such as star formation.

    The result is only now possible due to the availability of new, very accurate measures of the quasar redshifts, and large-area FIR surveys. This work has been accepted for publication in MNRAS, and can be found on the arXiv at 1706.04789.

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    © R. PIzzo

    From 19-23 June 2017, the conference 'The Broad Impact of Low Frequency Observing' took place at the Conference Center of the INAF/CNR research campus, in Bologna (Italy).

    The programme covered highlights from low frequency observations obtained with a range of radio observatories around the world. These are significantly impacting science areas including the Epoch of Reionization & Cosmology, Pulsars, The Milky Way and Nearby Galaxies, AGN, Star Formation, Clusters, Sun, Ionosphere, Cosmic rays, and Transients.

    The science talks as well as the special session on Instrument & algorithms provided a comprehensive overview of the versatility and state-of-the-art technical capabilities available at low frequencies. With LOFAR unmistakably in a world-leading role, it is clear that the breadth of all available observing facilities and data analysis techniques together is contributing to the broad science impact being made.

    The meeting was an important opportunity to discuss the planned upgrades to LOFAR and the other current facilities, looking ahead also to how these will complement the SKA-low in the years to come.

    On Friday afternoon, the ASTRON Radio Observatory held the 4th LOFAR User Meeting, at the same location. The meeting provided a forum for users to both learn about the status of the array as well as give feedback on LOFAR operations and development. Among the important enhancements introduced in the system, the addition of new international stations to the array, the introduction of new software functionality into the operational system, and new techniques to improve the quality of LOFAR images were presented. The LOFAR Users Committee summarised the experience of the community about using the system. The Radio Observatory answered questions and gathered a lot of important feedback that will be used to improve the user experience during the coming months.

    200 participants attended the events in Bologna. Shown here is the conference picture taken at the conference venue. The conference was jointly organized by ASTRON and IRA/INAF, with financial support from ILT, IRA/INAF and RadioNet.

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    © ASTRON

    Almost 2 years ago the DRAGNET project acquired a GPU cluster to search for pulsars and other fast transients. The intended use was also to directly take correlator/beamformer data during an observation. All integration with Radio Observatory software systems needed for smooth operations has now been completed and commissioned. While some of our projects continue to observe to CEP4, we can utilize more observing time at minimal Observatory effort by observing directly to DRAGNET. Data access during observing can also be used for very early data reduction and event detection.

    In the image the orange arrows on the left indicate the data flow from antennas through COBALT to CEP4 or DRAGNET. The purple arrows show monitoring and control interactions. In particular, software running on the Support systems and databases (DBs in red) had to be adjusted without breaking existing functionality.

    The small plots at the bottom show CPU and cluster network workloads over 24 hrs. DRAGNET should be able to handle twice the usual "full" data rate (green spikes). In the final tests we did 2 short test observations at full data rate on the bright pulsar B1133+16 and on the millisecond pulsar J2145-0750. The observations finished correctly without data loss. Cees Bassa processed the data. The "presto" plots from J2145-0750 on the right show a very clear detection from 6 stations after 15 minutes.

    DRAGNET has discovered 3 millisecond pulsars to date in an offline mode (e.g. Bassa, Pleunis & Hessels 2017). With DRAGNET in operations, we aim to greatly increase this yield, and the first such observing proposal has been submitted!

    This project has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013) / ERC grant agreement nr. 337062 (PI Hessels). J.W.T.H. acknowledges funding from an NWO Vidi fellowship.

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    © ASTRON

    The Netherlands China Long Wavelength Explorer (NCLE) is a radio receiver aimed at observing the low frequency radio sky in lunar (Earth-Moon L2) orbit. NCLE is still in the design phase, and is geared to launching with the Chinese Chang'e 4 relay satellite in 2018.

    In May 15-16 the NCLE teams presented their designs at the preliminary design review (PDR) at ESTEC. The ASTRON team showed readiness to proceed to the next phase of the project for the analog parts of the system: the analog input system, the calibrator board and the low noise amplifier. All showed technology readiness levels up to TRL 6. In addition, prior to the PDR, conductive and radiative EMC measurements were carried out with NCLE mock-up antennas mounted to a model of the Chang'e 4 spacecraft. Indeed, although the measurements are not complete yet, it is clear that there are significant EMC background signals present. The measurements however confirmed the validity of our linearity approach that includes switchable attenuators and frequency band selection.

    The picture shows in counter clockwise order a drawing of the Chang'e 4 spacecraft with the three 5 meter monopole antennas mounted to it, one of the spectral filters designed for band selection, an infrared image of the board that produces narrow pulses for calibration purposes, an analog input board selecting input bands, NCLE antenna mock-ups and a measured EMC spectrum, and an impression of the PDR meeting. Currently we're heading full speed towards finalizing designs, and after that to start production.

    The NCLE receiver project is a collaboration between ASTRON, Radboud University (PI), Innovative Solutions In Space (ISIS), the Chinese NAOC, and is supported by the Netherlands Space Office (NSO).

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    © ASTRON, 2017

    We have been reporting on fringes every now and then to show the improvements in our new Phased Array Feed (PAF) system, APERTIF. The first daily image with fringes dates from 2008, showing the APERTIF precursor. Three years ago we used APERTIF hardware for the first time. At the end of 2015 we celebrated the first light of the APERTIF correlator. As of today, we are not going to show many fringes anymore. The APERTIF system is maturing and now the delay compensation stops the fringes!

    This daily image shows a fringe during the first 260 seconds of the observation. After 260 seconds, the delay compensation is activated and the angle of the correlation becomes constant in time (see lower panel). From that moment, all fringes are stopped. The top panel shows this for a bandwidth of 135 MHz and for two dishes that are 576 metres apart. Similar results were achieved with dishes RT2 and RTB, which are almost 1200 metres apart. With delay compensation in place we can now perform sensitive astronomical observations and do various validation tests.

    A short explanation of fringes:

    For an interferometer such as the Westerbork Synthesis Radio Telescope (WSRT), the relative times of arrival of a signal at the dishes depend on the position of the source with respect to the telescope. Due to the rotation of the Earth, the position of the source, as seen from the perspective of the telescope, changes over time. These varying delays cause fringes in the observed signals. The detection of the first fringes is always a cheerful moment, but actually these fringes are undesirable. To stop the fringes, the varying delays between the dishes need to be compensated in real-time. In APERTIF, this is performed in two stages. Coarse delays are compensated by introducing an integer sample delay in the digital signal processing chain. Delays smaller than one sample are compensated by applying a phase gradient over frequency, also in the digital domain.

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  • 07/05/17--17:00: Today and tomorrow: WimSym77
  • © ASTRON

    Today and tomorrow we honour Wim Brouw with a 2-day symposium.

    The program can be found here:

    The talks may be followed via the link:

    NB: Geinteresseerde collega's van ASTRON, JIVE, NOVA en DOME kunnen uiteraard gebruik maken van de overblijvende stoelen in het auditorium wanneer alle gasten hebben plaatsgenomen.

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