Endorsement that money can't buy

August 6, 2015, 5:00 pm

≫ Next: First ever on-site assembled LOFAR High Band Antenna touched down in Baldy, Poland

≪ Previous: Quad-mode antenna for sparse L-band tiles

Recently it was announced that President Obama (see picture) has signed an executive order calling for the US to build the world's fastest computer by 2025(*). After listing the mind-bogglingly huge numbers that usually describe the performance of such a machine, the BBC report went on:

Efforts to construct an exascale computer are not entirely new. Recently, IBM, the Netherlands Institute for Radio Astronomy (ASTRON) and the University of Groningen announced plans to build one to analyse data from the Square Kilometre Array (SKA) radio telescope project.

It is not clear whether these are Obama's words or just the BBC reporter's, but this is the kind of endorsement that money can't buy.

(*) Presently the fastest computer in the world is Chinese, and also Saudi Arabia has a fast one.

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First ever on-site assembled LOFAR High Band Antenna touched down in Baldy, Poland

August 9, 2015, 5:00 pm

≫ Next: Cool and warm gas in nearby galaxies

≪ Previous: Endorsement that money can't buy

The first of three Polish LOFAR stations will be located in Baldy, Poland. It belongs to the University of Warmia and Mazury - UWM - in Olsztyn. The construction of this new station of the International LOFAR Telescope is now nearing completion. All the groundwork, like installing a drainage system, and geodetic position determination for the antennas, have been carried out by SKANSKA Company under supervision of UWM. On behalf of AstroTec, Han Wessels and Zabet Ahmadi provided assistance with the HBA assembly and roll-out.

For the first time in the history of LOFAR, all High Band Antennas (HBA) were assembled on-site, and not in a factory. It was a truly titanic labour, done mainly by volunteer students of UWM. The reason for this approach was to save on the substantial cost of transporting the rather bulky HBAs, by shipping their components in the most compact way.

The team had to cope with severe conditions: thunderstorms hammered the specially equipped tent and nearly flooded the freshly dug cable trenches, and last week the temperatures soared to more than 35 degrees C. Not many people realise that to assemble 96 HBA tiles, where each tile actually consists of 16 dual polarized antennas, no less than 14.000(!) components are involved. We may consider it as a real achievement that the team kept the spirit alive.

The center photo shows the team. Top row, from left: Bartosz Dabrowski (UWM), Andrzej Krankowski(UWM) and Han Wessels (AstroTec). Bottom row: Jacek Kapcia (UWM), staff and students (the volunteers) from UWM: Katarzyna, Tomasz, Kacper, Ewa, Adam, lukasz, Zabet Ahmadi (AstroTec), Andrzej Malon (UWM).

You may check the LOFAR POLSKA Facebook page to see the current status of the roll-out. A video showing the touchdown of the very first assembled HBA can be seen here . We expect to have the Baldy station commissioned before the end of August. Another two Polish LOFAR stations near Borowiec en Lazy are under construction also. Watch this space.

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Cool and warm gas in nearby galaxies

August 10, 2015, 5:00 pm

≫ Next: Building Bridges (pun intended)

≪ Previous: First ever on-site assembled LOFAR High Band Antenna touched down in Baldy, Poland

Young stars produce a lot of energy and heat the gas that surrounds them. We can see this in galaxies as an increase in the velocity dispersion (random motions) in the gas (observed as neutral hydrogen with radio telescopes). However, for stars to form the gas must be cool enough for gravity to overcome these random motions so that it can collapse. For stars to form we therefore need gas with a low velocity dispersion.

We can see these effects directly in radio observations of the gas in galaxies. The colour picture shows an image of the neutral hydrogen (in cyan) of dwarf galaxy Holmberg II that was observed with the Very Large Array in the US as part of the THINGS survey. The purple shows the locations of young stars in this galaxy using ultra-violet data obtained with the GALEX space observatory.

By summing together many of the neutral hydrogen spectra in these radio data, we can obtain a very high signal-to-noise spectrum that shows the amount of gas with respect to the local rotation velocity. This spectrum is shown in red in the top-left panel. The profile can be decomposed into two components, one narrow, low-velocity dispersion component (dotted profile, representing cool gas) and one broad, high-velocity dispersion component (dashed profile, representing warm gas). In the bottom part of that panel the difference between the component fits and the data is shown. It is clear that two components are a good representation of the data.

We can measure the profiles at many radii in this galaxy, and determine the velocity dispersion of the total profile, as well as the broad and narrow components. These dispersion values are shown in the bottom-left panel. The total profile is shown as gray squares, the broad component as filled circles and the narrow component as open diamonds. Both the narrow and broad dispersions are lower in the outer parts of the galaxy, probably due to the smaller input from (for example) young stars (the colour picture shows very few young stars in the outer parts).

The total dispersion remains constant as a function of radius though. This is due to the changing balance between the amounts of cool and warm gas from the inner to the outer parts of a galaxy. In the inner parts the amount of cool gas is much higher, so the low-velocity dispersion gas keeps the total velocity dispersion low. In the outer parts there is very little cool gas, so the total velocity dispersion is dominated by that of the warm gas. The fact that the balance is such that the total dispersion remains approximately constant is an important boundary condition for theories of star formation.

This work was done by (then) PhD student Roger Ianjamasimanana from South Africa, with (amongst others) ASTRON scientists Erwin de Blok and George Heald. This work was recently published in the Astronomical Journal (AJ, 150, 47) and can also be found at http://arxiv.org/abs/1506.04156

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Building Bridges (pun intended)

August 11, 2015, 5:00 pm

≫ Next: ASTRON/JIVE Nearest Neighbours

≪ Previous: Cool and warm gas in nearby galaxies

As pointed out in a highly stimulating recent book(*), human beings bond and cooperate with the help of shared myths and arcane rituals. And whereas the myths are necessarily rather uniform, the rituals can vary from place to place. In Dwingeloo they take the form of teaching visitors to play bridge. The image shows a recent batch from Zuid Afrika, who arrived under explicit instructions from their bosses back home to subject themselves to this ordeal(**). From left to right:

Kshitij Thorat (thorat.k@gmail.com)

Modhurita Mitra (modhurita@gmail.com)

(The venerated teacher of generations of visitors)

David Prinsloo (dprinsloo@sun.ac.za)

Marcellin Atemkeng (marcellin.atemkeng@yahoo.fr)

We greatly value our strong ties with ZA. David Prinsloo is from the stable of David Davidson in Stellenbosch. He has left us by now, but not before sparking a spirited debate about alternative solutions for Mid-Frequency Aperture Arrays (MFAA) for SKA. The other three are members of the lively 3rd Generation Calibration (3GC) and Imaging group around Oleg Smirnov at Rhodes University and Cape Town. They are here to be let into the secrets of LOFAR data reduction by Tammo Jan Dijkema. Perhaps they will turn out to be harbingers of the return of MeqTrees, which sadly disappeared from Dwingeloo(***) a few years ago.

(*) "Sapiens: A Brief History of Humankind", by Yuval Noah Harari.

(**) As usual, they were relieved to find that it actually was fun, especially after 22:30.

(***) The phrase is a none-too-subtle reference to a Dutch book with the title "How God disappeared from Jorwerd", the latter being a small town in Friesland.

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ASTRON/JIVE Nearest Neighbours

August 12, 2015, 5:00 pm

≫ Next: Large Prototype of a Dual-Polarized Dense Dipole Array Manufactured

≪ Previous: Building Bridges (pun intended)

Just a photograph taken from my office(!) of our nearest neighbour showing up with kids.

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Large Prototype of a Dual-Polarized Dense Dipole Array Manufactured

August 13, 2015, 5:00 pm

≫ Next: Muddy Feet (but not of Clay)

≪ Previous: ASTRON/JIVE Nearest Neighbours

In a dipole array backed by a ground plane there exists an inductance effect which is mostly introduced by the ground plane and, to a lesser extent, by the element itself. This inductance can be compensated for by inserting a series capacitance between the tips of neighbouring elements. The result of this compensation will be a near-constant current along the elements of the array which will imitate the infinite current sheet array introduced by Wheeler. The series capacitances between the tips of neighbouring elements mentioned above can either be realised by inserting physical capacitors or by increasing the inherent capacitance present between neighbouring elements by careful placement of the array elements.

This square meter DDA prototype consists of a 10x10x2 array of densely packed printed dipoles above a ground plane. Array elements are connected in parallel-pairs and fed differentially through a common-mode suppressing feed-board.

The work forms part of the PhD work of Jacki Gilmore from Stellenbosch University in collaboration with ASTRON through MIDPREP. The PCB manufacturing was done in-house by Albert van Duin and the mechanical design and manufacturing was done by Sjouke Kuindersma. The measurements will be done at Stellenbosch University in the near future.

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Muddy Feet (but not of Clay)

August 16, 2015, 5:00 pm

≫ Next: A fast molecular outflow as seen by ALMA

≪ Previous: Large Prototype of a Dual-Polarized Dense Dipole Array Manufactured

Under the traditional command of Dr Bob, the ASTRON/JIVE summer students have once again braved the frigid temperatures and crab-infested mud-flats of the Wadden Sea to trek to Ameland...

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A fast molecular outflow as seen by ALMA

August 17, 2015, 5:00 pm

≫ Next: Annual ASTRON JIVE softball match

≪ Previous: Muddy Feet (but not of Clay)

It is now well established that cold gas can be expelled from galaxies at high velocities. This is an important observation because cold gas is what is needed to form new stars. Expelling the gas means reducing, or even stopping, the process of star formation with important consequences for the evolution of the host galaxy.

One possible mechanism is that the cold gas gets blown out of a galaxy via the interaction with the fast radio jets coming from the Super-Massive Black Hole in the galaxy centre. This is still a poorly understood process because the details of it are very difficult to observe directly. The situation has now very much improved through ALMA observations of the radio-loud, Seyfert 2 galaxy IC5063, an old friend of ours and a regular guest of the Astron/Jive Daily Images (1-3-2013 and 22-10-2007).

We have used high-resolution (0.5 arcsec) CO(2-1) observations performed with ALMA to trace the kinematics of the molecular gas in this galaxy. From earlier observations, IC 5063 was known to have a fast outflow of cold gas driven by the radio jets in this galaxy, but due to the low spatial resolution of these data, it was not possible to study it in detail. The new ALMA data have much better resolution and allow to image, for the first time, in detail a massive, fast outflow - with velocities up to 650 km/s - of cold molecular gas.

Although, as expected, the highest outflow velocities are seen at the location where the radio jet directly hits a large gas cloud (about 0.5 kpc from the nucleus), the exiting result is that the outflow of molecular gas actually extends along the entire radio jet (see the position-velocity plot in the figure above). It is the first time that the process of a plasma jet interacting with the surrounding medium can be followed in such a detail.

All the observed characteristics can be described by a scenario of a radio plasma jet expanding into a clumpy gaseous medium, interacting directly with the clouds while also inflating a cocoon of gas that drives a lateral outflow into the interstellar medium. Interestingly, this model is consistent with results obtained by recent numerical simulations so it looks like things are starting to make sense.

The detailed description of the results can be found in a paper published in Astronomy & Astrophysics "The fast molecular outflow in the Seyfert galaxy IC~5063 as seen by ALMA" by Raffaella Morganti, Tom Oosterloo, Raimond Oonk, Wilfred Frieswijk and Clive Tadhunter. Click http://arxiv.org/abs/1505.07190 for the full paper

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Annual ASTRON JIVE softball match

August 18, 2015, 5:00 pm

≫ Next: SKA Board meeting No. 18

≪ Previous: A fast molecular outflow as seen by ALMA

The annual softball match under the leadership of Bob Campbell is one of the sporting highlights of the summer-student season, and this year's edition was made all the more sprightly by an especially youthful set of guests from the Janssen and Colomer families.

The final score will be lost to history since no one actually seemed to be counting, but the astroturf was green and the sun was shining and a good time was had by all.

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SKA Board meeting No. 18

August 19, 2015, 5:00 pm

≫ Next: ASTRON News Summer 2015 edition

≪ Previous: Annual ASTRON JIVE softball match

The SKA Board met in South Africa last month but with the help of some chartered flights they were also able to fit in a visit to the SKA site in the Karoo desert and then a school in Carnarvon. The images show the impressive progress being made on all fronts: telescopes and schools included. This was also the last meeting of Jan van der Donk (Ministry OCW) before his well-deserved retirement.

At ASTRON, lunchtime today, Michiel van Haarlem will review the actions arising from the Board meeting and the various other issues that were discussed.

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ASTRON News Summer 2015 edition

August 20, 2015, 5:00 pm

≫ Next: LOFAR Radio telescope now has more than 100.000 dipole antennas!

≪ Previous: SKA Board meeting No. 18

The Summer 2015 edition of ASTRON News is now available!

2015 has been a very successful year so far and we have many interesting articles waiting for you inside this issue of the ASTRON News.

Our researchers have continued to make new scientific discoveries with LOFAR and the Westerbork Synthesis Radio Telescope (WSRT); we will update you with the latest results from the Astronomy Group.

Another big update comes from APERTIF. Following the successful Critical Design Review in October last year, the upgrade of the first six dishes of the WSRT to the new APERTIF system is now in full swing. Also, the LOFAR Calibration & Imaging Tiger Team are working hard on the much needed enhancements to the LOFAR calibration and imaging software.

In March, our building was officially opened by State Secretary, Sander Dekker. This day was full of festive activities that you can read about.

Another important event in Dwingeloo was the inauguration of JIVE as an ERIC. Robert-Jan Smits, Head of the Directorate General for Research and Innovation of the European Council, handed over a plaque recognising the excellence of JIVE as a research infrastructure provider.

We wish everybody a great summer and have fun reading this issue of the ASTRON News.

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LOFAR Radio telescope now has more than 100.000 dipole antennas!

August 23, 2015, 5:00 pm

≫ Next: Children used the LOFAR telescope to generate their first astronomical image.

≪ Previous: ASTRON News Summer 2015 edition

Friday August 21th, the recently built LOFAR station at Baldy in Poland, was opened officially by Prof. Ryszard Górecki, Rector of the University of Warmia and Mazury in Olsztyn.

In the week before, a Site Acceptance Test was performed successfully by ASTRON system engineers Menno Norden, Henri Meulman and Klaas Stuurwold, and witnessed by representatives from the new owner of the station, the University of Warmia and Mazury. Completing the Site Acceptance Test qualifies the station to serve as an international LOFAR station, and simultaneousny sets a new record: more than 100.000 dipole antennas are now incorporated in this radio telescope!

LOFAR , the LOw-Frequency ARray, is a radio interferometer constructed in the north of the Netherlands and has stations across Europe. Utilizing a novel phased-array of simple omni-directional antennas instead of mechanical beam forming with a dish antenna, LOFAR covers the largely unexplored low-frequency range from 10-240 MHz and provides a number of unique observing capabilities.

The new station at Baldy is currently the easternmost component of LOFAR, and Prof. Andrzej Krankowski of the University of Warmia and Mazuria in Olsztyn will work with other centers on research into pulsars, the distribution of neutral hydrogen in the early universe, and a search for radio emissions from planets. He will also take part in programs involving global navigation and local environment research.

For more information, please watch this report from TVP (Polish Television) about this new LOFAR station. Another two Polish stations are under construction as part from the POLFAR consortium.

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Children used the LOFAR telescope to generate their first astronomical image.

August 24, 2015, 5:00 pm

≫ Next: Dreamy but not Dreaming

≪ Previous: LOFAR Radio telescope now has more than 100.000 dipole antennas!

On 7-15 August, the 25th Astronomy festival took place at Fleurence (France). Part of the festival was the 10th Astrojeunes festival for young people between 3 and 18 years old.

Since two years, Astron is a partner in this event. This year, the LOFAR ovservatory provided time and facilities to allow children up to 12 years old to generate their first astronomical image. After observing NGC6251 on wednesday morning, the children processed the data themselves in the afternoon. Each received a certificate to remember this event (see picture).

The experience was a great success. The children were very enthousiatic to discover the actual duties of an astronomer. In addition, the discovery of using Linux was also very new to them.

Astrojeunes would like to thank ASTRON and the LOFAR observatory again for their support and gifts to the children.

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Dreamy but not Dreaming

August 25, 2015, 5:00 pm

≫ Next: Dreamy but not Dreaming

≪ Previous: Children used the LOFAR telescope to generate their first astronomical image.

Once, the 25m Dwingeloo Radio Telescope was the biggest in the world, playing a major part in the grand adventure of unlocking the Multiverse at radio wavelengths. Now it is a National Monument, while its pioneering role has been shouldered by the Westerbork Telescope and LOFAR(*).

However, it is not put to pasture to dream about the glorious past, as this picture seems to suggest. The fires are still burning, but now in the service of popular outreach, and some quite sophisticated amateur radio astronomy by CAMRAS.

But sometimes a picture is just right. Enjoy.

(*) and a few other radio telescopes elsewhere in the world.

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Dreamy but not Dreaming

August 26, 2015, 5:00 pm

≫ Next: The Zoo of Accreting Compact Objects

≪ Previous: Dreamy but not Dreaming

But sometimes a picture is just right. Enjoy.

(*) and a few other radio telescopes elsewhere in the world.

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The Zoo of Accreting Compact Objects

August 27, 2015, 5:00 pm

≫ Next: The Art of making name badges

≪ Previous: Dreamy but not Dreaming

From August 3 - 7, 2015, we hosted a workshop entitled "The Zoo of Accreting Compact Objects" at the Lorentz Center in Leiden.

This workshop was inspired by the recent discovery of a class of transitional millisecond pulsars, which are systems that switch between states as a rotation-powered radio pulsar and an accreting X-ray binary. The ASTRON/UvA pulsar group has played a large role in the discovery and multi-wavelength characterization of such systems, which we believe provide excellent laboratories for studying accretion physics. As such, we invited a select group of world experts on other types of accreting compact objects in the hopes of spurring new collaborations and establishing new observational/theoretical research lines.

The workshop was very rewarding, and the informal format of the Lorentz Center promoted lots of interaction and discussion sessions. It was also fun writing on the tables and walls.

This workshop was funded by ERC Starting Grant number 337062 (DRAGNET) to Jason Hessels, and presented many of the early results from that project.

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The Art of making name badges

August 30, 2015, 5:00 pm

≫ Next: Walking the Course

≪ Previous: The Zoo of Accreting Compact Objects

In organizing a conference, a lot of work is happening behind the scenes. One of the things is making name badges. Not unimportant; like in business companies, also astronomers want to network during conferences or workshops.

At ASTRON we can rely on the creative brain of Ina Lenten at the General Affairs secretariat. She makes the design and puts everything together.

We are most grateful to Ina for providing this service, and for the reception to even deliver the badges in alphabetical order.

The photo shows the name badges for the conference Life-cycle of gas in galaxies: A Local Perspective. Taking place at ASTRON from 31 August-4 September. http://www.astron.nl/localgas2015/

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Walking the Course

August 31, 2015, 5:00 pm

≫ Next: Waveguide for Chalmers University of Technology

≪ Previous: The Art of making name badges

Following the SKA1 rebaselining exercise completed earlier this year, the time has come to focus on the science to be done with SKA1. Plans are that many large-scale key-science projects will be undertaken with SKA1, covering a very very wide range of topics. To start discussions on these projects, a SKA Key Science meeting was organised in Stockholm, attended by about 100 scientists from all over the world. The meeting made clear that the interest in the community for participating in such key science projects is overwhelming and that there are so many good ideas that it would take more than 10 SKA1s to satisfy everybody. Hence, a crucial topic on the agenda was commensality, i.e. how can we use the telescope such that one observation serves several, possibly very different, science purposes. If the community plays this well, the output of the telescope will be increased by a large factor. Discussions clearly are still in an early phase, but considerable progress was made and a clear route on how to proceed emerged.

Highlight of the meeting was the warm invitation by the City of Stockholm to visit and have dinner at the famous City Hall of Stockholm. This was very much appreciated by all participants. Not only because the City Hall is a very interesting building at a very nice location, but also because it is the venue where, on December 10 every year, Nobel laureates are received by the Royal family, followed by the Nobel Banquet in the famous Blue Hall and the ensuing Nobel Ball in the beautiful Golden Hall. Most attendants appreciated very much to be able to see these places because this is as close as they will ever get to a Nobel Prize. But the suspicion is that a few of the participants were less modest and made mental notes for 'next time'.

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Waveguide for Chalmers University of Technology

September 1, 2015, 5:00 pm

≫ Next: (Almost) perfect prediction of antenna behaviour

≪ Previous: Walking the Course

A pretty picture of some tiny parts produced by the big milling machine at ASTRON.

The NOVA team recently produced 4 special parts for Chalmers University in Gothenburg (Sweden). They are aluminium waveguides, and a proof-of-concept of an RF transmission unit with integrated electronic chip. It is a step towards an ultra low-loss mm-wave antenna system.

It took a few iterations to make the design suitable for machining. Parts like this have been produced before, but not this small. Ours consist of 24 tiny pillars of 0.4 mm wide, a gap of 0.6 mm, and 1 mm height.

We could just produce this in the classical way, with a small needle-like milling tool. For even smaller pillars we might have to switch to our 90.000 rpm spindle.

Chalmers started the integration of the parts with a small chip in the centre of the pillar structure. The next step will be to test the performance of the whole setup. Watch this space.

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(Almost) perfect prediction of antenna behaviour

September 2, 2015, 5:00 pm

≫ Next: Greetings from the Southern Hemisphere!

≪ Previous: Waveguide for Chalmers University of Technology

Getting a perfect correspondence between measurements and simulations is the ultimate goal for every antenna designer. But reality is harder than simulations.

For example, the connector is usually not taken into account in the simulation. Instead of doing that, one can try to calibrate out its effect in the measurement. This approach was chosen to verify a small 4-element Vivaldi array, based on the EMBRACE array elements. It was designed as part of the MFAA-activities within ASTRON.

The first picture shows the simulated array. Simulations were done in ANSYS HFSS version 16.0.

The second picture is a photograph of the measured array.

The third picture shows the calibration standards that were used to calibrate out the effect of the connector. This calibration kit consists of a short, a "thru" and two line standards.

The other pictures show the measured and simulated (passive) reflection coefficients of one of the array elements.

One can see that agreement between measurement and simulation is very good. The positions of the maxima and minima of the amplitude are predicted well, and also the phase behavior. This was all achieved without tweaking the simulation after the measurement. The only thing that was done after the simulation is a phase correction to adjust for the different positions of the reference planes in measurement and simulation.

Of course this work would not have been possible without nurturing colleagues. The calibration kit was designed and verified by Martijn Brethouwer, who also assisted during the measurements. The mechanical design of the array was done by Raymond van den Brink. The feedboard of the array was designed by Erik van der Wal. The feedboards and calibration standards are produced at the ASTRON PCB-facility.

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