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

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    © Bo Thide (Swedish Institute of Space Physics)

    Wireless communications, radio astronomy and other radio science applications are mainly implemented with techniques built on top of the electromagnetic linear momentum (Poynting vector) physical layer. As a supplement and/or alternative to this conventional approach, techniques rooted in the electromagnetic angular momentum physical layer have been advocated and promising results from proof-of-concept radio communication experiments using angular momentum were recently published. This sparingly exploited physical observable describes the rotational (spinning and orbiting) physical properties of the electromagnetic fields and the rotational dynamics of the pertinent charge and current densities. In order to facilitate the exploitation of angular momentum techniques in real- world implementations, we present a systematic, comprehensive theoretical review of the fundamental physical properties of electromagnetic angular momentum observable. Starting from an overview that puts it into its physical context among the other Poincaré invariants of the electromagnetic field, we describe the multi-mode quantized character and other physical properties that sets electromagnetic angular momentum apart from the electromagnetic linear momentum. These properties allow, among other things, a more flexible and efficient utilization of the radio frequency spectrum. Implementation aspects are discussed and illustrated by examples based on analytic and numerical solutions.

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  • 09/02/14--17:00: AstroFest 2014
  • © Astron

    Also this year, we organised the traditional AstroFest, the yearly science day to get an overview of all the wonderful science projects of the astronomy group, the astronomers of the radio observatory RO, and of JIVE.

    This year we went back to Exloo, in the very informal setting of the Diner-Cafe Bussemaker. Erwin de Blok, Zsolt Paragi and Marjan Tibbe took care of the organisation, including the great weather we had that day!

    After the success of last year, all participants were asked to prepare a short, informal presentation, and we would randomly draw (from a magic hat) names of speakers during the day. In this way, we got a very nice overview across the many fields of research we are covering: quite impressive to see all the breadth of what we do!

    We finished off with Jayanne English telling us what to keep in mind when making (convincing) images for public outreach or press releases, a topic that triggered some discussion.

    During the lunch break, many of us went for a visit to the LOFAR core, enjoying the beautiful weather and a lively explanation by Richard Fallows (and his dog).

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    © Astron

    After the success of the "Astronomy Pretty Poster Pageant" (see Daily Image 1/8/2014), another event was organised aimed for improving our skills of producing nice astronomical images (we seem to need this). In the week of Aug 25, we had Dr. Jayanne English visiting ASTRON giving a presentation and hands-on workshops on this topic. Jayanne is an Associate Professor of Physics in the Department of Physics and Astronomy at the University of Manitoba in Winnipeg (Canada). All her career, she has intertwined art and astronomy: she graduated from the Ontario College of Art and Design before moving on to receive her B.Sc. in Astronomy from the University of Toronto, and then her PhD from the Australian National University in 1994.

    As part of her work with NASA's Hubble Space Telescope, she coordinated the Hubble Heritage project ( ) and authored the Hubble Heritage website. She has been also very active during the International Year of Astronomy (2009), producing art work as well as an astronomy image-making video.

    The visit of Jayanne to ASTRON has been fun but also extremely useful. In addition to the workshop, she has worked with some of us to apply her techniques and produce nice images from both WSRT and LOFAR data (some shown in the figure). She has also joined us during the AstroFest in Exloo. Jayanne really enjoyed the visit to LOFAR that we had during the AstroFest but she also gave a short "guest lecture" on the "making of" the pretty - but also explanatory - image of UGC 10288. This image was used for a press release of a paper involving also our George Heald (and posted also as our Daily Image of November 15 last year ).

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    © ASTRON

    On June 25 and 26, seventeen design experts from Transfer DSW, Sintecs, Strukton, ASTRON and IBM came together at the Hanze Institute of Technology (HIT) in Assen to discuss and learn about the newest printed circuit board (PCB) technologies presented by Optiprint and IBM Italy.

    The parties present at the workshop are closely involved in designing the microserver printed circuit board. They received information about the newest technologies in PCB design, rigid and flexible printed circuit boards as well as application areas and constraints. This led to vivid discussion concerning design approaches and constraints, for example how much data can be transported over the flexible connections between rigid and flexible parts of such electronic circuit boards.

    This particular seminar was a semi-closed Users Platform event. Future technology seminars organized by the Exascale Centre can be either closed or open, depending on the topic. Thanks to the Hanze Institute of Technology for hosting us.

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  • 09/08/14--17:00: To Save the Rhinos
  • © Madroon Community Consultants (MCC)

    Last week, a multi-disciplinary group from various Dutch institutes met with South African counterparts to discuss what the Netherlands might contribute to saving the rhinos. The workshop was hosted by the Southern African Wildlife College (SAWC) in Hoedspruit, on the edge of the Kruger Park. The Dutch delegation was led by Dr Louis Verdegaal, a Director of the Netherlands Organisation for Scientific Research (NWO).

    The past six years have seen an alarming increase in the poaching of Rhinos for their horns, which are highly valued in some East Asian countries for their (imaginary) medicinal and magical powers. The only real solution would be the elimination of this market, which is easier said than done. In the meantime, the poachers have to be resisted as much as possible.

    First of all, the reporting of incidents by rangers can be greatly improved by means of technology like smartphone apps that instantly report images and position information back to base. In addition, it should be possible to make the "smart fence" around the park even smarter, to give timely and accurate warnings of poacher incursions. And finally, the Netherlands Forensic Institute (NFI) can help with the judicial prosecution of poachers.

    ASTRON and the South African SKA project are involved because of their expertise in image processing, e.g. for reconnaissance from above. We might also play a role in combining large amounts of surveillance data, and their compact presentation to the enforcers in the field.

    The image shows the tagging of a rhino that has been drugged by means of a dart fired from a helicopter, and the implantation of a tracing chip in its precious horn. When seeing and touching these mighty beasts, it is impossible not to feel distressed about their plight.

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    © ASTRON

    Neutral hydrogen (HI) absorption studies provide great insights in how Active Galactic Nuclei work. Neutral hydrogen has been detected in the inner regions of several radio galaxies, suggesting that the HI gas and the radio plasma may be interacting. Especially compact radio sources, which are likely to be young AGN, appear to be often embedded in an HI-rich medium. The HI appears to be unsettled, suggesting that it may be inflowing or outflowing, and regulating the fueling of the AGN. The detailed analysis of the HI in compact radio sources is necessary to understand the physical mechanisms which may may turn a dormant AGN in a radio loud object.

    We have done this using observations with the Australia Telescope Compact Array (ATCA) of the young (

    The asymmetries at the edges of the disk can be used to date the last interaction of PKS B1718-649 with a companion to more than 1 Gyr ago. The tilted-ring model of the HI disk shows that this event may have formed the disk as we see it now, but that it is not responsible for triggering the AGN.

    In absorption, we detect two separate lines (Fig. 2). A link between these clouds and the radio activity is quite possible. The most likely possibility is that the absorption components come from two small clouds that are not part of the regularly rotating disk(Fig. 3). They may belong to a larger population present within the galaxy and which may contribute to fueling the AGN. Simulations of the accretion proces into the AGN, show that cold clouds and filaments may be forming from condensation of the hot halo. These clouds would chaotically collide with the surrounding medium, loosing angular momentum, falling toward the center of the galaxy and triggering the AGN acticity.

    These results have been presented in an A&A paper, now in press, by F. M. Maccagni, R. Morganti, T.A Oosterloo, E. K Mahony:

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    © LWA

    Construction of the first station of the Long Wavelength Array (LWA1)was completed in 2011. The LWA1 has since undergone commissioning and regular scientific observations from four calls for proposals with a second station funded and currently under construction at Sevilleta wildlife refuge near Socorro. The LWA1 is co-located with the Very Large Array and consists of 262 dual-polarization dipoles, with four independently-steerable dual-polarization beams available that can be tuned to any frequency between 5 and 88 MHz. I am going to present a brief overview of the station architecture and the larger vision for the Long Wavelength Array project. I will also discuss a selection of the first scientific results obtained with LWA1. This includes transient searches with the discovery of radio emission from fireballs, detection of pulsars, including millisecond pulsars, giant pulses, and RRATs, Solar and Jupiter bursts, ionospheric science, and imaging of lightning. In the context of LWA1 and beyond I will briefly discuss progress made towards the detection of the cosmological dark age with LWA1 and a newly-constructed station at the Owens Valley Radio Observatory in California. This includes an overview for the path forward with the larger LWA project in the coming years toward a general purpose imaging instrument for arcsecond-scale structures below 100 MHz and a super station for transient searches and cosmology.

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    © C. Sobey on behalf of the LOFAR collaboration; no connection with Joy Division, Peter Saville, et al.

    The poster above won 3rd prize in the Astronomy Pretty Poster Pageant (APPP) 2014. All entries are available for editing and outreach purposes within ASTRON.

    The average pulse profile shapes of radio pulsars are remarkably stable when summed over at least a few hundred rotations. This reflects their clock-like rotational predictability, and enables their use as precision physical probes, for example, towards testing theories of gravity.

    Nonetheless, pulsar emission variability has been recognised on almost all timescales that are observationally accessible: from nano-second 'shots', expected to be the quanta of pulsar emission; to multidecadal variations, presumably due to evolution of the magnetic field.

    PSR B0823+26 displays a plethora of magnetospheric emission characteristics over a wide range of timescales. Low radio-frequency, single-pulse observations obtained using LOFAR (the Low-Frequency Array telescope) provided us with a fresh look at this pulsar. This allowed us to identify a sporadic and weakly-emitting 'quiet' mode over hour-long periods, which displays rotating radio transient-like features and a nulling fraction forty-times greater than that during the more regularly-emitting 'bright' mode. Furthermore, the transition from the newly-discovered 'quiet' mode (the lower three nulls from the bottom of the image) to the 'bright' mode (the rest of the pulses in the image) occurs within one rotational period of the pulsar (0.5 s), and is concurrent across a broad range of radio frequencies.

    Studying pulsars like PSR B0823+26 (including PSR B0943+10 - another interesting mode changing pulsar - see here and here for previous daily images) furthers our insight into the relationship between the host of magnetospheric radio emission characteristics and what they might teach us about the elusive magnetospheric radio emission mechanism. The paper describing these and further results has been submitted.

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    © ASTRON

    September 13 marked the end of a 2-year project, and the beginning of a new one.

    In close cooperation with CAMRAS, Anke den Duyn launched the youth novel "Het Logboek" by handing the first copies to Anne Margreet Muller, daughter of Lex Muller, one of the first directors of ASTRON. And to Marc Oort, grandson of Jan Oort, founder of Dutch radio astronomy.

    Today, the author will sign copies of the book for ASTRON and JIVE employees.

    ASTRON has asked Anke to write Het Logboek. It is a breathtaking adventure against the background of the Dwingelderveld, with an important role for the 25m Dwingeloo Radio Telescope. The story is based on the input gathered from a large number of (former) ASTRON employees and others, and the creative talents of Anke.

    The launch of the book marks the kick-off of a new adventure: "Kijk eens wat verder dan de sterren" (Just look beyond the stars). This is a project in which primary schools are challenged to embark their pupils on a journey to radio astronomy, and by doing so to arouse their interest in science and technology.

    We are eagerly awaiting what the future will bring..

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    © Astron

    The spiral galaxy M101 belongs to a small and select group of galaxies that are the HI icons of the WSRT. M101 is one of the largest nearby late-type galaxies and, because it is seen fairly face-on, offers one of the most detailed views of the complex structure and kinematics of spiral galaxies. Because of this, it was one of the first galaxies observed with the WSRT in the 21-cm line of atomic hydrogen (Allen, Goss & van Woerden 1973) and over the years, every time the performance of the WSRT improved, the galaxy has been observed again (now five times in total).

    The latest observations were done last year. Twenty days of observation were used to cover the entire extent of the galaxy (about 1 degree). Compared to the observations of the early 70's, the new data reveal features that are about hundred times fainter than the weakest HI clouds in the first observations. The main aim of the observations is to study, in the greatest possible detail, the effects of star formation and of gas accretion on the disk of a spiral galaxy. For this purpose, these HI data will be combined with WSRT and LOFAR observations of the (polarised) continuum emission of M101 (also involving George Heald and Sarrvesh Sridhar).

    The blue (but less beautiful) version of the poster above won 1st prize in the Astronomy Pretty Poster Pageant (APPP) 2014. This poster I was able to make thanks to the lessons of Jayanne English, who visited ASTRON recently

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  • 09/13/14--17:00: Het Logboek
  • © ASTRON

    This weekend, the youth novel "Het logboek" will be presented to Marc Oort, grandson of Prof. Jan Oort, the founder of radio astronomy in the Netherlands, and to Anne Margreet Muller, daughter of Lex Muller, radio engineer and the first director of ASTRON. "Het logboek", commissioned by ASTRON, is a compelling adventure set in the moorlands of Dwingeloo with the glorious telescope in the background.

    Luna and her friends are confronted with mysterious events when camping in the forest around Lhee. Fences disappear, game computer GPUs get stolen, remarkable characters cross the forest... Will they be able to unravel the secret?

    The adventure novel "Het logboek" is also a journey through Dutch astronomy, featuring prof. Jan Oort and prof. Lex Muller, the Wurzburg telescope were it all began, and related historical events in 70 years of radio astronomy in the Netherlands.

    At the presentation of the book, schools from villages with a connection to ASTRON will be present as well. Children from Diever, Beilen and Borger-Odoorn will get a first copy of the book. Will they pick up the excitement of science and technology?

    More information:

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  • 09/16/14--17:00: LOFAR Imaging Busy Week XXI

    In some societies, you're not really an adult until you reach 21. By that reckoning LOFAR imaging is now all grown up!

    The twenty-first installment of LOFAR's successful series of Imaging Busy Weeks took place during the first week of September 2014 at ASTRON. The focus of this busy week was the developments being made by the Calibration and Imaging Tiger Team (CITT). Enhancements are being made by the CITT to the Standard Imaging Pipeline, in order to quickly and robustly produce science-grade images from LOFAR interferometric observations. These enhancements are still in development and require expert testing to ensure that they are up to scratch! For that reason the CITT is working closely with a broad range of scientists within the collaboration.

    Highlights of the busy week included: testing of our fast calibration routine (based on "Stefcal") that offers a vast improvement in runtime and memory usage; imaging with the new and more capable LOFAR awimager; testing the CITT automated self-calibration pipeline; and testing of determination and application of ionospheric phase screens to LBA and HBA imaging data. We also experimented with some of the tools developed by the EoR group (for example, producing movies like this one), heard an exciting update on the "extreme peeling" strategy employed by Reinout van Weeren, and took steps toward making that sophisticated scheme available to other users.

    Today's image shows some candid photos of the Busy Week team hard at work. The background is a high resolution (5"), deep (~500 μJy/beam), broad bandwidth (55 MHz) image produced using data calibrated by the CITT selfcal pipeline (see this image from the archives). It demonstrates that deep, wide field of view and broad bandwidth imaging is within our grasp � and that there is still more progress to be made in the pipeline to implement direction dependent calibration and imaging! These developments will be the focus of future busy weeks.

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    © Jimi Green

    I will outline recent work on Zeeman splitting of Galactic hydroxyl masers, both ground and excited-state transitions, discussing the expectations and conventions of magnetic fields determined from the spectral line splitting. I will discuss a large scale survey for ground-state hydroxyl towards regions of high mass star formation and a smaller scale survey of excited-state hydroxyl exploring the propensity of linearly polarised pi components (previously believed to be elusive). Finally I will talk about the Square Kilometre Array, it's status and progress, and what areas of this work it may contribute to.

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    © Sally Cooper / PWG

    LOTAAS is the LOFAR Tied-Array All-Sky Survey, an ongoing LOFAR all-northern-sky survey for pulsars and fast transients - i.e. anything that emits millisecond timescale dispersed bursts. Using only the Superterp HBA stations, each pointing is comprised of three sub-array pointings and within the field of view of each incoherent beam we also form 61 tied-array beams. We also generate an additional 12 tied-array beams to point at known sources giving a total sum of 222 beams per survey pointing. In other words, this is a pulsar and fast transient survey approach unlike any other and a unique stepping stone on the path to surveying with SKA-Low. With a bandwidth of 32 MHz, a spectral resolution of 12 kHz, and a sampling time of 492 microsec, LOTAAS generates data at an astounding rate of 35 Gbps (close to the total possible system throughput of the LOFAR CEP2 network). Each 1-hour pointing produces 16 TB of raw data.

    LOTAAS has been observing since December 2012, and we have processed 160 pointings on the Dutch supercomputer Cartesius (operated by SURFsara). Using Fourier-based pulsar searching methods we have produced more than 3 million pulsar candidates. A machine learning classifier is then applied to the candidates and the most promising go forward for human inspection. LOTAAS has so far discovered 8 new pulsars. These are marked with large red stars in the above figure, which also shows the current observed sky coverage in green. Along with LOFAR's first two pulsar discoveries in the commissioning survey LOTAS, which are marked with orange stars above (Coenen et al. 2014), LOFAR now has a total of 10 pulsar discoveries. The LOTAAS survey has also redetected 80 known pulsars including 4 independent discoveries of pulsars originally discovered by the Green Bank North Celestial Cap Survey. The survey is only one third of the way through its first pass (of three) of the sky, with many more pulsars waiting to be discovered. We are also sifting through the already processed data to find intermittent pulsars, and single dispersed bursts.

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    Twice a year, representatives of the Dome team come together to share knowledge and discuss progress on a face-to-face basis. This year's second meeting was held September 16-18th at the IBM Research Laboratories in Zurich (ZRL). Present were 35 colleagues from ASTRON, IBM Netherlands at ASTRON, IBM ZRL and SKA South Africa.

    Dome and SKA

    Among other things, the group discussed the mapping of Dome work onto SKA design work. A preliminary design review (PDR) is planned early next year. The discussion also covered ways of contributing to the SKA beyond PDR. There was also an exchange of thoughts on fundamental aspects, such as the extent to which the physical bulk of SKA data should be kept close to the telescope or at regional science data centres.

    Progress and more progress

    Researchers from various work streams were happy to report significant progress. For instance, there is now a concept-design of an extremely power-efficient chip for the low-frequency aperture array (LFAA) systems. It will be included as an alternative design in the PDR documentation set. Two work streams, Novel Algorithms and Real-time Communication, have started only recently. Nevertheless, researchers were able to share some initial results, and plans for the near future. Another great example is the microserver. It is now ready for ASTRON and SKA South Africa to start implementing and testing software on it (think correlator and imaging algorithms).

    The next face-to-face meeting is planned for March 2015. The picture shows the members of the Dome team in front of one of the ZRL buildings just before the final session. Inset left: Erik Vermij explaining his award-winning accelerator research. Inset right: Yan Grange reporting progress on access patterns (storage).

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    At the end of summer, when the nights are getting longer and darker, the constellation of Cygnus, with all its beautiful emission nebulae, is visible high above our heads. An ideal target for testing a new astrographic telescope, designed and built by Rik ter Horst. It's a unique design, a corrected Schmidt-Newtonian with a 300mm mirror and a fully corrected field of almost 4 degrees. The photographical speed is F/2.5, so you can really make "snapshots" with the attached (H-alpha modified) Canon 5D MKII, a digital single-lens reflex camera with a full frame 24x36mm sensor.

    Adjusting such a fast optical system is not easy, the depth of field at focus is only 17 micron, so the tilt of the imaging sensor has to be precisely adjusted to get sharp star images across the entire field.

    The image above is a mosaic made from two completely different integrations. The left part was exposed for 15 x 60 seconds at 1600ISO, the right part 12 x 300seconds at 400ISO, as a result the latter has much less noise. A mosaic was made using PixInsight software, and it did a very good job equalizing both sides of the image and putting them together seamlessly. The result is a 34 Megapixel image that shows the North America nebula (NGC7000) and to its right the Pelican nebula (IC5070 and IC5067) Flat, dark and bias frames were used for image calibration.

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    © Astron/DESP

    After the recent delivery of an Uniboard processing rack to Cambridge, the first antenna measurement results are now presented. This measurement campaign was a collaboration of the Astrophysics group of Cambridge University, INAF, Politecnico di Torino (Italy) and ASTRON.

    As shown in the pictures, the setup consists of an array of 16 dual polarized antennas, 2 receiver racks and 1 UniRack with 4 ADUs (Analog to Digital converter Unit), and 2 Uniboards.

    A hexacopter was used to create an artificial radio source above the array. It flew 100-150 m above the antenna field, with a speed of 3-4 m/s along a GPS-controlled path. It made several 10-minute flights, carrying a RF source transmitting on different frequencies in the range of 50-450 MHz. One of the photos shows it carrying a dipole antenna for a 50 MHz test.

    The output signals of the array antannas were captured from the Uniboards using the modified EMBRACE Capture software. The Uniboards are in full control with the Uniserver software.

    The plot shows a first result of the 50 MHz flight, in which the hexacopter flew several times through zenith. It shows the signal power of the Y polarization from the 16 antennas and the blue line is the sum of all 16 antennas.

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    © R. Jay GaBany

    In today's colloquium I will explain how resolved stellar populations in the nearby Local Group dwarf galaxies have been used to study the detailed chemical, kinematic and star formation history of these nearby small systems. I will focus on the results from the DART (Dwarf Abundances and Radial velocities Team) surveys and also some recent work combining spectroscopy with colour-magnitude diagram analysis to measure the time scale for chemical evolution.

    The picture shows an edge-on, warped spiral galaxy, NGC 59007, and an extended stellar tidal stream, created through gravitational interaction.

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  • 09/25/14--17:00: ASTERICS!
  • © ASTRON

    Earlier this month, a large proposal named ASTERICS (Astronomy ESFRI & Research Infrastructure Cluster) was submitted to the Horizon 2020 Call - INFRADEV-4. ASTERICS aims to bring together all the astronomy facilities currently included in the ESFRI (European Strategy Forum on Research Infrastructures) list of opportunities - this includes the SKA, CTA, E-ELT and KM3Net. The various pathfinder facilities (including LOFAR and e-VLBI) are also involved. The image above shows the main partners involved in the project.

    The main thrust of the proposal is to typical problems that are common to all of these facilities, in particular the Big Data challenge faced by these facilities and the ambition to properly interface their various data products with the Virtual Observatory. In addition, there are several interesting common technical projects, in particular the synchronisation of time and frequency across distributed arrays. Another interesting feature of ASTERICS is the ambition to open-up the data generated by the ESFRI related astronomy facilities to the general public with a strong commitment to the principles of the recent Science 2.0 initiative and the anticipated development of several citizen scientist applications. The PIs of the major work packages are Giovanni Lamanna (LAPP, Paris), Francoise Genova (CDS, Strasbourg), Huib Jan van Langevelde (JIVE, Dwingeloo) and Stephen Serjeant (Open University, UK).

    ASTRON coordinated the submission of the ASTERICS proposal with major contributions from Gert Kruitoff, Rob van der Meer, Emmy Boerma, Andre van Es, Marco de Vos & Anneke Steenbergen.

    The proposal is expected to be evaluated over the next few months. The Call is known to be heavily over-subscribed but hopefully it will be well received by the independent review panels. Fingers crossed... !

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    © Onsala Space Observatory/L. Wennerback (aerial picture) and Magnus Thomasson (owl)

    During my recent visit to Onsala Space Observatory, the replacement of the old radome around the 20m telescope ( was in full swing. Organized by OSO's former director Hans Olofsson, the operation comprises replacing the top segment first, after which each of the other, lower sections will be individually replaced. It is expected that the transmittance and homogeneity of the radome will be much improved and that all work will be finished before the Swedish winter sets in.

    As to that, the work appears to be overseen by the wisdom of an eagle-eyed eagle-owl (or Oehoe in the Netherlands, see (*) below) shown here in a magnificent picture by Magnus Thomasson. Alternatively, it might be wondering whether this egg will hatch into anything edible.

    By the way, note the Swedish LOFAR station which is clearly visible in the background.

    (*) From WIKIPEDIA: The Eurasian eagle-owl (Bubo bubo) is a species of eagle-owl resident in much of Eurasia. It is sometimes called the European eagle-owl and is, in Europe, where it is the only member of its genus besides the snowy owl (B. scandiacus), occasionally abbreviated to just eagle-owl. The Eurasian eagle-owl has a wingspan of 160-188 cm, with the largest specimens attaining 200 cm . The total length of the species can range from 56 to 75 cm. Females weigh 1.75-4.2 kg and males weigh 1.53 kg.

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