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Articles on this Page
- 08/06/14--17:00: _Connecting with the...
- 08/05/14--17:00: _Scintillation Arcs ...
- 08/07/14--17:00: _Millisecond Pulsar ...
- 08/10/14--17:00: _ALMA Band 5 Mirrorb...
- 08/11/14--17:00: _A Deep 20-GHz Surve...
- 08/12/14--17:00: _The APERTIF Phase L...
- 08/13/14--17:00: _Becoming a H.I.T.
- 08/14/14--17:00: _An unknown hydrogen...
- 08/17/14--17:00: _Einstein cake and more
- 08/18/14--17:00: _A day in the life o...
- 08/19/14--17:00: _Probing the gas con...
- 08/21/14--17:00: _EWASS 2014 Symposiu...
- 08/20/14--17:00: _M51 observed at 151...
- 08/24/14--17:00: _Attention to Detail
- 08/26/14--17:00: _Mode-switching puls...
- 08/25/14--17:00: _Dust as Food for Ga...
- 08/27/14--17:00: _World largest Micro...
- 08/28/14--17:00: _The Great and the Good
- 09/01/14--17:00: _Low Frequency Scien...
- 08/31/14--17:00: _ASTRON News summer ...
- 08/06/14--17:00: Connecting with the Portuguese for SKA Aperture Array developments
- 08/05/14--17:00: Scintillation Arcs in the Ionosphere
- 08/07/14--17:00: Millisecond Pulsar Scintillation Studies with LOFAR: Initial Results
- 08/10/14--17:00: ALMA Band 5 Mirrorblock Production
- 08/11/14--17:00: A Deep 20-GHz Survey in the South
- 08/12/14--17:00: The APERTIF Phase Locked Loop (PLL) Unit
- 08/13/14--17:00: Becoming a H.I.T.
- 08/14/14--17:00: An unknown hydrogen cloud near spiral galaxy NGC 2403
- 08/17/14--17:00: Einstein cake and more
- 08/18/14--17:00: A day in the life of a millisecond pulsar
- 08/21/14--17:00: EWASS 2014 Symposium on Low-frequency Radio Astronomy
- 08/20/14--17:00: M51 observed at 151 MHz with LOFAR
- 08/24/14--17:00: Attention to Detail
- 08/26/14--17:00: Mode-switching pulsar B0943+10 holds yet another surprise
- 08/25/14--17:00: Dust as Food for Galaxies
- 08/27/14--17:00: World largest Microphone phased array
- 08/28/14--17:00: The Great and the Good
- 09/01/14--17:00: Low Frequency Science and Technology Symposium
- 08/31/14--17:00: ASTRON News summer edition 2014
© NL SKA OfficeWhile the Netherlands and Portugal did not play each other during the recent soccer World-championship in Brazil, radio-astronomical relations between the two countries have blossomed since the days of the European SKADS program around 2005.
Beyond Radio Astronomy, an impressive visit was paid some time ago to a huge Solar-Voltaic power plant in Moura (Portugal). Its huge size of 300.000 sqm gave an impression of the size of a future Aperture Array SKA. It made some realize that the use of renewable energies could not only fit the SKA operational power bill, but it could also contribute visibly to a more responsible society.
Against this background of ongoing SKA activities, and initiatives to look into solar power for LOFAR, a small team from IT Portugal visited ASTRON on 7-8th July, to re-establish connections. The group included industrial partners like Martifer-Solar and AST-Portugal/Netherlands. Also present were officials from Drenthe province with responsibility for renewable energies.
This meeting was made even more relevant in view of the Portuguese intention to become an (associate) member of SKA, made possible by the release of national funds. This will strengthen the Portuguese position in the SKA consortia, in particular the ones that are concerned with aperture arrays (LFAA and MFAA).
© Richard FallowsCompact radio sources twinkle ("scintillate") because of variations in density moving around in the interstellar medium, the solar wind (the continual expansion of the Sun's atmosphere through interplanetary space) and the Earth's ionosphere, in exactly the same way as the visible stars scintillate due to the Earth's atmosphere. This scintillation has been studied for many years and is used as a way of probing these density variations and gleaning information about, for example, the density and velocity of the solar wind.
When viewed as a time series, the scintillation manifests itself as rapid variations in intensity. If the received signal is also split up into a number of frequency channels across the available bandwidth, the time series' for each channel can be stacked and plotted in a dynamic spectrum which shows how the pattern of scintillation varies with both observing frequency and time.
In modelling the scintillation, we often assume that the signal is scattered by a "thin screen" of density variations (imagine an irregular grid through which light might be diffracted), moving at a certain velocity relative to the radio source. The scattered waves then interfere as they travel further from the screen and the resulting interference pattern is what we receive as scintillation. Multiple thin screens along the line sight can be used to model scattering due to a thicker medium.
Now imagine pairs of waves being scattered by the thin screen: Each pair of scattered waves has a Doppler shift due to the movement of the screen and a time delay between them due to the different path length that each wave has likely followed. A "map" of these Doppler shifts and time delays between every pair of scattered waves can be formed by taking the so-called "secondary spectrum" - effectively the 2-dimensional power spectrum (squared amplitude of the 2-dimensional FFT) of the dynamic spectrum. When this analysis is applied to pulsar observations to study scintillation in the interstellar medium, a clear arc structure termed a "scintillation arc" (first discovered by Dan Stinebring in 2001, is often seen. Over the years this has proved an invaluable tool for probing the interstellar medium.
For the first time (we believe), scintillation arcs have now been found in the secondary spectra of ionospheric scintillation seen in observations of Cygnus A taken using the Kilpisjarvi Atmospheric Imaging Receiver Array (KAIRA - the station built using LOFAR hardware in Arctic Finland). It is believed that these also represent the first such broadband (relative to the observing frequency) observations of arcs due to any scattering medium and also the first found using LOFAR hardware. These results have now been written up in a paper recently submitted.
The image shows an example segment of dynamic spectrum and an example secondary spectrum, with the x-axis being Doppler shift and the y-axis being a parameter equivalent to time delay.
© Anne ArchibaldStars twinkle because the turbulent atmosphere creates interference patterns in their images. At radio frequencies, the atmosphere doesn't affect the signal (much), but the interstellar medium does. The very tenuous plasma - about one atom per cubic centimeter, as a rule of thumb - bends and delays the radio waves very slightly. Since there are a lot of centimeters between us and a pulsar, this effect leads to multi-path propagation: some of the signal from the pulsar is delayed by travelling along slightly longer paths. This effect gets stronger at lower frequencies, so as you can see in the top left image, the pulse from this pulsar gets progressively more smeared out as one moves to lower frequencies.
This smearing effect can be a problem for precision timing of pulsars because the amount of smearing varies from week to week. It is also difficult to study because the intrinsic pulse shape of the pulsar also changes with frequency. Fortunately, there is another effect of the multi-path propagation: the signals coming along different paths interfere with each other, producing a pattern of constructive and destructive interference that can be seen by looking at the brightness as a function of frequency. The top right image shows two peaks in this interference pattern. Note that they are only a few kilohertz wide! This complicates the analysis, since the pulsar's spin frequency is nearly a kilohertz.
The few bright peaks in this interference pattern are also surrounded by a great deal of noise. We therefore used an autocorrelation to effectively add up all the peaks, giving us a measurement of the average peak width, shown in the bottom left image. This average peak width is roughly the reciprocal of the amount of smearing shown in the top left panel, and its dependence on frequency (shown in the bottom right panel) can potentially tell us how the turbulent interstellar medium behaves.
This image is based on the paper Millisecond Pulsar Scintillation Studies with LOFAR: Initial Results, by Anne Archibald, Vlad Kondratiev, Jason Hessels, and Dan Stinebring.
© NOVAIf you happened to be around in the small hours of the night recently, you might have heard the milling machine (still) running. It loyally and untiringly worked for us through the night, making mirror blocks for ALMA band 5. In an 18 hour production run, it produced 4 complete blocks, while an additional 2 hours were needed for some deburring, laser engraving of the serial number, and packing and setting up the next run.
All this was made possible by a smart redesign by Niels Tromp (NOVA-ASTRON) that reduced the number of separate parts from 5 to just a single accurate part with 2 integrated mirrors. By a combination of clever milling strategy, focus on quality, smart production by Menno Schuil, Niels and the team of NOVA/ASTRON, and measurement by SRON Groningen, the production went pretty well and might be finished when this daily image is finally published.
ALMA (Atacama Large Millimeter Array) is a mm and sub-mm wave interferometer. The ALMA band 5 is covering the 162-211 MHz (1,4-1,8 mm) wavelength.
© Tom FranzenA team of astronomers, led by Tom Franzen (CSIRO) and including ASTRON astronomer Elizabeth Mahony, have recently presented the source catalogue and first results from a deep, blind radio survey carried out at 20 GHz with the Australia Telescope Compact Array. The Australia Telescope 20 GHz (AT20G) deep pilot survey covers a total area of 5 square degrees in the Chandra Deep Field South and in Stripe 82 of the Sloan Digital Sky Survey and was observed at 5, 9 and 20 GHz down to a flux density limit of 2.5 mJy.
One of the interesting results found in this study is that there is a strong and puzzling shift in the typical spectral index of the 15-20 GHz source population when combining data from the AT20G, Ninth Cambridge and Tenth Cambridge surveys: there is a shift towards a steeper-spectrum population when going from 1 Jy to 5 mJy, which is followed by a shift back towards a flatter-spectrum population below 5 mJy. Comparing with source count models of high-frequency radio sources (which include contributions from FRI and FRII radio galaxies and star-forming galaxies) does not reproduce the observed flattening of the flat-spectrum counts below 5 mJy. It is therefore possible that another population of sources is contributing to this effect. A link to the published paper can be found here: http://adsabs.harvard.edu/abs/2014MNRAS.439.1212F
Image: On the left is shown the 20 GHz map of the 03 hr field produced by combining approximately 3500 individual maps (top panel) and a zoomed in region (bottom panel). On the right are plots showing how the fraction of steep spectrum sources changes as a function of flux density. Two different cutoffs in spectral index are used: the percentage of sources steeper than -0.8 is shown in the top panel and the percentage of sources steeper than -0.5 shown in the bottom panel.
© ASTRON, 2014Just some impressions of the APERTIF Phase Locked Loop Unit (PLL) which was installed in radiotelescopes 2 and 5 at the Westerbork site on June 24th.
The PLL is a vital part of the Local Oscillator Generation system (LOG). With the LO-Generator Control Board, the Divider Unit and the Buffer Board (both coming soon to your AJDI) they form the LOG Subrack. Two of the LOGs are connected to the APERTIF Down Converter Units (DCU), (see also here). These systems mix down the antenna signals to the baseband so that the Analog-to-Digital Converter Unit (ADU) can convert it eventually to a digital data stream.
Design and production of the PLL unit is another good example for the outstanding collaboration between our mechanical and electronic department here at the ASTRON labs. Keeping phase drift between the different units under control was a big challenge, but fruitful discussions between mechanical- and radio engineers have led to a well performing system at reasonable cost. The slideshow depicts some aspects of mechanical design, control soft- and hardware development and the qualification in the climate chamber.
© Chris GullThe Hanze Institute of Technology (H.I.T) in Assen is a department of the Hanze Hogeschool Groningen. It offers a 4-year bachelor-plus programme in Advanced Sensor Applications (ASA). Since 2011, the ASA-programme has been ranked as "excellent" in the category Electrical Engineering.
The H.I.T. was founded on February 6th, 2008, in close cooperation with important employers in the region like N.A.M. (Shell/Esso), Sun Microsystems, and ASTRON. The intention is to strengthen the high-tech infrastructure in the northern part of the Netherlands.
For the 5th year in a row, ASTRON has actively been contributing to the educational program. In Theme 8 ("Meaningful Data"), in the 2nd Study Year, ASTRON contributes expertise, lectures, practical skills and project tasks based on signal processing. In addition, we provide a part-time professor for the Master Program.
H.I.T.-students easily find their way to stimulating jobs in industry and scientific institutes like Philips NatLab. Several of them have done their graduation project at ASTRON.
© Erwin de BlokOne of the unanswered questions about galaxies is where they get their gas from. When galaxies form stars, they consume their gas. Measurements show they do not contain enough gas to sustain their star formation for a long time. ASTRON astronomer Erwin de Blok is part of an international team (led by D.J. Pisano from West Virginia University (US)) that uses the Green Bank Telescope (GBT) to search for very faint gas around nearby galaxies to see if they are acquiring gas from their environment.
One of the galaxies studied is NGC 2403. With the GBT the faint signal of an hitherto unknown neutral hydrogen (HI) cloud was discovered outside the main gas disk of NGC 2403. Comparison with deep HI data obtained a number of years ago with the VLA showed that the cloud is most likely associated with a filament of gas in the inner disk that shows peculiar velocities. The cloud and filament probably form one single complex.
There are several possible explanations for this cloud/filament complex. The most likely two are that we are seeing gas being accreted by the galaxy, or that we are looking at gas expelled from the disk due to the passage of smaller galaxy. A study of the rest of the survey should show how frequent these events are, and help explain them.
The picture shows an optical image of NGC 2403 from the SDSS in the background, overlaid in blue with a VLA HI map. The newly discovered cloud is visible as the diffuse emission shown in red in the top-right corner. The filament is shown superimposed on the main disk in white/red colours.
The paper describing this result is available at http://arxiv.org/abs/1407.3648 . It has also been accepted for publication in Astronomy & Astrophysics.
© Roel WitversOn wednesday July 2nd, a (g)astronomical competition came to it's bubbling climax: an expert panel, consisting of experts of various sorts, judged the Milky Way cocktails and Dark Matter dishes that had been prepared by local and not so local school kids. The latter rose to the inspiring challenge by offering smashing smoothies, crispy cookies and darkly mysterious cakes.
The panel, consisting of real ASTRON astronomers, R&Ders and other experts, performed a proper review as if it was an SKA system design. The marks for the various contributions were motivated by means of serious mini lectures that touched on Black Holes, advanced (space) technology and good taste, linking the review with the intentions of the contenders.
The event was organized in connection with the youth novel "Het Logboek" by Anke den Duyn, due to be published in Sept 2014. Just like the novel, the event endeavoured to forge a link between the general public and day-to-day ASTRON business.
© Cees BassaOn June 22 and 23rd, 2013 nine telescopes, spread around the world, joined together to observe a millisecond pulsar continuously for 24 hours. The Parkes telescope in Australia started the campaign, subsequently handing over to the GMRT in India, the European telescopes in Germany (Effelsberg), France (Nancay), the United Kingdom (Lovell) and the Netherlands (both WSRT and LOFAR), to end with Arecibo and Green Bank in the United States. This project was undertaken for the International Pulsar Timing Array (IPTA), which uses a set of accurately timed millisecond pulsars to directly detect gravitational waves.
The millisecond pulsar chosen for this project is PSR J1713+0747. This pulsar is the most precisely timed pulsar in the IPTA project. The primary goal of this global observation is to characterize the timing noise of the pulsar on time scales ranging from one hour to one day. An overview of the project has recently been published.
Though the focus of this global observing session was at observing frequencies around 1.4 GHz for studying timing noise, the unique capabilities of WSRT and LOFAR were used to obtain data at 350 MHz and 150 MHz, respectively. Observations at these low frequencies are crucial to study variations in the dispersion measure (a proxy for the electron column density towards the pulsar), which is one of the other main sources of noise in high precision pulsar timing.
The top figure shows the J1713+0747 pulse profile at L-band (1.4 GHz, all telescopes except LOFAR), 350 MHz (WSRT) and 150 MHz (LOFAR). The pulsar is much weaker at lower frequencies, hence the lower signal-to-noise. The L-band/1.4 GHz dynamic spectrum is shown in the bottom panel. An intricate scintillation pattern is seen. The contributions of the different telescopes are indicated.
© Katinka GerebAccretion onto the central black hole of galaxies is thought to be connected with the presence and kinematical properties of the gas. In radio-loud active galactic nuclei (AGN), neutral hydrogen (HI) absorption studies provide a key tool to trace the cold gas component that may play a role in these processes. From previous studies it appears that compact radio sources, which are likely to be young AGN, are embedded in an HI-rich medium, and this may be connected with the triggering of AGN activity.
We carried out a systemic search for HI absorption in a relatively large sample of 101 radio AGN. Despite our shallow, 4-hour observations with the Westerbork Synthesis Radio Telescope (WSRT), we obtain a direct detection rate of 30%, similar to deeper studies. The detection rate does not depend on the apparent flux of a source, suggesting that HI absorption studies of even fainter radio sources will bring a large number of detections.
For the first time, we carried out a spectral stacking analysis of HI absorption. We find a dichotomy in the presence of HI in the sense that even when a large number of spectra are averaged, galaxies that do not show HI absorption in their individual spectra remain undetected (Fig. 1). The dichotomy suggests that in many galaxies, HI must be in a flattened structure so that orientation effects play a role. However, orientation effects alone cannot fully explain the dichotomy, suggesting that some galaxies must be depleted of cold gas.
Compact sources show higher detection rate, optical depth and Full Width at Half Maximum (FWHM) than extended sources (Fig. 2), strongly suggesting that different gas conditions exist in these two types of radio sources. It seems that nuclear activity in most of the young AGN is connected with the presence of unsettled gas.
These results have been presented in a A&A paper now in press by Gereb, K; Morganti, R; Oosterloo, T; http://arxiv.org/abs/1407.1799
© Raffaella Morganti et al.The Symposium "Exploring the Low-frequency Radio Sky in the SKA Era" was held in Geneva, Switzerland from 30 June - 01 July as part of the 2014 European Week of Astronomy and Space Science. This two-day Symposium, organized by members of ASTRON's Astronomy Group, brought together approximately 40 members of the low-frequency radio community from all over the world including Europe, Australia, South Africa, India, and the US. The program included a wide range of science topics, as well as technical updates from all the currently operating low-frequency instruments.
The Symposium kicked off with a session on the newest generation of low-frequency radio facilities including LOFAR, MWA, and the LWA. George Heald gave an update on LOFAR's current capabilities, while Randall Wayth summarized progress with the MWA and Tracy Clarke presented the status of the LWA. Updates on low-frequency observing with the JVLA and GMRT were given by Rick Perley and Yashwant Gupta, respectively. SKA Science Director Robert Braun concluded the instrumentation session with a look ahead to the low-frequency capabilities of the SKA.
The Symposium featured a broad scientific program covering such extragalactic topics as large, all-sky surveys to cluster relics and halos, AGN, and the Epoch of Reionization. The remainder of the second day was filled with a wide variety of presentations on galactic science, pulsar studies, transient surveys, and solar studies. ASTRON and LOFAR figured prominently during the meeting with many members of the ASTRON Astronomy Group and Radio Observatory giving talks and presenting recent results.
The modest size of the meeting made for a great informal atmosphere with many questions and discussion throughout the course of the two days. All in all, the meeting was a great success and brought together a truly representative subset of the international, low-frequency radio community.
© David Mulcahy (MPIfR)Nearby spiral galaxies have hardly been studied in the very low radio frequency range (less than 300 MHz) due to many technical challenges. Up to now, the only observations of galaxies at these frequencies were of poor resolution and no details could be made out. This is now changing with the start of operations of the brand new radio telescope, the Low Frequency Array (LOFAR).
Low-frequency radio synchrotron emission of nearby galaxies is very important as it is produced by aged and low-energy electrons that are less affected by energy losses and therefore can propagate further away from their site of origin.
A team of astronomers from several countries in Europe, including Germany, the Netherlands and the UK, have been able to observe Messier 51, aptly named the 'Whirlpool Galaxy', with LOFAR at a frequency of 151 MHz. It is the most sensitive image of any galaxy at frequencies below 300 MHz so far. With this sensitivity, the disk of M51 can be seen to extend further than ever seen before in the radio regime.
Interestingly, the disk of M51 does not extend as far out as expected due to steepening of the radial profile of the radio emission beyond the star forming regions.
With LOFAR's high angular resolution, the grand design spiral arms are visible and compared to higher frequencies are becoming broader due to cosmic ray diffusion. Using simple models it is seen that diffusion is the most dominant process of cosmic ray propagation in M51. While M51 was not detected in polarised emission due to very high amounts of depolarisation caused by interstellar turbulence within the galaxy, polarised emission emanating from 6 background radio galaxies was detected in the entire field.
The paper describing this result is published by Astronomy & Astrophysics and available at
© Madroon Community Consultants (MCC)The unusual success of institutes like ASTRON or JIVE is rooted in many factors, and one of them is an unusual attention to detail. Not many people would notice that even the license plates of our small fleet of limousines proudly reflect a significant part of our core business(****).
Part of our core business is to make (ultra) high-quality images of the radio sky, using arrays of radio antennas. An important problem is the instrumental Point Spread Function (PSF) pattern around all radio sources, which often takes the shape of rings or radial spikes. Since the magnitude of the PSF is proportional to the source flux, the patterns around bright sources tend to obliterate the much fainter radio sources in which we are interested. For a sparsely sampled imaging instrument like a radio aperture synthesis array, the PSF extends over the entire field(***), and has to be removed from the data with extreme accuracy(**). After all, one cannot study what one cannot see.
Fortunately, we are very good at subtracting unwanted radio sources (and their PSF). Our instruments are designed with unusual care, and our data reduction software is unusually sophisticated. As a result, the unofficial world record has been held by our WSRT for many years, with a Dynamic Range(*) of well over one million. At this moment, the record is briefly held by one of our esteemed competitors (the JVLA), but only by using software that was developed at ASTRON. We expect that the Blue Riband of Dynamic Range will soon be recaptured again by LOFAR, in its search for the elusive Epoch of Reionization.
This obsession with getting the most out of our imaging instruments may have seemed a bit of a luxury pursuit in the past. But it has proved to be an essential preparation for the new generation of giant radio telescopes, like LOFAR and SKA. These will require an even higher dynamic range, and a PSF with carefully controlled sidelobes, to exploit their much greater sensitivity. And since the devil is in the details, these require unusual attention.
(*) The Dynamic Range (DR) of an image quantifies the ability to see faint objects in the presence of (the PSF of) very much brighter ones in the same field.
(**) A bit like removing the Sun from the daytime sky, so we can see the stars.
(***) For a fully sampled imaging instrument like an optical telescope, the PSF is much smaller, so it only ruins a small area around bright sources.
(****) Apart from the magic letters PSF, the license plate indicates that our images get very close to the Truth (symbolized by the number 42), and that a Dynamic Range of 6 orders of magnitude is a minimum requirement for club membership.
© Anna Bilous, LOFAR PWGPSR B0943+10 is one of the best examples of the rare class of mode-switching pulsars. Unlike most of the pulsar population, B0943+10 has two stable modes of radio emission, each with its own distinct radio profile morphology and sinlge-pulse behaviour. The pulsar switches between "Bright" and "Quiet" modes once every few hours and the transition takes less than a few stellar rotations. The switch in the radio modes is also accompanied by changes in the X-ray emission mode, which was discovered using LOFAR, GMRT and XMM-Newton (Hermsen et al. 2013). This paper demonstrated that mode switching is a rapid and global transformation of the magnetosphere and its broadband emission. The exact nature of this transformation, however, is still far from being well understood.
With the goal of better illuminating the difference between the two modes, we carried out sensitive, multi-hour LOFAR LBA observations as part of Cycle 0 (Bilous et al 2014). Below 100 MHz the frequency-dependent changes in the pulse-profile morphology are the largest and effects too subtle to see at higher frequencies become readily evident. Luckily, B0943+10 has one of the steepest spectra of all known radio pulsars, and is easily detected in the LOFAR low-band.
We found that in both modes the profile evolution with frequency can be well explained by "radius-to-frequency mapping" (i.e. the emission height grows towards lower emission frequency, as depicted by the colours above) at altitudes within a few hundred kilometres of the stellar surface. Also, despite the seemingly different behaviour of the profiles, we find that radio emission comes from virtually the same range of heights if both modes originate at the same magnetic latitude.
Quite surprisingly, and perhaps more interestingly, we also discovered that during the Bright mode the average profile shifts gradually towards later spin phase and then resets its position at the next Quiet-to-Bright transition. This is illustrated above (left-hand side), with the magnitude of shift amplified by a factor of 4 for clarity. Such a delay is puzzling as it is frequency-independent and much too large to be due to changing spin-down rate. One possible explanation for the delay is a variation of the accelerating potential inside the polar gap, which then causes changes in the corotation velocity of the plasma in the open field line region. This explanation connects the observed profile delay to the gradually evolving subpulse drift rate, which depends on the gradient of the potential across the field lines. It shows that the Bright mode is not completely static but evolves in a systematic and reproducible way before suddenly switching back to the Quite mode. We hope that this added piece in the puzzle will help us gain a better understanding of the underlying physical mechanism behind pulsar mode switching.
© NOAO, HST, ASTRONGalaxies can be dusty. And dust appears in galaxies (like it does in daily life) as dark patches. In the case of galaxies, it is blocking the light of the stars. Some examples are shown in the image. However, dust is also consider to represent a good tracer of fuel that can "switch on" a black hole and produce an "active" galactic nucleus (AGN).
To investigate and confirm this, we have we have used deep observations of radio galaxies from the Herschel Space Observatory to estimate the dust masses of their host galaxies, compare this with non-active galaxies and thereby investigate the triggering mechanisms for their quasar-like AGN.
The dust masses derived for the radio galaxies (7.2*10^5
These results have been presented in a paper accepted for publication in the Monthly Notices of the Royal Astronomical Society "The dust masses of powerful radio galaxies: clues to the triggering of their activity" by
C. Tadhunter, D. Dicken, R. Morganti, V. Konyves, N. Ysard, N. Nesvadba, C. Ramos Almeida (a copy of the paper can be found at http://arxiv.org/abs/1408.3637).
A collection of information for the radio galaxies studied can be found at http://2jy.extragalactic.info/2Jy_home_page.html
© Foto (inserts): (c) Sorama (c) ASTRONLast Friday, 22th of August, Dutch company Sorama sets a record when combining four of their 1024 microphone arrays to one large 4096 elements array. The previous record of 1020 microphones from Massachusetts Institute of Technology was over classed by merely a factor of four! The new record will be listed in the Guinness Book of Records.
Sorama is using coherent sampling and beamforming technologies to virtually create a sound camera. By using a large number of MEMS based microphones, they are able to create images with resolutions high enough to localize (pinpoint) and identify sources of audible noise. Visualizing sound waves around and vibrations on a product helps to understand and improve the dynamic behaviour of a product (e.g. localize and reduce sound vibrations in consumer electronics, resulting in quieter products). Another application example is to monitor vibrations of engines and to analyse the results of damping measures to reduce the environmental noise generated from these machines.
Just like ASTRON applies GPU cores in its new COBALT beamforming/correlator system, Sorama also recognizes the power of GPUs when implementation their acoustic algorithms for beam forming and near-field acoustic holography.
During the Hannover Messe where both Sorama and ASTRON joined the Dutch High Tech pavilion, early discussions started on the feasibility on creating more spatially distributed microphone arrays. Although the sampling rate of microphone arrays differs significantly from sampling rates as used in radio telescopes like LOFAR , there is reason enough to believe that we could exchange know-how on clock distribution and coherent sampling and beamforming technologies.
Congrats to Sorama for its world record!
© asperaThis jolly gathering of the Great and the Good is celebrating the award of the 2014 Grote Reber medal to Ron Ekers during the recent General Assembly of the URSI(*) in Beijing. This highly prestigious prize is awarded by the Grote Reber Foundation, normally annually, to individuals of any nationality or country of residence, for outstanding and innovative contributions to radio astronomy.
NB: If you are a radio astronomer, and do not know everyone around this table, you are not ambitious enough. And if they do not know you, you are not (yet) important enough.
(*) Radio astronomy is part of the International Radio Science Union (URSI) because the field was started by radar engineers, which slowed its acceptance by "real" astronomers into the International Astronomical Union (IAU). Until the Nobel prizes started rolling in...
© SHAOAt the August 14-15 Space-based Ultimate Low Frequency Radio Astronomy Symposium at the Shanghai Astronomical Observatory (SHAO), scientists from China and Europe discussed future satellite missions aimed at radio astronomy at frequencies below the Earth's ionospheric cut-off. Two- and three dimensional constellations of up to 12 satellites, in Moon orbit and at the Sun-Earth L2 Lagrangian point, were discussed both from scientific and technology perspectives. Such missions would open up the last, virtually unexplored, frequency range.
Vivid discussions helped clarify the properties of the concepts, and the range of science cases which can be supported by a distributed set of micro and nano-satellites. As many scientists at the workshop also attended the URSI in Beijing in the following week, most of them took the opportunity to visit the Chinese National Space Science Centre (NSSC) on August 20th, to continue discussing science and mission details.
The SHAO workshop and the NSSC meeting also served as preparation for presenting a radio mission concept at the upcoming ESA-CAS September 23-24 Copenhagen meeting. The latter is aimed at planning for a joint scientific space mission, and is initiated by the European Space Agency (ESA) and the Chinese Academy of Sciences (CAS). A call is expected by the end of this year, mission selection by the end of 2015, and launch is aimed at 2021.
The picture shows participants at the Low Frequency Science and Technology Symposium in SHAO Shanghai.
© ASTRONThe summer edition of ASTRON news has hit the streets - don't miss out on the latest news from ASTRON!