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

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    © ASTRON

    One way in which the upcoming large radio surveys (line and continuum) will be used is by stacking the signal of as many as possible galaxies. This will increase the sensitivity and will allow us to derive statistical properties of classes of objects even if the individual objects are undetected. Stacking is a powerful technique to study trends between, for example, the presence of the gas and the colour, star-formation, nuclear activity of the galaxies.

    This technique has been extensively applied to data obtained by the Westerbork Synthesis Radio Telescope in the PhD work of Katinka Gereb (Daily Image 08-10-2014, see also Daily Image 26-11-2013 and 20-08-2014).

    The latest results on the characterization of the atomic neutral hydrogen (HI) content of a sample of about 1600 galaxies (with redshift up to z

    We find that the HI content is more dependent on colours, with a decreasing amount of gas going from so-called "blue cloud", i.e. galaxies dominated by relatively young stars, to "green valley" and only an upper limit for the "red sequence" where only old stars are present, and less on ionization properties of the gas in the galaxies. This is illustrated in the plot on the left. This means that regardless of the presence of an optical active nucleus (based on optical ionization line diagnostics), green-valley galaxies always show HI, whereas red galaxies only produce an upper limit (as illustrated in the plot on the right). These results suggest that "feedback" from optical active nuclei, the so called "feedback", is not the (main) reason for depleting the large-scale gas reservoirs and quench star formation.

    We also find that the radio emission in galaxies bright in infrared (IR), stems from enhanced star formation, in agreement with the finding that this group is detected in HI. However, IR early-type galaxies lack any sign of HI gas and star formation activity, suggesting that radio AGN are likely to be the source of radio emission in this population.

    This study has been used as test case and to set up the necessary software and explore the possibilities in preparation to the surveys that will be done by Apertif.

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    © ASTRON

    The ASTRON Board met in The Hague last Friday and one of the proposals to consider was the further roll-out of the APERTIF Phased Array Feed (PAF) system on the Westerbork Synthesis Radio Telescope. We are glad to report that the Board decided to support the roll out of at least 10 PAF systems on the WSRT, and has challenged the ASTRON directorate, together with the APERTIF community, to see how they can be creative in realising a full 12 PAF system.

    The roll out of the first 6 APERTIF Phased-Array Feeds is already well underway, and is expected to be complete by the end of this year. The remaining systems will be rolled out in the spring/summer of 2016. With the full system deployed, the survey speed of the WSRT for HI surveys will be an order of magnitude better than the current performance obtained from the current MFFE single-pixel receivers. The main scientific impact of APERTIF will be in the fields of galaxy evolution, transients and pulsars. The system will also eventually be available as a very sensitive phased-up element of the European VLBI Network.

    The Board's decision represents an important milestone for the APERTIF project, and we celebrate this with the image presented above. This digital artwork was created by Dutch artist, Danielle Futselaar, in collaboration with ASTRON. See for more of Danielle's illustrations, including several she has prepared for ASTRON, the SETI Institute and NASA.

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    © Natasha Maddox (ASTRON)

    Determining which points of light in the sky are stars in the Milky Way and which are quasars at cosmological distances is a difficult task, as they appear to be identical in images. The easiest way to know for certain is with spectroscopy. Choosing which points to obtain spectra of, to maximize both completeness and efficiency, is the challenge.

    The first quasar selection was based at radio wavelengths, but we now know that only ~10% of quasars are radio loud. Quasars can also be bright at X-rays, but if the central engine is surrounded by gas and dust, the X-rays are absorbed. The SDSS has used optical light to construct a catalogue of more than 200,000 quasars at redshift up to 5, but it is still missing quasars located in dusty galaxies, and quasars with unusual spectral properties.

    The near-infrared (NIR) is able to see through dust in galaxies to find quasars that would otherwise be missed by optical selection. It is also able to find quasars with strange properties, that may not look like quasars at first. Combining optical and NIR imaging, we have designed an algorithm to search through large amounts of imaging data to find quasar candidates that were missed by other search algorithms. Spectroscopy of the candidates was recently performed at the 4.2m William Herschel Telescope on La Palma, and 140 previously unknown quasars were discovered. Images of four of the new quasars and their spectra are shown in the image. Among the newly found quasars is one of the most luminous known, along with quasars with unusual spectra.

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    © ASTRON

    In September of last year, the ASTRON DESP (Digital and Embedded Signal Processing) group started an expedition. We went on a journey towards quality, transparency and enhanced employee engagement. The point of departure was that we are no longer content to wait for what is coming at us, but wish to step forward with a clear mission and vision.

    Since such principles have to be carried by each member of the group, they cannot simply be imposed top-down. Therefore we organized a "day on the heath" at an external retreat, to establish the ingredients for the group mission. It was an intensive day, with a lot of discussions and laughter. We talked about who our customers are, what needs we endeavour to satisfy, and what technology to use for that lofty purpose. But also how to distinguish ourselves, and which values and beliefs are essential in our work. Basically, the questions are "who gives us existence?" "why are we here?" and "what business are we in?". Every member of the group had a say, and continues to do so.

    We did a lot of exercises. First we held a mirror up to ourselves personally, and then to the group as a whole. This process has led, in early 2015, to the DESP Mission reproduced below. As a by-product, we also formulated some Statutes, which outline the ways in which we strive to work within the DESP group.

    The DESP Mission

    Unveiling the mysteries of the universe through the use of advanced digital systems.

    The Digital and Embedded Signal Processing group delivers digital systems to radio astronomers for retrieving astronomical information from data. With these systems we provide the optimal balance between quality and time to science.

    Involvement and focus on customers are key values for us. We communicate with each other and our customers in an open way. We are a team.

    The picture was taken by Bastiaan Spijk of HRM, who contributed significantly to the process. It shows all the members of the DESP group, clutching the Mission and the Statutes. We have already started to live by them.

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    © Ronald Halfwerk

    Steelmaker Tata Steel and the Dutch Research School for Astronomy (NOVA), signed a research cooperation agreement at the Hanover Messe in the presence of Minister Kamp of Economic Affairs.

    At first glance it seems an odd collaboration: a steel producer that works together with astronomers. Yet this collaboration is more logical than it seems at first sight. TATA Steel produces, processes and distributes high-quality steel products. The company is the fifth largest steel company in the world and uses the latest technologies. TATA Steel is looking for solutions to automatically detect very small (0.01mm) defects and contaminants in large surface areas of steel. These steel sheets are rolling of the production line at high speed.

    NOVA, the Dutch Research School for Astronomy, develops scientific instruments that monitor the night sky constantly, looking for very small changes. When astronomers observe a change, they investigate further with different types of telescopes. They unravel the light which is coming from an object, which reveals a lot of information about the chemical composition of stars and planets. Techniques used in astronomy are also useful in terrestrial applications. For example, you can detect contaminants or defects with the aid of the polarization of light.

    NOVA and Tata Steel will examine whether the techniques developed in astronomy also offer a solution for the challenges in steel production. This applies not only to the extremely sharp look, but also the super-fast processing of large amounts of data.

    In the picture from left to right: Ramon Navarro, head of the NOVA optical- infrared instrumentation division, Theo Henrar, CEO of TATA Steel Netherlands and Minister Henk Kamp of Economic Affairs.

    Science for Competitiveness is a key topic for the Netherlands 'Nationale Wetenschapsagenda'.

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    © don't worry

    On May 29 a group of Leiden students came to Drenthe to see all the interesting stuff that is happening at our facilities. About half of them were from the 2015 radio astronomy class taught by Garrett and van Langevelde, the other half were from the Kaiser association, undoubtedly aspiring to take the class in the future. The students underwent a programme of bus, Westerbork, bus, LOFAR, bus, Dwingeloo, bus, with great dedication, receiving expert explanation and other treats at all the locations. Indeed, in the end the full radio astronomy experience was accompanied with a Chinese buffet.

    Many thanks to Tom Oosterloo, Wilfred Frieswijk, Erwin de Blok, Bob Campbell, Paul Boven, Sander ter Veen, Marco Iacobelli, Wim van Cappellen, Johan Pragt for giving the presentations. And special thanks to Leah Morabito for herding the students through the day and in fact the semester.

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    © ASTRON

    The ASTRON/JIVE summer student program kicked off this week with the annual Pancake Welcome Party. The summer student program has a great international group again this year with eight students from all over the world including Chile, China, Iran, South Africa, and the US. Despite slightly mercurial weather, the sun came out in time for everyone to enjoy the fine Dutch tradition of eating pancakes for dinner. Initial estimates indicate an average pancake consumption per person of 2.5 with a few pulsar astronomers suspected of increasing the dispersion of the sample.

    In typical ASTRON fashion, the summer students had no sooner finished their pancakes before they were immediately put to work helping start a colleague's car. When asked for volunteers to help push, our new crew of summer students immediately and unanimously offered to help. With this kind of team spirit and work ethic, no doubt we can expect to see some great radio astronomy projects this summer.

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    © Rik ter Horst

    A long time ago, in the evening of March 13 1989 when going for a run, I suddenly saw strange moving colors in the clear sky and immediately I knew I had to get my camera and shoot some images of it, overwhelmed by the beauty of this Aurora Display. Now some 25 years later I thought it would be nice trying to make an animation of some of these images and I was lucky to find four successive images.

    Originaly the images were made with a Minolta camera on 400 ISO film (slides), the location was Assen-noord. Photoshop was used to make the animated GIF.

    The Aurora Borealis show of 1989 was one of the most spectacular ever, with reports coming even from the south of France.

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    © astron

    On Friday June 24, 2015, exactly 45 years, on the day, after Queen Juliana opened the Westerbork Synthesis Radio Telescope under the guidance of Jan Oort, the receivers, correlator, backend and everything else of the WSRT were shut down for the last time in a mindfull ceremony attended by many of the key players of the 'old' WSRT system. This system has been in use since about 15 years and has delivered top science on pulsars, AGN, galaxy structure, VLBI and many other topics. With this system, the WSRT was one of the world's frontline radio telescopes in the last decade. For those who care about these details: the final observations were of a pulsar whose final 'heartbeats' could be heard slipping away, followed by silence...

    As is common on such occasions, the mood was reflective and grateful for all the good things the telescope has brought in the last 15 years. Many of the attendants expressed gratitude for the privilege to have been part of it all. It was a wonderfull instrument.

    Although the 'departure' of the MFFE's, the DZB and the IVC marks the end of an amazing era, and many of us feel slightly sad about this, the actual reason to 'turn off' the WSRT is that now we can install phased-array feeds on the WSRT dishes and change the WSRT into Apertif. This will change the type of science the WSRT will be doing and will ensure it will rermain a relevant telescope in the times that we prepare for SKA....

    You should expect the first data of the new system in August.. Stay tuned... It will be fun!!

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    © University of Cape Town

    The seven-dish KAT-7 array was built as an engineering testbed for the 64-dish Karoo Array Telescope, known as MeerKAT, which is the South African precursor of the Square Kilometre Array (SKA). KAT-7 and MeerKAT are located close to the South African SKA core site in the Northern Cape's Karoo desert region. Construction of the KAT-7 array was completed in December 2010. The array is extremely compact, with baselines ranging from 26 to 185 m and the receivers have a very low system temperature of Tsys ~26 K. While its main purpose is to test technical solutions for MeerKAT and the SKA, scientific targets, such as NGC 253, were also observed during commissioning to test the HI line mode.

    The short baselines and low system temperature of the telescope make it, despite the fact that it consists of only seven 12-m dishes, very sensitive to large-scale, low-surface-brightness emission. The KAT-7 observations of NGC 253 detected 33% more flux than previous Very Large Array observations. As can be seen in the figure, HI can be found at large distances perpendicular to the plane out to projected distances of ~10 kpc away from the nucleus and ~14 kpc at the edge of the disc.

    The observations show that a large amount of HI is found outside the disk of NGC 253. The kinematics of this extra-planar gas suggests that it consists of gas blown out from the disk by the central starburst occurring in NGC 253 and by the galactic fountains in the outer parts. Analysis of the near-IR WISE data, shows clearly that the star formation rate is compatible with the starburst nature of NGC 253.

    The results of these observations we recently published in the Monthly Notices of the Royal Astronomical Society (HI observations of the nearest starburst galaxy NGC 253 with the SKA precursor KAT-7 by Lucero, D.M., Carignan, C., Elson, E.C., Randriamampandry, T.H., Jarrett, T.H., Oosterloo, T.A. and Heald, G.H.; see )

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  • 06/25/15--17:00: Afscheid Henny van Haarst
  • © Roelie

    Today we say goodbye to Henny van Haarst, who is retiring after having worked for ASTRON for 15 years. Technically, she was employed by a series of cleaning contractors (Hazenberg, Asito, ISS, Asito again and now Visschedijk), but in practice she was very much part of the ASTRON/JIVE/NOVA/DOME family. She knows more of us by name, office and occupation than any regular employee, and notices when people are absent for prolongued periods. Like us, she feels proud of the standing of our institutes in the world.

    This recent picture shows her taking her regular break outside, enjoying a quiet cigarette with anyone who would join her. With her characteristic voice, she was always ready to discuss the complexities (and occasional hardships) of keeping our working environment clean and happy.

    Thank you, Henny, and goodbye. We will really miss you.

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    © ASTRON

    Following an illness, our retired employee Cees Boon passed away last Friday, June 19th 2015. Cees worked with us since May 12th, 1997. At first through Randstad and after that as employee of ASTRON. He started as interim financial controller, then became head of Financial affairs and was comptroller until his retirement on January 5th, 2008. Cees advised the management and transferred his large financial expertise to his colleagues.

    In his spare time, he was closely connected to the checkers club HDC Hoogeveen as member and treasurer. Even when his health deteriorated, he continued visiting the club evenings.

    After his retirement Cees continued to attend the outings of the ASTRON/JIVE Personeelsvereniging, and kept on coming to the Christmas High Tea.

    Our thoughts are with his family and friends.

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    © Kelley Hess

    Galaxy clusters are the largest gravitationally bound structures in the Universe. Even after 13.8 billion years, they are still growing by accreting galaxies from their surroundings. The diffuse hot gas which fills the potential well of the clusters (which we observe in X-rays) can have an huge impact on new galaxies as they arrive: stripping the cold gas of their interstellar medium. This cold gas, observed as neutral atomic hydrogen (HI), would have been the fuel for future star formation in the galaxies.

    The grey-scale image from the Widefield Infrared Space Explorer (WISE) shows the stellar content of the Antlia Cluster (as well as many foreground Milky Way stars). The colored contours correspond to HI detected galaxies by the KAT-7 telescope in South Africa.

    The presence of HI reveals which galaxies have most recently arrived to the harsh cluster environment, and the observations show that Antlia Cluster galaxies are already gas deficient when they reach 600 kpc from the cluster center. This suggests that either the cold gas is already beginning to be stripped out of the galaxies at large cluster radii, or the gas has been 'pre-processed' in smaller gravitationally-bound collections of galaxies called groups. In fact, it appears that galaxies are being accreted on to Antlia asymmetrically from the surrounding environment, and may be coming from a filament of galaxies that connects the Antlia Cluster to the Hydra Cluster about 18 Mpc away.

    The results of these observations were recently accepted for publication in Monthly Notices of the Royal Astronomical Society (KAT-7 Science Verification: Cold Gas, Star Formation, and Substructure in the Nearby Antlia Cluster by Hess, K.M., Jarrett, T.H., Carignan, C., Passmoor, S.S., Goedhart, S.)

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    © Astron

    At beginning of June we started the LOFAR subrack assembly, flashing and testing in Westerbork. This time, we had to program all Remote Station Processing boards (RSP:78) and Transient Buffer Boards (TBB:38) ourselves. The latest firmware and CPLD code was flashed into the FPGA memories.

    For POLFAR, we assembled and tested 18 subracks in total. In parallel we are also preparing three ILT containers for the Polish LOFAR stations at Baldy, Borowiec and Lazy. The plan is to ship the first container at the end of this month. It is an intensive, but also an exciting period, and only made possible by the dedication and effort of the POLFAR team members, the DESP and TSG groups, and our external contractor Germon Offereins.

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    © NASA/DOE/Fermi LAT Collaboration

    Pulsars, rotating magnetized neutron stars born in supernovae, are fascinating objects and their study finds applications in a wide range of physics and astrophysics. By detecting pulsed gamma-ray emission from more than 160 pulsars since it began operating in 2008, the Large Area Telescope (LAT) on the Fermi satellite has revolutionized our view of the gamma-ray pulsar population and has demonstrated that pulsars form the main class of GeV gamma-ray sources in the Milky Way. Radio observations in support of the Fermi mission have provided a vital contribution to the success of LAT pulsar studies: radio searches in LAT unassociated sources have for instance uncovered several tens of new millisecond pulsars, pulsars that rotate hundreds of times every second and that constitute unique gravity laboratories.

    In this presentation I will review recent results from pulsar observations with the Fermi LAT, and discuss some implications stemming from these observations.

    The image above shows a map of the entire sky at energies larger than 1 GeV based on five years of Fermi Large Area Telescope (LAT) data. To date, the LAT has uncovered more than 3000 gamma-ray sources, including more than 1000 that have no known associations.

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    In the week of June 8 a group of mm-VLBI experts got together for a workshop on data processing and simulations for mm-VLBI, in the Snellius building of the Lorentz Center in Leiden, organized in collaboration between JIVE, Nijmegen University and MIT Haystack.

    The participants traveled from all over the world to talk about calibration, fringe finding, sparse imaging algorithms, and many more essential topics. Any effect that occurs between the source and the astronomer has to be understood in intricate detail to study the physics of mm-VLBI radio sources. This made instrument simulations a crucial topic of the workshop.

    The official programme consisted of short talks, discussion session and interactive tutorials. The fabulous infrastructure of the room encouraged an unofficial programme of informal and wide-ranging information exchange.

    The workshop ended with a discussion of future work. The participants unanimously declared that it is essential for the field of mm-VLBI to have a coherent organizational structure in place to disseminate the (currently rather fragmented and very globally distributed) knowledge of best practices in this field, and to work towards opening the field up for non-experts.

    The workshop programme and talks are accessible on the workshop website.

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    © Astron

    On the 5th of June, after a thunderstorm, we discovered a tripped earth leakage circuit at remote LOFAR station RS305. Superficially, everything seemed to work normally after powering up, but inspection of the LBA array showed something unusual. The top of an LBA antenna head had been blown six meters away from the support pole. This was clearly caused by a direct lightning strike! This offered an opportunity for verifying our theoretical models. Five years ago, we presented a paper on this subject at the EMC2010 in Wraclaw.

    The LBA damage is somewhat worse than we expected, probably due to a more complex lightning discharge pattern than we assumed in our models. In total, we had to replace 54 LBA (antennas) and 4 RCU boards. For the LBA we found open, short or clipping circuits in the X or Y polarisation. For LBA-33 (direct impact) we found that the PCB track before the Gas Discharge Tube had been vaporized on the connected RCUs. Two other RCUs had a broken transistor switch for selecting LBL or LBH input. On the positive side, none of the 288 coax cables was damaged, and this is very good news.

    Intriguingly, the signal delay communication for three HBA tiles had also failed. It was found that the modem program in the EEPROM had been erased due to high induction voltage. After re-progamming, these three RCUs worked as before!

    We will continue to study the vulnerabilities in the LBA design, also for the benefit of future radio telescopes. Part of our new knowledge and technology is already included in SKA-LFAA prototype designs.

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    © ASTRON

    Electrical engineering students from University of Twente have the opportunity to follow a master course 'Smart antennas & propagation'. This course is given by Mark Bentum (ASTRON & UT) and Gert-Jan van Werkhoven (Thales Nederland & UT). As a part of this course they have to design, construct and measure a small antenna array. Because the university does not have the proper antenna measurement facilities the students came to ASTRON to do their measurements.

    The measured antennas are patch antennas using foam as a substrate. The patches and microstrip lines are cut from conductive copper tape. The measurements are performed in the near field antenna measurement room. The measured near field is transformed to the far field by software. Michel Arts prepared the antenna measurement system in order to do the measurements and performed them.

    After the measurements Mark showed the students the ASTRON-facilities and the Dwingeloo Radio Telescope. They also went to Westerbork to see the WSRT.

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    © ASTRON

    On June 16th and 17th about 20 engineers in electronic design from industry and from ASTRON came together at the Hanze Institute of Technology in Assen to discuss quality in electronic design and manufacturing. In this seminar, organized by the Dome project, designers of highly complex electronic boards and systems shared their experience and discussed the do's and don'ts. The picture above shows the participants present on the first day of the seminar.

    Andreas Doering presented his experience with designing the highly compact Dome microserver board; Klaus Flesch shared design considerations based on his 30+ years of experience with several SME companies. Hubert Harrer presented best practices from the IBM Server Group, and Gijs Schoonderbeek discussed his experience with designing the highly complex 18-layer UniBoard2.

    The presentations and discussions made clear that several steps can be taken to increase the quality of the designs, these include careful communication, making checklists, and having a clear strategy on component library management. The discussions also concluded that the complexity of new high-end designs is enormous. This does not make it easy to reach high quality, but there are ways to get there, as the current state of the art designs show of course.

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  • 07/08/15--17:00: MFAA FrontEnD meeting
  • © Steve Torchinsky

    During the last week of June 2015, the MFAA FrontEnD (FED) work package team joined efforts on the beautiful, historical site of de Station de radioastronomie de Nancay, where we enjoyed a very fruitful meeting.

    The picture above shows (the majority of) the attendees, in front of the EMBRACE@Nancay array.

    During the meeting we discussed several items, covering all aspects of the frontend work by all partners. These developments include antenna and LNA designs, analogue beamforming, receiver, receiver control and power supply for the front-end components.

    The main goal of FED task is to design, build and verify a dual polarisation tile which demonstrates that AA technologies are ready for PDR. A tile forms the key building block for the antenna array for mid SKA frequencies. It provides all available FoV of an MFAA station which may be limited further on by processing or the available digital station output bandwidth.

    It is not required to build a full size MFAA station to predict its behavior. From EMBRACE it is known that a down scaled array consisting of 9 to 16 tiles can provide the required evidence for the behavior of a full scale array.

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