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

older | 1 | .... | 53 | 54 | (Page 55) | 56 | 57 | .... | 71 | newer

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    © CC-BY-4.0 Tammo Jan Dijkema

    Stellarium is a great computer planetarium program, also for non-astromers. CAMRAS uses it in the Dwingeloo telescope to show where the telescope is pointing. Unfortunately, none of the default landscapes look anything like the surroundings in Dwingeloo. That's why I made a custom landscape.

    I took the photos from the top of the telescope, using it as a 130 tonne rotating tripod (this is why the telescope itself is absent from the picture). The many photos were then stitched together by the open source panorama tool Hugin. I more or less followed this guide for the conversion to a real Stellarium landscape.

    Incidentally, the screenshot also shows that the current favorite object of the telescope PSR B0329+54 is often right above the Astron building, highlighting the need for radio quiet at Astron.

    Unfortunately, the day I shot the photos it was a bit foggy and there were machines on the road; I intend to make a better version some day. In the meantime, you can install this version 0.1 yourself.

    To install the Dwingeloo landscape in your own Stellarium, download it, go to "Sky and viewing options [F4]", and under the tab "Landscapes" choose "Add/remove landscape".


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    © ASTRON, Oxford University Press, WIYN / William Keel / Anna Manning

    The timescales over which galaxies form and evolve are outside the reach of human life. Thus, astronomers need to use indirect methods to derive the history of galaxies.

    Important events happen during the life of a galaxy and they can change the course of its evolution. In particular, when the central supermassive black hole (SMBH) is active, it can release huge amounts of energy which can affect the surrounding gas and can impact the evolution of the entire galaxy. This effect has been recognised as crucial for explaining why galaxies look the way they do.

    But how often and for how long is a SMBH active?

    This is not an easy question to answer. Astronomers are working hard to address it by using observations in different wavebands and perform a kind of ‘archaeology’ to trace the signatures of past nuclear activity. Extremely interesting is the role that the low-frequency radio telescopes and, in particular, LOFAR have in this. They offer new possibilities for major steps forward in this field. At low radio frequencies, where low-energy electrons can radiate for longer times, the astronomers can explore the phases in which a radio source is dying and, in some cases, is re-borne: an ideal task for LOFAR.

    The status of the field and the progress on this fascinating topic are described in a review article appearing this week in Nature Astronomy, “Archaeology of active galaxies across the electromagnetic spectrum (https://www.nature.com/articles/s41550-017-0223-0 )” by Raffaella Morganti (a download can also be found at http://rdcu.be/vlUw ). Among many things, the review summarises some of the recent results obtained by LOFAR, including those from the ERC-RadioLife group.


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    © ASTRON 2017

    We have three main software development groups within ASTRON: Research&Development, Radio Observatory and Science Data Centre. Earlier this year an initiative was started by the ASTRON management under guidance of Gert Kruithof to harmonize and improve the development processes across these groups. Various topics have been identified and currently the group is working in regular meetings to handle these topics one by one. Topics include Documentation, Coding Standards, Code Review process, Tools like issue tracking, Handover from R&D project to operational development and maintenance, etc... The effort is currently being led by Ronald Nijboer and Jasper Annyas. These are images of our first meeting where we used sticky notes to identify and group topics.

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    © (c)2017 S.Damstra ASTRON

    Microserver T4240 Standalone version.

    The standalone microserver with a Freescale T4240 multicore processor arrived this week at ASTRON and is now up and running.

    The T4240 multicore processor features 12 physical high performance cores.

    The operating system is a Linux distribution of Fedora 23.

    The standalone microserver is small and therefor powerefficient.

    It can easily be accessed using a SSH or a VNC session. One of the pictures shows the VNC session.

    In that way you can work on the desktop of the microserver.


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    © Emma Alexander, Jess Broderick

    Radio recombination lines (RRLs) arise from transitions between highly-excited levels of atoms in the interstellar medium (ISM). Low-frequency ( Oonk et al. (2014) for a full review.

    As the SKA heads into the critical design review stage of the engineering process, on-site testing is crucial. For example, the Engineering Development Array (EDA) is an SKA1-Low prototype system in Western Australia (Wayth et al., 2017). In this summer project, an exploratory 3-hr spectral line observation was taken by the single-station EDA towards the Galactic centre, although without a dedicated calibrator scan. Normalised spectra in optical depth units were produced, and multiple known RRLs were stacked after conversion to LSR velocity.

    The top two panels show two of these stacks at different frequency ranges, with Gaussian curves used to fit the lines. Carbon alpha and beta RRLs are observed in absorption between frequencies of ~40-95 MHz, and carbon alpha lines are seen in emission between ~180-230 MHz. Hydrogen alpha RRLs are seen in emission between ~70-95 and ~140-230 MHz (intermediate frequencies are dominated by RFI). The central velocities and widths of the lines are consistent with previous studies of the Galactic centre (e.g. Kantharia & Anantharamaiah, 2001).

    The lower two images show how integrated optical depth varies with quantum level, n, for both carbon and hydrogen RRLs. While broadly consistent with previous similar investigations, and therefore encouraging as a proof of concept, a thorough exploration of the calibration is needed first before we can confidently constrain properties such as the electron density and temperature of the regions that the lines originate from.


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    © astron

    While we are waiting to start commissioning Apertif using the full field of view (i.e. using 39 all beams), we can test other important characteristics of the system to see whether they match the needs of the astronomers so that new and exciting science can be done.

    A key parameter is the stability of the spectral response of Apertif (the bandpass). This is of particular importance for the study of the gas in radio sources where we want to trace the presence of diffuse and faint neutral hydrogen that has extreme kinematics (i.e. very large outflow velocities). Such gas is one of the signatures of the feedback effects of the active super massive black hole on the rest of the galaxy.

    The good performance of the old WSRT system - where we could reach a level of 1/10000 in the stability of the bandpass - did allow to discover the existence of such gas, a finding completely unexpected and still not fully explained!

    Plans are to use Apertif to expand the heritage left by the WSRT and to search for many more cases of gas with extreme kinematics. Although test observations show that the present bandpass stability of Apertif is not quite yet at the level of the old WSRT, still the first results are showing that we are on the right track.

    The figure shows one of the radio galaxies (contours of the continuum emission on the left) and (on the right) the HI absorption observed with Apertif (black line). The Apertif data are superposed to the profile obtained years ago with the old MFFE receiver of the WSRT (red line).

    Despite the higher noise (due to the limitations of the present Apertif system), the shape of the absorption is well reproduced and a hint of the presence of gas with extreme kinematics (the blueshifted, shallow wing) is also appearing. This is very promising for the future Apertif surveys and, in particular for the Search for HI absorption with APERTIF (SHARP) project.


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    © TAO

    Everyone who has ever seen a total solar eclipse will agree that it is one of the most spectacular events you will ever witness in your entire life. So when the idea came up to organise a conference this summer to celebrate the career of Jacqueline van Gorkom, it seemed a very good idea to let the time and location of that meeting coincide with that of the Great American Eclipse (the total solar eclipse of August 21, 2017, which crossed the entire USA). As a result, in the week of August 21, friends and colleagues of Jacqueline van Gorkom came together in the small town of Stanley, high in the mountains of Idaho and exactly on the line of totality of the eclipse. To discuss the latest concerning "Gas and Galaxy Evolution", one of Jacqueline's favourite topics. And to watch the eclipse.

    The career of Jacqueline started in Groningen (PhD in 1980 with Miller Goss on WSRT observations of radio recombination lines), but most of her academic life she spent in the USA (mostly the VLA in Socorro, and Columbia University, New York). Nevertheless, her ties with Groningen radio astronomy have always remained strong, to this day. This long-time connection with Groningen can be seen in the picture above, which shows the Groningen and ex-Groningen attendees of the meeting (and Jacqueline herself of course) that have, at some point in time, worked with Jacqueline. All generations are present.

    The insets are pictures yours truly took of the eclipse. As Woody Sullivan (who gave a wonderful public lecture on the eclipse) expressed it: "The eclipse was awesome. Not in the sense that this word is often used nowadays, but in its true sense: something which inspires awe. It hits you in the stomach."


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    © ASTRON OR

    Maybe you have noticed that a large number of people in the picture above are walking around at ASTRON/JIVE today. These 17 people are members of the NWO Central Works Council (NWO-COR). Today, Tuesday 12 September 2017, the NWO-COR meets at ASTRON/JIVE.

    The NWO-COR represents the employers of entire NWO (NWO-D and NWO-I) and has far reaching advisory rights towards management decisions and policies. As such, the council plays an important role in the continuity of the organization as a whole.

    Recently, the council has advised about the “legal merger of the CWI, NIOZ, ASTRON, SRON and NSCR into NWO-I per 1 January 2018” and about the “changes in the organization of NWO-I with respect to distribution of competences and its impact on personnel”. At the moment negotiations for the “uitvoeringsregelingen” (=UVR), which comprise so-called secondary working conditions, are about to begin. Therefore, the UVR is an important topic on the agenda for the central works council.

    The central works council meet in all the different parts of NWO in a rotating fashion, allowing its members to learn about all the parts they represent.

    In order to spread the workload, the central works council formed different committees, like CPZ (Personnel), COF (Organization and Finance), UVR and CCC (Communication). This morning, the committees “CPZ” and “COF” of the central works council will meet. In the afternoon, a regular central works council meeting take place.

    In the late afternoon, a small tour around the Dwingeloo and Westerbork sites is scheduled for the members of the central works council.

    The ASTRON OR thank all the people that make the tour possible.


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    © Leonid Petrov

    It is not an exaggeration to say that the date September 15, 2016 split astrometry into two epochs: before and after Gaia.

    I will provide the overview of VLBI absolute astrometry programs in the last 3 years and describe the main result: the Radio Fundamental Catalogue (RFC) of 14,768 sources. Comparison of the RFC against Gaia DR1 showed a striking peculiarity: the directions of offsets of Gaia and VLBI positions of matching active galactic nuclei shows a strong anisotropy with a concentration along parsec-scale radio jet directions.

    I argue that the most probable explanation of such an anisotropy is the presence of optical structure at scales 1-200 mas, i.e. below the Gaia resolution.

    This discovery has a number of interesting observational consequences and has a profound impact on future VLBI astrometry programs. In some cases we will be able to reveal milliarcsecond-scale optical structure that cannot be studied directly with optical telescopes. We will be in a position to pinpoint in which area the optical flares occur: in the accretion disk, at the jet base (core) or at the hot spot on the extended jet.

    Future observational programs will be outlined.


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    © ASTRON

    The commissioning of Apertif is progressing steadily and observations are now being done on a regular basis. The purpose of these observations is to test and validate the system characteristics of Apertif. To do this, it is usually not necessary to use all beams to image the full field of view of Apertif because the data from one or two beams give enough information for the test performed (and it saves a lot of data reduction�). But occasionally the full field of view is used to see if everything fits together in the way it should.

    The image shown above is from a recent Apertif observation of the Lockman Hole using 37 beams giving useful data over about 10 deg^2. Eight antennas were used and only 70 MHz in one polarisation. The noise of the image is 0.2 mJy/beam, so about half that of the NVSS. The final Apertif images will be ten times deeper. The calibration and imaging was done using the automated Apertif calibration procedures.

    The Lockman Hole is an important region on the sky. The Galactic foreground is very low in this direction, so it is very suitable for deep extra-galactic astronomy. It has been observed in every waveband, by more or less every telescope that can see it, so there is a wealth of information available for this part of the sky. Also LOFAR has observed the Lockman Hole (there are ten other Astron/Jive Daily Images on it) and in particular the combination of LOFAR with Apertif data will be very powerful, so you will see more of this region in the near future.


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    © NAOC

    On 15 September 2017, our good friend Nan Rendong died while in the US for a final treatment for his long cancer.

    Nan came to ASTRON in 1983 as an exchange 'student' to study radio astronomical methods, VLBI and processing. He became a dear friend and colleague, and his stay started a special tie between ASTRON and the NAOC which benefit both institutes. The contacts resulted in the Chinese 'small-N' proposal for the SKA, en the subsequent building of the FAST telescope.

    His influence on Chinese radio astronomy has been extensive. It is best given in the official announcement of his death at:

    http://www.bao.ac.cn/xwzx/ttnews/201709/t20170916_4860637.html?from=timeline&isappinstalled=0

    which is roughly translated as:

    Posted: 2017-09-16

    Obituary

    China's famous astronomer, Chinese Academy of Sciences National Astronomical Observatory researcher, the national major science and technology infrastructure projects - 500 meters caliber spherical radio telescope (FAST) project chief scientist, chief engineer, former Beijing Observatory Deputy Director Mr. Nan Rendong in Beijing time 2017 Year on September 15 23:23 died due to illness, at the age of 72 years old.

    Mr. Nan Rendong is the initiator and founder of the FAST project. Since 1994, he has been responsible for FAST site selection, pre-research, project, feasibility study and preliminary design. As the chief scientist and chief engineer of the project, he is responsible for compiling the FAST scientific goal, guiding the construction of FAST and guiding a series of technical problems such as fatigue and moving cable, and has made outstanding contributions to the successful completion of FAST project. FAST known as "China Eye", is China's own intellectual property rights, the world's largest single-caliber, the most sensitive radio telescope. Mr. Nan Rendong is one of the earliest Chinese astronomers who have held important positions in the International Astronomical Society. He is also an outstanding comprehensive technical expert. He is a well-established expert in astronomy and astronomy and technology. He has cultivated a great deal of science and technology Talent.

    Mr. Nan Rendong lived generously, indifferent to fame and fortune, treat people sincere, mind the overall situation, spared no efforts for the development of China's astronomy has made outstanding contributions. His unfortunate death is a major loss of Chinese astronomy! We are mourned and deeply remembered Mr. Nan Rendong!

    Mr. Nan Rendong immortal!

    Follow his explicit wishes, and do not hold memorial services.


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    © astron

    While we are waiting to start commissioning Apertif using the full field of view (i.e. using 39 all beams), we can test other important characteristics of the system to see whether they match the needs of the astronomers so that new and exciting science can be done.

    A key parameter is the stability of the spectral response of Apertif (the bandpass). This is of particular importance for the study of the gas in radio sources where we want to trace the presence of diffuse and faint neutral hydrogen that has extreme kinematics (i.e. very large outflow velocities). Such gas is one of the signatures of the feedback effects of the active super massive black hole on the rest of the galaxy.

    The good performance of the old WSRT system - where we could reach a level of 1/10000 in the stability of the bandpass - did allow to discover the existence of such gas, a finding completely unexpected and still not fully explained!

    Plans are to use Apertif to expand the heritage left by the WSRT and to search for many more cases of gas with extreme kinematics. Although test observations show that the present bandpass stability of Apertif is not quite yet at the level of the old WSRT, still the first results are showing that we are on the right track.

    The figure shows one of the radio galaxies (contours of the continuum emission on the left) and (on the right) the HI absorption observed with Apertif (black line). The Apertif data are superposed to the profile obtained years ago with the old MFFE receiver of the WSRT (red line).

    Despite the higher noise (due to the limitations of the present Apertif system), the shape of the absorption is well reproduced and a hint of the presence of gas with extreme kinematics (the blueshifted, shallow wing) is also appearing. This is very promising for the future Apertif surveys and, in particular for the Search for HI absorption with APERTIF (SHARP) project.


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    © ASTRON

    Understanding the life-cycle of radio loud AGN has recently gained a new broader relevance as it can help quantifying their feedback on the surrounding medium and on the overall galaxy evolution. Radio observations allow us to trace the different stages of this life-cycle.

    After having being fuelled by the central black hole for few tens of millions of years, jets in radio galaxies switch off. The following period is often referred to as the "remnant phase", during which particles are not accelerated anymore and the radio lobes start to fade away.

    Due to their very diffuse radio emission and low luminosity at frequencies above 1.4 GHz, these remnant sources have remained elusive for many years. Thanks to its unprecedented sensitivity and resolution at low frequencies LOFAR has opened the way to the study of these sources.

    As part of the ERC project RadioLife, we have performed an extensive search for remnant radio galaxies in the Lockman Hole, a well-studied extragalactic field. To select them we have used criteria based on both the source radio spectrum and their morphology. In this way we have identified 24 candidates which cover a variety of characteristics and likely represent different stages of the source evolution. In addition to this, we have run Monte-Carlo simulations to obtain mock catalogues of radio galaxies and predict the fraction of remnants that should be found in radio flux limited samples, such as the Lockman Hole sample.

    Our results show that, although even at low frequency the fraction of remnants remains low, we can make a more complete inventory of these objects, hence trace their evolution, something not possible before. These results suggest that a rapid expansion of the plasma must occur in the final stage of the life of a radio source. Simulations support this scenario. Interestingly, we find that not all remnants have ultra-steep spectrum as previously believed!

    Have a look at the complete results in the paper, which is now accepted for publication in Astronomy & Astrophysics ( https://arxiv.org/abs/1708.01904 ) and stay tuned for the next findings from the LoTSS survey!


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    © N. Lewandowska

    Numerous studies of pulsars have been carried out, especially at radio wavelengths, since their detection 50 years ago. The Crab pulsar was one of the first pulsars discovered. Interestingly, the discovery was made via its single radio pulses which were later labelled as Giant Pulses. In the following years the regular emission of the Crab pulsar at radio wavelengths and gamma-rays was also discovered. The recent discovery of pulsed emission at energies above 1.5 TeV has led to new theoretical approaches.

    However, there is still a lack of self consistent models for the emission of radio Giant Pulses. To constrain future modelling efforts, a number of multiwavelength studies have been carried out. These studies were limited due to small collection areas or high energy tresholds which represent an obstacle because of the steeply falling spectrum of the Crab pulsar. As an extension of previous studies we carried out simultaneous observations of Crab pulsar Giant Pulses with the Effelsberg radio telescope, the Westerbork Synthesis Radio Telescope and the Major Atmospheric Imaging Air Cherenkov telescopes and show the correlation analysis and corresponding results in this talk.

    About the image: Radio Giant pulses represent an enigmatic form of single pulse emission. They occur non-periodically, only at certain phase ranges, have much higher intensities than regular single pulses, reveal power law intensity distributions and very high brightness temperatures. Discovered in the case of the Crab pulsar, nowadays a small group of pulsars is known to emit radio giant pulses. Their emission mechanism is still not understood. The present figure shows radio giant pulses from the Crab pulsar observed with the Effelsberg radio telescope at a frequency of 1347 MHz. Each line represents one rotation of the pulsar. The peak which is visible in each line represents one radio giant pulse which occurred at the phase range of the Main pulse.


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    © Leonid Petrov

    It is not an exaggeration to say that the date September 15, 2016 split astrometry into two epochs: before and after Gaia.

    I will provide the overview of VLBI absolute astrometry programs in the last 3 years and describe the main result: the Radio Fundamental Catalogue (RFC) of 14,768 sources. Comparison of the RFC against Gaia DR1 showed a striking peculiarity: the directions of offsets of Gaia and VLBI positions of matching active galactic nuclei shows a strong anisotropy with a concentration along parsec-scale radio jet directions.

    I argue that the most probable explanation of such an anisotropy is the presence of optical structure at scales 1-200 mas, i.e. below the Gaia resolution.

    This discovery has a number of interesting observational consequences and has a profound impact on future VLBI astrometry programs. In some cases we will be able to reveal milliarcsecond-scale optical structure that cannot be studied directly with optical telescopes. We will be in a position to pinpoint in which area the optical flares occur: in the accretion disk, at the jet base (core) or at the hot spot on the extended jet.

    Future observational programs will be outlined.


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    © ASTRON

    Filippo Maccagni, the first student appointed under the ERC RadioLife grant to study the effect of the gas in the life of radio galaxies, has successfully defended his thesis at the University of Groningen last Monday (18 September).

    The title says it all: "Cold gas in the centre of radio-loud galaxies; New perspectives on triggering and feedback from HI absorption surveys and molecular gas"! It contains a number of very diverse studies on the connection between gas and AGN, using many different instruments and techniques, including the WSRT, ALMA and the VLT. Filippo has been very productive: the thesis includes four papers published in refereed journals and one about to be submitted. Particularly relevant is the work on the "last HI absorption survey with the 'old' Westerbork telescope" that he conducted in preparation for Apertif (see Daily Image of 30-05-2017).

    Filippo was supervised by Raffaella Morganti and Tom Oosterloo. The pdf of his thesis can be found here, but if you would like a proper paper copy, please ask!

    Filippo will now move to Cagliari, to work with an other ex-Groningen-ASTRON student, Paolo Serra. He will be part of the Fornax HI project with MeerKat, so he will continue to be involved with SKA Pathfinder radio telescopes.

    Congratulations Filippo!! Good luck with your new position and we hope to see you back soon to complete your work on the Apertif data!


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    © LBWG

    The Lofar Long-Baseline Working Group met at ASTRON from 11-15 September for a Busy Week. We have been developing algorithms and pipelines for the reduction of HBA international-baseline data, and concentrating particularly on pipelining data reduction in Surveys KSP fields. This should ultimately allow of the order of 100 sources to be detected and mapped in each field with noise levels of 0.1mJy.

    The reduction has been pipelined as far as the delay calibration, and we tested clock-TEC separation successfully; the top left hand part of the picture shows the derived TEC solutions as a function of time during a Surveys KSP observation. We also worked on a range of other problems including initial model generation for target fields, bright-source subtraction, pipeline efficiency, and automation of the target mapping/selfcal loops. An image of a source 30 arcmin away from a calibrator generated during the week is also shown (bottom right).

    Members of the LBWG attending the busy week (L to R in the photo): Alexander Drabent, Evita Vavilina, Gatis Gaigals, Carole Roskowinski, Rachael Ainsworth, Sean Mooney, Tim Shimwell, Leah Morabito, Neal Jackson, Alexander Kappes, Marco Iacobelli.


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    © Peter Maat and Roel Witvers

    This summer, four students from the University of Groningen spent three weeks at ASTRON, doing their summer school project as part of their RUG Honours Master programme. The four students: Luuk Boulogne, Robert Bwana, Max den Uijl and Daniel Yimam designed, constructed and tested an antenna array with four antennas, operating in the 50 MHz to 350 MHz frequency band. They were placed at ASTRONs test field in Dwingeloo. Analog optical links were used for the transfer of the antenna signals to Huisje West, where the signals were processed.

    The housing of the electronics, which was designed by the students, was printed using ASTRONs 3-D printer. The electronics were designed by Roel Witvers and assembled by the students. At the central location, Software-Defined Radio sticks and a computer were used as central processor. The processing software was generated by the students using the open source signal processing tool GNU Radio.

    The pictures: soldering of the electronics (top/left), tweaking with the cables at Huisje West (bottom/left), roll-out (top/right), one of the four antennas at the ASTRON test field (bottom/right).


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    © Harm-Jan Stiepel / CAMRAS

    Since 2009, the Dwingeloo Radiotelescope has been a national monument. That means that every year, the telescope is open at the national Open Monumentendag (which spans a weekend), along with many other monuments.

    This year, on 9/10 sept, the Open Monumentendag was extra special, because the national opening of the weekend took place in the municipality Westerveld. The radio telescope is one of the main monuments of the municipality - along with many other (mostly older) monuments.

    The telescope took a prominent place in the program of the opening of Open Monumentendag. A group of monument owners got a private tour of the telescope, as well as a lecture at Astron.

    Also special this year was that the former director's house, itself a municipal monument, was a part of the program. A slideshow was shown here, showing the history of the radio telescope; for kids a special show about "Kleine Reber" was shown.

    During the weekend, some 600 guests visited the telescope. Many volunteers of CAMRAS helped to make this possible; special thanks goes to Ard Hartsuijker who took the lead.


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    © Noelia Herrera

    Quantifying the fraction of AGN in the faint radio population is fundamental for studying galaxy evolution. A relatively easy and direct way to determine which galaxies do have a radio-active AGN is a detection using the Very Long Baseline Interferometry (VLBI) technique.

    We have observed ~3000 radio sources in the COSMOS extragalactic field with the Very Long Baseline Array (VLBA) at 1.4GHz to study the faint radio source population with statistically relevant numbers. We have detected 468 sources.

    The combination of number of sources, sensitivity, angular resolution and area covered by this project are unprecedented. In this overview I will present the survey design, observations, and calibration, along with the results of the project.


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