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

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    © Rebecca Azulay

    We present a study of the radio emission and kinematics of a sample of stars belonging to the AB Doradus moving group through VLA and VLBI observations at frequencies of 5 and 8.4 GHz. The main aim of our study is to obtain precise estimates of the dynamical mass of young, low-mass stars, which in combination with photometric measurements provide precise benchmarks for calibrating pre-main-sequence (PMS) stellar evolutionary models.

    Calibration of PMS models appears essential as they are widely used to predict the masses of low mass objects as brown dwarfs and planets.

    Previous studies show that model predictions are in disagreement with experimental results, underpredicting the dynamical masses by 10-30%, for masses below 1.2 solar masses. Among the stars included in our study, we emphasize the results obtained in two of them: AB Dor B and HD 160934.

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  • 03/16/17--17:00: APERCAL Unleashed!
  • © ASTRON

    On 27/2-1/3, the Apertif Commissioning survey team had the first Busy Weak, organised by Danielle Lucero and Bjorn Adebahr.

    There were two main goals.

  • The first goal was for every member of the team to be able to get familiar with the environment in the Happili cluster (where the Apertif imaging data will be processed) and run the pipeline.

  • The second goal was to actually test the selfcal part of the Apertif imaging pipeline, Apercal.

    Apercal is the result of the work of Bjorn Adebahr (and before him Brad Frank and Nicholas Vilchez) under the supervision of Tom Oosterloo. It is a Miriad-based pipeline which should produce images and line cubes for the imaging surveys that Apertif will carry out. Thijs van der Hulst, Joris Verstappen and Mike Sipior have been preparing the Happili cluster to run the pipeline.

    The commissioning members familiarised themselves with the self-calibration and imaging pipeline by working through the provided tutorials and also by using a WSRT data set of 16 pointings of the Lockman Hole area. The fine tuning of the parameters is still in progress, but the results are very encouraging and good images were obtained.

    The figure shows one of the images obtained during the BW, reaching 15 microJy/beam noise and full resolution of about 10 arcseconds. The whole cycle (selfcal and imaging on 16 WSRT pointings, roughly corresponding to one Apertif observation) can be done within one hour on one Happili node. Using all nodes would reduce this to 20 minutes (the time required for a single field).

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    © Mark Bentum

    The IEEE Aerospace conference is the biggest conference in the field of Aerospace Engineering in the world. Over 800 attendees from academia and industry come together every year in the beautiful place of Big Sky in Montana, USA. In this six day conference over 450 papers are presented.

    This year, a team of the University of Twente and ASTRON won the prestigious best paper award. The awarded paper, Frequency Smearing in Full 3D Interferometry, explores the effects that frequency smearing has in the case of a 3D mode of operation, and it is shown to be different from traditional 2D imaging, because the resulting map does not get smeared. A framework is developed to optimize the sensitivity of the telescope in light of the limited achievable data rate to Earth by making a trade-off between decorrelation and observation bandwidth. Simulation results are presented using the Orbiting Low-Frequency Antennas for Radio Astronomy (OLFAR) concept as a case study.

    The paper is authored by Pieter van Vugt (University of Twente), Stefan Wijnholds (ASTRON), Arjan Meijerink (University of Twente) and Mark Bentum (ASTRON & University of Twente).

    The was the first time an European team won the best paper award and the second time in a row that the best paper award was won in the section on Radio Astronomy and Radio Science, organized by Mark Bentum.

    The picture shows the award, the congratulations by the organizer (from left to right: Pieter van Vugt, Mark Bentum and Bob Minnichelli from the Aerospace Company), and a nice view of the location of the conference.

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    © Rik ter Horst

    This image shows the central area of the Orion Nebula, one of the most magnificent astronomical objects visible at the night sky...

    A 40 cm F/3 Dobsonian telescope has been used to catch this display, together with a new ASI178MC camera. For this image I've stacked 1000 frames with one second exposure for each frame. This 'lucky imaging' technique makes it possible to reduce the effects of air turbulence or errors in the telescope drive, improving resolution of the image considerably.

    Despite living just north of Groningen, the city lights didn't bother me too much obviously ;-)

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  • 03/21/17--17:00: Cloudify Casa with Jupyter
  • © Aard Keimpema, Des Small

    The size of astronomical datasets has increased dramatically over the years; terabyte sized datasets are no longer an exception. This trend will only accelerate; the SKA is expected to produce nearly 1 TB of archived data each day. This means that it will no longer be feasible for astronomers to download these huge datasets and perform the data reduction on their own machines, as is currently the practice. Instead the data reduction is likely to be done close to where the data is archived in central data processing centres, with the astronomer operating remotely on the data.

    One way of facilitating this is through Jupyter notebooks . Jupyter is a web-based application which allows users to create interactive notebooks which can include annotated text and graphics as well as executable code. Currently Jupyter supports more than 40 different programming languages, including Python, R, and Matlab. Jupyter is designed be extended and makes it easy to add additional languages.

    As part of the Obelics work-package of the EC-funded Asterics project we have created a Jupyter kernel for CASA, a widely-used software package for processing astronomical data. The kernel allows all CASA tasks to be run from inside a Jupyter notebook, albeit non-interactively. Tasks which normally spawn a GUI window are wrapped so that their output is saved to an image instead, which is then displayed inside the notebook. The Jupyter kernel requires a custom build of CASA which we will distribute together with the kernel in a Docker image .

    The notebook format also has the great advantage that all steps of the data reduction are preserved inside the notebook. This means that the whole data reduction process is self-documenting and fully repeatable. It also allows users to very easily make changes to their pipeline and then rerun the pipeline steps affected.

    The figure shows a Jupyter notebook of the CASA 3C391 VLA continuum tutorial running inside a web browser on a tablet.

    ASTERICS is a project supported by the European Commission Framework Programme Horizon 2020

    Research and Innovation action under grant agreement n. 653477

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    © Micha�l de Becker

    Massive stars are extreme stellar objects whose properties allow for the study of some interesting physical processes, including particle acceleration up to relativistic velocities. In particular, the collisions of massive star winds in binary systems are adequate environments to accelerate notably electrons involved in synchrotron emission. This leads to their identification as non-thermal radio emitters. To date, this has been demonstrated for about 40 objects.

    The relativistic electrons are also expected to produce non-thermal high-energy radiation through inverse Compton scattering. This class of objects permits thus to investigate non-thermal physics through observations in the radio and high energy spectral domains. However, the binary nature of these sources introduces some stringent requirements to adequately interpret their behavior and model non-thermal processes. In particular, these objects are well-established variable stellar sources on the orbital time-scale. The stellar and orbital parameters need to be determined, and this is notably achieved through studies in the optical domain.

    The combination of observations in various spectral domains is thus the key to investigate these particle-accelerating colliding-wind binaries, and achieve a clearer view of their role in stellar and galactic astrophysics.

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    © Paul Groot

    The MeerLICHT telescope - prototype for the BlackGEM array - is currently being tested on-sky at the Radboud University in Nijmegen. The telescope was built by the NOVA Optical-Infrared Group at ASTRON.

    The graph shows the signal-to-noise ratio as a function of the brightness (SDSS) of the source in a 1-minute integration, for the telescope's six different colour filters. A limiting magnitude of 20 was reached in a 1-minute exposure in the broad V+R band (dark grey points), with a 3.5 arcsec seeing and during full moon.

    Extrapolating to the conditions at the La Silla Observatory - where BlackGEM will be installed to search for counterparts of gravitational wave sources - it was concluded that the telescope will reach its design specification to detect 23 mag stars in a five minute exposure!

    Next month, the MeerLICHT telescope will be shipped to South Africa to be installed at SAAO's Sutherland observatory. It will always co-point with the MeerKAT Radio Array, to simultaneously search for transients and variable sources in optical and radio.

    NOVA's final design review of the BlackGEM project takes place in Nijmegen on Thursday 23 and Friday 24 March.

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    © RO, RUG CIT

    On January 19th, we celebrated the delivery of our new CEP4 cluster of computers. It replaced the CEP2 cluster, which has been used to process LOFAR data from April 2011 until December 2016, i.e. about 5,5 years. Not many tears will be shed for CEP2, as it had a painful start and was long plagued by production faults. But in the end we managed to stabilize its operation; the last year of its service was the best.

    So what happens with the old CEP2 cluster?

    Last December we contacted three recycling companies, of which Solid Circle from Waalwijk made the best offer. We asked them to pick up the 108 CEP2 systems and also about 40 old LCU's of the Dutch LOFAR stations. They were particularly happy with the 1200 disks of 2TB each, and most systems will be checked and refurbished.

    Refurbishing these machines is of course good for the environment although their power consumption is substantial! The company carefully registers all systems, even the very old ones, and all disks are completely erased by means of a certified method.

    On January 12th, a team of six people from Solid Circle, RUG-CIT and ASTRON emptied the nine racks of the CIT location "Landleven". Trolley after trolley with hardware rolled out of the data center towards recycling. A special Thanks to Kees Visser for all the years of teeth-gnashing care for this unruly workhorse.

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  • 03/27/17--17:00: The heart of the Soul Nebula
  • © Albert van Duin

    The Soul Nebula, AKA Westerhout-5, Sharpless 2-199 or LBN667, is a big star forming region in the constellation of Cassiopeia. W5 is a radio source within this nebula. But this image only shows part of it, a interesting piece about the apparent size of the full moon, while the complete nebula complex spans about four full moons. Its distance is estimated at 7500 light years. Another big star forming region located in Cassiopeia is the Heart Nebula, and together they are popular targets for astrophotographers, since they will fit in one image with wide field optics.

    In this image, red shows glowing hydrogen gas, but there are also some blueish reflection nebulae visible as well as a few dark dust clouds. Total integration time was 4.2 hours with a 0.4m reflector equipped with a cooled CCD camera, through RGB and Luminance filters.

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    © JIVE

    The JIVE Uniboard Correlator (JUC) is an FPGA-based correlator that can correlate two polarizations of four 16 MHz subbands for 32 stations on a single board, among other modes. The correlation engine is now well-tested and the commissioning process proceeds apace.

    The Uniboard correlator's low power consumption and high data throughput makes it a very attractive candidate for eVLBI operations, and now that we are confident of the quality of its data products we are working towards tests of that functionality in the near future.

    We have correlated a single 2.5-min scan of J1955+5131 from a recent EVN observation at 6 cm with seven stations: Effelsberg, Medicina, Noto, Onsala, Tianma, Zelenchukskaya, and Badary. We correlated the data with both the production SFXC software correlator and the JUC FPGA correlator, with eight subbands of 1024 channels each. The output signals after correlation agree within 1%.

    The image shows the final images obtained from this scan with the two correlations. It can be clearly seen that both images are identical, showing a compact source with a peak brightness of 5.16 mJy/beam and a noise rms level of 0.39 mJy/beam. The synthesized beam is 3.9 x 0.86 mas, and contours start at 3 times the noise level with increments of square root of 2.

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    © Claudia Cicone

    The cold phase of the interstellar medium has a central role in galaxy growth and evolution. In normal galaxies following the so-called "main sequence" of star-forming galaxies, the star formation rate is believed to be regulated uniquely by the amount of gas available, and more specifically by the mass of cold and dense molecular gas. Despite the enormous efforts to trace molecular gas in larger and larger samples of galaxies, at multiple scales and at multiple epochs, nearly all of our empirical knowledge of scaling relations linking molecular gas and galaxy properties is still based on observations of massive (e.g. M*>10^10 M_Sun), metal-rich and gas-rich spirals. There is therefore a strong motivation to test molecular gas scaling relations over a much broader dynamic range of galaxy properties.

    With this goal in mind, we have undertaken the 'APEX low-redshift legacy survey of molecular gas (ALLSMOG)', a survey of CO(2-1) line emission in a sample of ~100 star forming galaxies in the local Universe, characterised by stellar masses, SFRs and gas-phase metallicities significantly lower than have been probed by previous CO observations.

    The survey was completed in early 2016 and the final data products will be released soon (Cicone et al. submitted). I will present our latest results based on the full ALLSMOG dataset.

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    © Delpher

    Many evenings can be spent browsing around in Delpher,, a site with historical Dutch newspapers, for example looking for old news regarding the Dwingeloo Telescope. In this image we present some findings from the period 1953 - 1955; the years before the Dwingeloo Telescope was opened.

    We leave it as an exercise to the reader to search for similar images regarding the construction of the WSRT, and submit their own collage as a daily image.

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    © INAOE

    INAOE is official partner within the WEAVE project and responsible for producing optics for the Spectrograph.

    Last week, they started the polishing of the large (670 mm diameter) spherical mirror of the Spectrograph Collimator.

    Other optics are also in production and they already finished 3 lenses for the "Red camera". There are 4 to go for the Red, and another 7 for the Blue Camera.

    INAOE is an institute in Mexico combining astronomy and technique. They operate their own radio telescope (mm wavelength) in Mexico and participate in e.g. the GTC optical telescope at Canary Islands. This sounds familiar to me: they are the Mexican version of ASTRON.

    WEAVE is a new multi-object survey spectrograph for the William Herschel Telescope (WHT) on La Palma, in the Canary Islands. WEAVE is being built by several institutes in several countries. The Spectrograph team is led by Johan Pragt, NOVA. Dutch PI is Scott Trager, Kapteyn Astronomical Institute, RUG.

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    © MRATHS

    Some of you may recognize the telescope above as having the same design as the Dwingeloo Radio Telescope (DT). This is correct; the design of the DT was exported to the UK, where Dr Hey, of the Royal Radar Establishment, built an interferometer based on two Dwingeloo Telescopes. Unlike the original, the telescopes in Defford (close to Malvern) are placed on rails to form a baseline with length up to 1 km, either East-West or North-South.

    One of the telescopes is still there. It has been fitted with a tripod, and currently is part of E-MERLIN.

    The image above was part of an exposition of the Malvern Radar and Technology History Society (MRATHS) in 2016.

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    © Menno Schuil

    An octopus with vacuum tentacles holds aluminium plates during milling of the WEAVE spectrograph parts.

    Already 80 plates are produced with the octopus.

    The octopus is invented, designed and produced by Menno Schuil.

    Check out the movie with spider in action: it shows the de-burring of one of the plates by a 5 axis simultaneous movement of our milling machine.

    Programmed and produced by again Menno Schuil.

    The design of the plates is by Niels Tromp.

    At the end those plates will form the collimator unit for WEAVE.

    WEAVE is a new multi-object survey spectrograph for the William Herschel Telescope (WHT), on La Palma in the Canary Islands.

    WEAVE is built by several institutes at several countries.

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    © Artist impression of the Athena mission (courtesy ESA)

    Athena is the ESA mission to study the Hot and Energetic Universe. It has been selected as second large-scale mission for a launch in 2028. The science is concentrated around the formation of large scale structures from the formation epoch to the present time (these structures have typical temperatures of 10^5-10^8 K and is therefore called the Hot Universe) and the study of the complete history of black hole evolution and its related physical processes (the Energetic Universe). In addition, it will return a wealth of data for many other areas of astrophysics.

    The mission is based on a high-angular resolution mirror with a collecting area of 2m^2 at 1 keV and two instruments: a Wide field Camera which will enable a survey down to 2.7x10^-17 erg/s/cm^2 (over several degrees during the mission life-time) and an X-ray Integral Field Unit which allows high spectral resolution imaging over a modest field of View. The Netherlands is one of the major contributing countries: the technology for the mirror and for the read-out of the X-IFU detector has been pioneered in the Netherlands.

    I will describe both the science capability as well as the instruments of Athena.

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    © ASTRON

    Wednesday 5 April we had our yearly R&D team outing. This year we went to Ljouwert, the Capital of Fryslan province! Our organizing committee, consisting of Arthur Coolen & Martijn Brethouwer arranged an exclusive excursion to NEWAYS Leeuwarden.

    NEWAYS specializes in development, engineering, production and distribution of electronic products. At arrival we were warmly welcomed with coffee and fryske oranjekoeke. After this warm welcome, we suited up in ESD clothing to have an exclusive tour into the innovative world of automated assembly of micro-electronics. We followed all the manufacturing steps up to a fully populated printed circuit that complies with required IPC* quality standards. All the essential steps like paste stencil manufacturing, automated pick and placement and checking with the AOI* were explained in great detail by the NEWAYS staff.

    After the tour we walked to the Elfstedenhal for a presentation by Hans Ketelaars. We received a great presentation of the capabilities of NEWAYS technologies company, and a nice discussion followed on technology development and the capabilities of the NEWAYS holding.

    A delicious lunch was served, and after a goodbye to the NEWAYS staff we went bowling in the Grote Keizer! It was time for some leisure and we split up into teams and played ten-pin bowling. The combination of good throwing skills and accurate pointing is required to get a strike, the ultimate score at every throw. A lot of different throwing styles were used to get a strike, but somehow these radio guys can point pretty well. (3 of the 4 top ranked players). Must be the daily work with analog beamforming concepts. Anyway it was great, I think this was a great and joyful outing of the R&D team. Thank you all.

    IPC = IPC Association Connecting Electronics Industries

    AOI = Automated Optical Inspection

    PS: Mark Ruiter ended up as ultimate winner being "best bowler of the R&D department 2017"! Albert-Jan Boonstra won "the most average player prize" en Sarod Yatawatta won the "encouragement prize"...

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  • 04/09/17--17:00: Vapour Phase Soldering
  • © ASTRON

    Currently, the R&D department is assembling some prototype PCB's (Printed Circuit Boards) for the NCLE project. Some of the components however, are hard to solder by hand because all solder pads are located on the bottom side of the component. Usually these components are soldered in an automated reflow process, but for a prototype, outsourcing gives a lot of overhead and time loss. Soldering them by hand with a hot air pencil is an option, but both component and board are easily overheated and thus damaged, because the PCB contains 4 layers with a lot of copper that conducts heat away from the solder location. So a lot of heat has to be applied to the solder location.

    However, since a few months we have access to a so called Vapour Phase soldering unit. This has a lot of advantages over the previously mentioned soldering techniques. To solder components with this machine, we first have to apply solder paste to the solder pads on the PCB. This is done by hand using a dispenser, or by using a solder paste stencil with holes. Next, we place all components on the solder paste, and finally we put the PCB on the rack inside the Vapour Phase unit's tank. On the bottom of the tank is a small amount of a special inert Fluorcarbon fluid, Galden 230 or 210. When this fluid is heated by the machine it evaporates, the vapour rises to the level of the PCB. The vapour starts condensating on the "cold" PCB and components, heating them to the desired temperature (230 degrees for lead/free and 210 degrees for lead solder). As soon as the PCB reaches this temperature the solder paste reflows and the components are soldered. Then the vapour rises even further and reaches a sensor that automatically switches off the machine and starts the cooling process. The complete cycle takes about 15 minutes.

    In this way it is feasible to reliably solder PCB's with "difficult" parts, even for space applications, something which is much harder to accomplish when soldering manually.

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    © JIVE

    On 4th April JIVE welcomed a group of just over 40 people from the TU Delft Department of Space Engineering to Dwingeloo. The visit was part of the continued collaboration between the TU Delft and JIVE. This collaboration covers a range of exciting space and planetary science missions and projects, specifically those that benefit from ultra-precise tracking of spacecraft. These include several operational missions, like the ESA's Mars Express and Russia-led Space VLBI mission RadioAstron, as well as the ESA's prospective flagship mission JUICE (Jupiter Icy Satellite Explorer) scheduled for launch in 2022.

    Together, JIVE and the Astrodynamics and Space Missions group of the TU Delft have developed a wide range of methods based on the so-called near-field VLBI technique. Its applications cover very diverse science topics, from diagnostics of the planetary atmospheres by radio occultation experiments, to studies of planetary bodies' gravitational fields, and fundamental physics experiments with space-borne ultra-stable quantum oscillators.

    The group were given a brief introduction to JIVE as a European Research Infrastructure Consortium by Huib Jan van Langevelde, and research and development at ASTRON by Jan Geralt bij de Vaate. Following this the group was divided in to two and guided by Ilse van Bemmel and Giuseppe Cimo around the JIVE correlator (hosted by Bob Campbell), and the venerable 25m Dwingeloo radio telescope (courtesy of CAMRAS: Paul Boven and Tammo Jan Dijkema). The group completed their tour with a trip to Westerbork, led by Leonid Gurvits, to visit the WSRT (courtesy of ASTRON) and the Herinneringscentrum Kamp Westerbork.

    Hopefully, the guests have fond memories of the tour, especially the most beautiful Spring weather (which, as we all know, is always the case in Mooi Drenthe).

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  • 04/11/17--17:00: TMS III is out!
  • © TMS

    In 1995, the new head of ASTRON R&D blithely suggested that we should write an update on the Bible of our trade, which had appeared in 1986. Since we had LOFAR and SKA to build, we had the sense to recoil from such a gargantuan task. But fortunately the three authors (TMS) themselves produced an updated 2nd edition in 2001, and now a 3rd. It is available as Open Access book (hard copies can be bought as well). You can download a PDF from:

    The 3rd edition is 25% longer, and has been extensively revised. It also contains much new material, as summarized in the highly recommended preface. We are particularly pleased that our very own Measurement Equation, the matrix-based formalism that properly describes a radio telescope in full polarization, has now received pride of place.

    TMS have thoughtfully provided an index to the authors of the many papers that are referenced in the book. It is instructive (and amusing) to see which ASTRON people have made it into this august company, and for what. The champions, in descending order of their number of references, are: Baars(7), de Vos(6), Deller, Hamaker and Weiler(5), van der Tol(4), Boonstra, Bos, Brouw and Smirnov(3), Baan, Bregman, de Bruyn, Hampson, Offringa, Raimond, Spoelstra and van Haarlem(2).

    But most of the Chosen Ones have only one reference: Braun, Brentjens, Fridman, Genee, Harris, Hooghoudt, Ivashina, Kelder, Kokkeler, Millenaar, Noordam, O'Sullivan, Rots, Smolders, van Ardenne, van Capellen, Wieringa, Willis. They are not always mentioned for the work of which they are most proud, but at least they are in there. Any missing ones, for instance of our younger stars, will surely be added in the next edition.


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