Are you the publisher? Claim or contact us about this channel


Embed this content in your HTML

Search

Report adult content:

click to rate:

Account: (login)

More Channels


Channel Catalog


Channel Description:

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

older | 1 | .... | 42 | 43 | (Page 44) | 45 | 46 | .... | 71 | newer

    0 0

    © ASTRON

    Some of the high-priority pointings of LOFAR have been on famous fields. These have the advantage to be well observed with many different telescopes covering many wavelength regions such as X-ray, optical, IR and a variety of radio frequencies. These ancillary data are essential for characterising the physical and evolutionary properties of the various source populations detected in deep radio fields (mainly star-forming galaxies and active galactic nuclei). One of these fields is the so called "Lockman Hole", first identified by Lockman et al. (1986) who noted the region has a very low column density of foreground Galactic HI, making it ideal for deep observations of extragalactic sources, particularly in the IR due to the low IR background. Since then, optical and infrared data have been taken using ground-based telescopes as well as the Spitzer and Herschel satellites. Also deep X-ray observations with XMM-Newton and Chandra are available for this piece of sky while most radio telescopes have also observed this region.

    The latest addition to this impressive collection is the image made with LOFAR. The LOFAR observations extend the multi-frequency radio information available for the Lockman Hole down to 60 MHz, allowing us to explore a new spectral window for the faint radio source population. The image shows a zoomed-in region approximately 2-degrees across at 150 MHz, a fraction of the full image which covers 34.7 square degrees. The image has a resolution of 18.6x14.7 arcsec and reaches an rms of 160 uJy/beam at the centre of the field. Work is in progress to further improve the quality and the resolution using facet calibration.

    As expected for a low-frequency selected sample, the vast majority of sources exhibit steep spectra, with a median spectral index of -0.78 between 150 MHz and 1.4 GHz. For a bright subset we can trace the spectral properties down to lower frequencies using 60-MHz LOFAR data, finding tentative evidence for sources to have flatter spectra between 60 and 150 MHz. We also identify a sample of 100 Ultra-steep spectrum (USS) sources and 13 peaked-spectrum sources. We estimate that up to 21 percent of these are candidate high-z radio galaxies, but further observations are required to confirm the physical nature of these objects.

    These results are presented in a paper accepted for publication in MNRAS including a number of ASTRON (and former-ASTRON) astronomers: Elizabeth Mahony, Raffaella Morganti, Ilse van Bemmel, Marisa Brienza, Jeremy Harwood and George Heald. http://adsabs.harvard.edu/abs/2016MNRAS.463.2997M


    0 0

    © ASTRON, NIKHEF

    After several experiments with different materials, the ASTRON instrument shop has successfully 3D-printed five parts of a 2x2 focus array for the Gridpix detector that is in development at NIKHEF.

    The parts consist of alternating layers of electrically conductive and non-conductive plastic. In this case the conductive element in the plastic is Carbon (black), while the other layers are regular plastic with any color you like. The idea is that the black bits can be electro-plated with copper.

    This is yet another step towards the use of 3D-printing for the cheap and environmentally-friendly manufacture of 3D electronics. For instance advanced antennas, or other systems that require the greater design freedom of 3 dimensions.

    It also shows that there are multiple layers of synergy between NWO institutes (e.g. NIKHEF and ASTRON).

    Jan Idserda (ASTRON), Rob Walet (NIKHEF)

    (Typical size of the focus block is 50 mm)


    0 0
  • 10/24/16--17:00: Horsehead Nebula
  • © Albert van Duin

    A recent Daily Image featured the Lynx Astrograph, designed and built by Rik ter Horst of ASTRON-NOVA. During the summer holidays I had the opportunity to do a night of imaging with this fast telescope under a dark sky in Burlage, Germany.

    It was a beautiful night, with very low humidity and a beautiful Milky Way overhead. At the end of this night in September, the familiar winter constellations were already starting to rise in the south-east. I couldn't resist making an image of the Horsehead Nebula in Orion, even though the sky was quickly getting brighter due to the appoaching dawn.

    Three integrations of 300s each were made @800ISO with a modified Canon 6D (CentralDS Astro-6D). The image shows the power of a fast (F/2.5) Astrograph and a modern digital single lens reflex camera.


    0 0

    © ASTRON

    The University of Stellenbosch (South Africa) has appointed our very own Stefan Wijnholds as Extraordinary(*) Associate Professor. The appointment letter states that "the University created this category of appointments to give recognition to individuals for their proven specialized expertise and / or eminence in their profession and field of study, and to involve them in the academic programmes of the relevant Department."

    Supported by travel funds from the EC FP7 MIDprep programme, Stefan has visited the research group of SKA Research Chair Prof. David B. Davidson in the Department of Electrical and Electronic Engineering several times over the last few years. His expertise in radio astronomical array signal processing and phased array system design proved to form a nice complement to the knowledge on antenna systems and electromagnetic modeling of the research group at the University of Stellenbosch. This led to constructive involvement of Stefan in a number of ongoing projects.

    This appointment formalizes this fruitful collaboration and will strengthen the ties between ASTRON and the University of Stellenbosch in the context of the SKA.

    (*) The term "extraordinary" here means "by special appointment", but it has a rather nicer ring to it.

    Editor's note: ASTRON is quietly proud of its track-record in nurturing more than its share of the bright young things who will design, build and operate the next generation of giant radio telescopes. Stefan is one of them, of course, as are Michiel Brentjes, Adam Deller, George Heald, Jason Hessels, Andre Offringa, V.N.Pandey, Oleg Smirnov, Bas van der Tol, Michael Wise, Sarod Yatawatta, and others...


    0 0

    © Spence et al., 2016, MNRAS, 459, L16

    There has been much speculation that AGN-driven outflows are an important process in galaxy evolution, regulating the shape of the high luminosity end of the galaxy luminosity function, and the correlations between black hole mass and host galaxy properties. However, the true energetic significance of the outflows has been hard to quantify. Here I present new results on the spatially resolved warm outflows in some of the most rapidly evolving galaxies in the local universe, which for the first time accurately quantify their masses and kinetic powers.

    The images show the the nearby ultra luminous infrared galaxy Mrk273 (z=0.0373) taken with the OSIRIS instrument on the 10m Gran Telescopio Canarias (GTC) on La Palma.

    The upper image was taken using a medium-band continuum filter centred at 5572A and shows the system of tidal tails which demonstrate that the system has been involved in a major galaxy merger that has triggered its starburst and AGN activity.

    The lower image was taken through a narrow-band filter centered on the redshifted Halpha emission line and shows a spectacular extended emission line nebulosity that extends out to a radius of 45kpc from the nucleus. There is currently a debate about the origin of such nebulosities: do they represent material that has been ejected from the nuclear regions by AGN-driven outflows, or rather tidal debris related to the merger events? See Spence et al., 2016, MNRAS, 459, L16 for further details.


    0 0

    © SKA

    The highly prestigious Jansky Lectureship has been awarded this year to our very own Jacqueline van Gorkom. She is one of the "golden crop" of uncommonly succesful Dutch female astronomers, which also includes Imke de Pater and Ewine van Dishoeck.

    Jacqueline received her Ph.D in astronomy from the Kapteyn Institute in Groningen, was a postdoc at the National Radio Astronomy Observatory, and worked at the Raman Research Institute in India and Princeton University before joining the faculty at Columbia in 1988. She currently is Rutherfurd Professor of Astronomy, and has served as Chair of the Department of Astronomy and Director of Graduate Studies.

    This is the 51st Jansky Lectureship, which is named in honor of Bell Labs antenna engineer Karl Jansky who first detected radio waves from a cosmic source (1932). Other recipients of the award include seven Nobel laureates (Subrahmanyan Chandrasekhar, Edward Purcell, Charles Townes, Arno Penzias, Robert Wilson, William Fowler, and Joseph Taylor) as well as Jocelyn Bell-Burnell, discoverer of the first pulsar, and Vera Rubin.

    The image shows Jacqueline, a giant among giants, as a member of the SKA Site Advisory Committee (SSAC, 2012): Ernie Seaquist (lower left), Wim Brouw, Tom Garvin, Jocelyn Bell Burnell, Peter Tindemans, Stefan Michalowski, Jim Moran, Ian Corbett, Jacqueline Van Gorkom, Jaap Baars, Jim Crocker, Subramaniam Ananthakrishnan, Roger Brissenden.

    Professor van Gorkom's awards include a National Science Foundation Faculty Award for Women, a Miller Visiting Professorship at the University of California, Berkeley, a Da Vinci Professorship at the Kapteyn Institute, and election as a Corresponding Member of the Royal Dutch Academy of Sciences. In addition, she has served on the visiting committees of the National Optical Astronomy Observatory and several radio observatories; on advisory committees for the VLA Upgrade Project; on the board of ASTRON, the Dutch National radio astronomy observatory; and on the site selection advisory committee for the Square Kilometre Array. She also has served on the scientific organizing committees of several astronomical symposia and on numerous proposal review boards for a variety of observatories and funding agencies.


    0 0

    © ASTRON

    Outdoor phased array antennas usually have a radome to protect the antenna. For large aperture arrays like the SKA Mid Frequency Aperture Array (MFAA) it is important to use cheap materials for the (many) radomes.

    The relevant electrical parameters of radome materials are the dielectric constant and the loss tangent. The measurement method uses a ring resonator. The setup is shown in the first picture. The screen on the network analyzer shows a typical measurement. Each peak corresponds with a resonance frequency. These resonance frequencies are directly related to the dielectric constant. The width of each peak is a measure for the losses of the material under test (a wider peak means more losses).

    The material under test is shown in the last picture. It is a biobased material that is measured within the framework of the BEETs project. The goal of this project is to investigate the use of biobased materials for high-end applications such as radomes. The partners in this project are Suikerunie, Philips Consumer Lifestyle, Rijksuniversiteit Groningen (RUG), the Aachen Maastricht Institute for Biobased Materials (AMIBM) and ASTRON. The project is funded by Samenwerkingsverband Noord-Nederland (SNN).


    0 0

    © ASTRON

    In 2013 SpaceNed (the Dutch association of space companies and institutes) started to collaborate with the Chinese Society of Astronautics (CSA). One of the members of SpaceNed and partner in the NCLE project, ISIS - Innovative Solutions in Space in Delft, participated in several SpaceNed - CSA bilateral meetings. On invitation of ISIS and SpacNed, a few members of CSA visited several companies and institutes in the Netherlands, including ASTRON. The ASTRON visit was planned for Wednesday, October 26th and it was a pleasure to welcome four CSA members from different entities of the China Aerospace Science and Technology Corporation.

    Michael Wise, Head of the Astronomy Group, informed our guests on ASTRON's mission and activities, our astronomy programme and current and near-future radio telecopes, including LOAR, Apertif and the SKA. And of course our activities aimed at establishing a regional science data centre for the SKA. In his presentation Albert-Jan Boonstra, Programme manager technical research and Scientific Director of the Dome project, highlighted the Research and Development activities of ASTRON. He also gave a short introduction on some of the large international projects ASTRON is involved in. Especially, the NCLE project aimed at developing a low-frequency receiver scientific payload for the Chinese Chang'e 4 mission drew their attention.

    Our guests enjoyed the tour through the R&D laboratory facilities, the tour at JIVE by Zsolt Paragi - Head of User Support, and the tour at the Dwingeloo telescope. In discussions on the comparative strengths of the scientific and technology programmes of both counties, parties agreed on the benefit of mutual scientific collaboration, and are looking forward to exploring possibilities for this. With new impressions our Chinese guests continued their trip for a visit to Airbus Defence and Space in Leiden.


    0 0

    © Phil Uttley

    Note that this colloquium announcement is one day early. We need tomorrow's AJDI slot for the retirement of Sjouke Zwier and Hans Tenkink

    The variable X-ray emission from accreting black holes encodes information about the structure and short-term evolution of the emitting regions closest to the black hole, but for many years it has been difficult to interpret these variations. Recent years have seen rapid developments in our understanding of the variability and what it tells us about the central regions, driven by a better understanding of how to use the combined energy and time information from X-ray data (so called 'spectral-timing') to understand the causal connections between the different emitting components. I will give a brief review of these exciting developments and a look forward to future advances with new X-ray missions.


    0 0

    © ASTRON/JIVE

    Today both Sjouke and Hans celebrate their retirement.

    Sjouke retires after working for ASTRON for 42 years. He has been involved in the development of state-of-the-art digital systems, managing to keep up with the rapidly evolving technology for decades! During his last years he participated in the development of UniBoard and UniBoard^2, very complex boards that increased the total data throughput of a single board to unmatched levels. On a personal level, Sjouke is very social and a man of his word. He is known by many as a good storyteller, with lots of humor and bizarre anecdotes. He was also a longstanding member of the celebrated ASTRON cabaret group, where he played his various roles with zest and panache.

    Hans has been a valued colleague in the ASTRON/JIVE family since August 1975. At ASTRON, he has served as an observer for the 25m Dwingeloo telescope, a data-reductie medewerker in Dwingeloo, and an observer at the WSRT in Westerbork. Hans transferred to JIVE in June 1999 as an operator, and rose to his current position of senior operator in March 2008. While at JIVE, Hans has experienced the transition from the ASIC-based EVN MkIV correlator to the EVN software correlator SFXC, as well as the introduction of operational real-time e-VLBI. In the latter, the operator in the Dwingeloo basement has some control over the equipment at participating telescopes around the world! In terms of local service, Hans has been on the BHV since its creation, and is on the bestuur of the PV.

    Editor's note: I will use my privileged position to mention two occasions where these guys really impressed me. Sjouke is a indefatigable ice-skater, who has finished the grueling 220km Elfstedentocht more than once. He was kind enough to tow me home one afternoon on the Tjonger, when I had fizzled out after a mere 50km. Hans demonstrated his broad grasp of science by winning the local competition of the Nationale Wetenschaps Quiz, ahead of local luminaries like Jaap Bregman.


    0 0

    © Ger de Bruyn

    It is well-known that LOFAR can image large areas of the sky. However, it is less known that this can be done at any resolution, up to the 0.25" PSF provided by the full European scale LOFAR in the HBA band. And this can be done using standard LOFAR tools!

    This animation cycles through a selection of 10 images of bright (1-10Jy) sources around the quasar 3C196, which is located in the middle of the image and marked as (SAP)000 (SAP is LOFAR jargon for Sub Array Pointing). The resolution in each VLBI image is about 700 times that of the overview panel which returns with a different objects at 3s intervals. Many of the radio sources exhibit the morphology of extragalactic double radio sources. Some show interesting complex structure (e.g. SAP007, 013) and some are barely resolved (e.g. SAP003, 015). The brightest compact sources can be used to transfer calibration solutions to even larger distance, "hopping" from one field to the next.

    The wonders of multi-beaming! I estimate that at least several hundred high resolution images can be extracted from a single 8h synthesis LOFAR observation. To display the full field of view at 0.25 arcsec resolution however, requires about 360,000 x 360,000 pixels of 0.1 x 0.1 arcsec. This adds up to 130 billion pixels, the equivalent of more than 16,000 4k x 2k monitors!!

    You want more technical details? Read on.

    Data: The data were taken as part of the LOFAR EoR project on 26 Feb 2016 with the aim to construct high resolution images for calibration. A record total of 74 stations participated: 12 IS, 14 RS and 48 CS; the observation lasted 8 hours. Digital beams were generated towards 20 bright sources in a 10x10 degrees area surrounding 3C196. For each pointing 4 groups of 6 contiguous 0.2 MHz subbands, centered around 116, 136, 156 and 171 MHz were correlated, each with 64ch/sb and 1 s time resolution.

    Calibration: Following the transfer of (self)calibration solutions for 3C196 to all other pointings, even those as far away as 4 degrees (like SAP012 and SAP016), each source could be self calibrated. I used an iterative scheme where the baseline range for calibration and imaging was slowly increased from 50 klambda to 900 klambda. In each iteration I used NDPPP to calibrate and WSClean to image and deconvolve.

    Some sources had only a peak flux of 30 mJy at the highest resolution. Depending on the time and frequency resolution of the data one can image an area of at least 1 degree diameter around every pointing, which means that basically the whole 10x10 degree field can be imaged at 0.25" resolution if you make an intelligent choice of sub array pointings and have plenty of disk space.

    Imaging: Note that the images have different scales and also saturate at different intensities (normally the peak intensity) which can be read off from the colour bar on the right. Typical off-source noise levels, in just 1.1 MHz of bandwidth (6 subbands), vary between 0.5 and 1.5 mJy depending on the peak brightness of the source; the dynamic range goes up to a few 1000:1 on the brightest sources. Most images refer to 171 MHz which of course has the highest resolution.


    0 0
  • 11/06/16--16:00: State visit to Australia
  • © ASTRON

    Their Majesties King Willem-Alexander and Queen�M�xima�visited Curtin University�on�1 November as part of a State visit to Australia. They�heard�about the Square Kilometre Array (SKA) project and the role of ASTRON, Curtin and other international partners, especially in the design of SKA-LOW. This was presented in the context of the close historical links between the Netherlands and Australia, which date back to the earliest radio observations of our Galaxy just after the Second World War.�

    The King and Queen viewed an SKA mini-station, a prototype of the antennas and electronics to be installed shortly in the Murchison region of Western Australia. They also met with Dutch and local researchers who work on the SKA at the Curtin Institute of Radio Astronomy and the International Centre for Radio Astronomy Research (ICRAR).

    The visit by the King and Queen to Western Australia coincides with the 400th anniversary of the landing of Dutch skipper Dirk�Hartog�on what is now known as Dirk�Hartog�Island.

    On the photo we see our own�Michiel�van Haarlem�and Peter Hall (Curtin University)�with the King and Queen in front of the SKA prototype station.�


    0 0
  • 11/07/16--16:00: There was a time...
  • © Rodjorna Retreat Sweden

    There was a time when our coffee and soup were dispensed by a diminiutive Philosopher with a warm smile and gleaming eyes. Aziz Thaleb was (and is) unusual in many ways (*), and it was a privilege to talk to him over a first cup of hot beverage before embarking on another day of ASTRON stuff.

    Such things do not last, of course, and eventually he moved on to open a retreat in Sweden, where he and his Annemiek now offer a variety of "energy-rich" zenactivities. He fondly remembers us all, and cordially invites us to check out his website:

    http://www.retraite-zweden.com/

    (*) Apart from his spiritual wealth, Aziz also happened to be the richest man in the building. Obviously, this is not too difficult in a scientific institute like ours, but it somehow put a special perspective on things.


    0 0

    © ASTRON

    On Friday October 28th at the TUDelft Raj Thilak Rajan successfully defended his PhD thesis with the title shown in the picture. His research addresses estimating the space-time kinematics of mobile nodes. Or in other words, how to find the relative distance and velocity of a network of moving sensors or transmitters while also estimating clock offsets and drifts at each of the nodes. Raj showed that this can be done in anchorless networks, networks without a-priori information on the absolute position or time of any node. This makes the approach a very useful bootstrapping method in conditions where absolute references are not available, such as remote or inaccessible locations.

    Application areas include indoor localization, underwater networks, drone swarms, and of course space-based satellite arrays. The latter topic was the focus of the ASTRON-TUDelft-UTwente OLFAR STW project, aiming at developing scalable autonomous nano satellite systems for low-frequency radio astronomy in space. Raj is the second OLFAR (ASTRON-TUDelft) PhD student graduating in this project. With the OLFAR work, together with R&D projects and studies such as DARIS, DEX, DSL, SURO etc, the community is gradually preparing technologies for a future low-frequency interferometric mission in space. The current Radboud-ASTRON-ISIS project NCLE aiming at providing a low-frequency science antenna payload for the Cahng'e 4 mission, is one of the next steps.


    0 0

    © Ross Burns

    Masers are really wonderful. Observing them with VLBI reveals information on range of scales from a few AU to a few kiloparsec, and all that in return for writing a single proposal. In this talk I'll cover the main projects which constituted my PhD - which centers on using maser VLBI to study the formation of massive stars, and the structure and kinematics of our Milky Way Galaxy.

    0 0

    © ASTRON

    The various projects in which the people of the ASTRON R&D department are involved require a lot: commitment, enthusiasm, flexibility, thinking out of the box, and of course hard work. But it is easy to overlook that they also rely on the quiet support of the R&D secretaries in a broad way. The aim of Monique, Patricia, Renate and Ina is to offer a high-level service. To achieve this, they collaborate with each other as much as possible: they share action lists and mailboxes, which enables them to smoothly take over certain tasks from each other when necessary.

    To mention a few things they are taking care of:

    - making appointments;

    - organizing meeting and events;

    - ordering catering;

    - booking accommodation in and around Dwingeloo;

    - making travel arrangements.

    Furthermore, the R&D secretaries assist in project and/or commercial activities, and facilitate in the development of new intranet webforms like the travel requests and publication list. They also keep an eye on the various processes and actions of the Competence Group Leaders (and the Head of the R&D department) and write drafts for letters, parts of proposals, presentations, R&D website, emails, newsletters, etc.

    Maybe it is less visible what they do, but it is certainly not less valuable. In the background they take care of many things, which is highly appreciated. That's why they should be considered as the quiet force behind a successful and hard-working R&D department.

    Editor's note: That's the spirit! Too few Leaders realize that this ASTRON/JIVE/NOVA/DOME family chronicle is a great (and low-cost) vehicle for motivating the devoted people that make them possible. Who is next?


    0 0

    © VIRAC

    The European VLBI Network (EVN) Consortium Board of Directors (CBD) met on 25 October 2016 in Irbene (Latvia). The Chairman (who is Rene Vermeulen of ASTRON) recalled the recent CBD decision taken by electronic consultation to welcome VIRAC (Ventspils International Radio Astronomy Centre) as a full member of the EVN; this was confirmed with round of applause.

    The CBD heard about the latest technical progress, and the successful participation of the Irbene 32-meter telescope in recent EVN sessions at several frequencies. After lunch, the CBD was given a comprehensive guided tour in, on and around the telescope (top image). General admiration was expressed for the remarkable achievements of the VIRAC team, assisted by EVN friends from many places, in refurbishing this Soviet-vintage facility. The eventful day also included a pleasant dinner in Ventspils, and finally an interesting “no-low-gears” bus ride back to the hotel in Jurmala (where the Executive session was held the next morning).

    A brief ceremony and press conference was held on 26 October 2016 in Riga, in the presence of Ms. Diana Laipniece [apparently no relative of Gottfried Wilhelm (von) Leibni(t)z], representing the Latvian Ministry of Science and Education. The importance of the EVN milestone for VIRAC was explained, and linked to the wider growth of the scientific and technological capacity of Latvia. Rene Vermeulen, as Chair of the EVN CBD, and Dr. Karlis Kreslins, Acting Rector of the Ventspils University College to which VIRAC belongs, signed a document confirming VIRAC's accession to the EVN (bottom image). A second crucial part of the event, involving several other participants, was preparing for a conclusion to be reached on 15 November; this will no doubt be reported in another AJDI soon. Finally, the event at the ministry was an important opportunity to draw attention to the ongoing EC-Twinning project "BALTICS", in which ASTRON and the University of Manchester provide training for VIRAC staff, focused on LOFAR and eMERLIN technology and science. Indeed, VIRAC is striving to acquire funding to build and operate a LOFAR station and become a member of the ILT; we fervently hope for success in that endeavour.


    0 0

    © J.B.R. Oonk

    The Low Frequency Array (LOFAR), thanks to its high spectral resolution, enables studies of the low-frequency universe not only in continuum, but also through spectral lines. In the context of the LOFAR Cassiopeia A Spectral Survey (LCASS), led by ASTRON astronomer R. Oonk, we are exploring the low frequency spectrum. In particular we use radio recombination lines (RRL) to determine the physical conditions (i.e. temperature and density) of cool, diffuse clouds. The main tracer of these clouds is the HI 21 cm line, but it is known to be difficult to obtain the physical conditions of the gas from this line. Low-frequency RRLs provide an important, complementary method.

    We have used the LOFAR Low Band Antennas (LBA) to perform a systematic high spectral resolution (0.4 kHz) investigation of the low-frequency 30-80 MHz spectrum along the line of sight to the famous supernova remnant Cassiopeia A (Cas A). We complemented the LOFAR observations with a 300-390 MHz Westerbork Synthesis Radio telescope observation (WSRT). In the first paper, of a planned series, we focus on the RRLs from carbon and hydrogen. We detect carbon RRLs (CRRL) in absorption with LOFAR and in emission with WSRT. Hydrogen RRLs (HRRL) are detected with WSRT. This is only the second time that the very weak HRRL lines have been detected in these clouds, and the WSRT measurement is the lowest frequency detection to date.

    The RRLs towards Cas A are known to arise in cold clouds in the Perseus spiral arm at -47 and -38 km/s. The deep LOFAR and WSRT observations provide us with high signal to noise detections over a large range in frequency. Measuring the frequency behaviour of RRLs is crucial and enables a detailed study of the gas conditions. We analyze the line optical depths and widths with our new RRL models (Salgado et al. 2016). These models provide the first physically consistent fit to all the available data and show that the CRRL clouds in the Perseus arm are best fit with an electron temperature 85 K and an electron density 0.04 cm^-3. The uncertainty on the temperature and density is less than 15%.

    Based on these results we argue that much of these CRRLs likely arise in the CO-dark surface layers of molecular clouds where most of the carbon is ionized but hydrogen has made the transition from atomic to molecular. Recent surveys and simulations show that about half of the diffuse, molecular ISM may reside in this CO dark phase. The CO-dark gas is difficult to observe directly and LOFAR may thus provide us with a new, powerful tracer of this phase. More detailed studies of the CRRL emitting gas and its relation with CO-dark and cool atomic gas are underway (Salas et al. in prep.). The results shown here have been accepted for publication in MNRAS (Oonk et al.) and can also be found here, http://adsabs.harvard.edu/abs/2016arXiv160906857O

    Figure: (Left) Overlay of the WSRT (blue) and LOFAR LBA (black) CRRL spectra for the line of sight to Cas A. The LBA spectrum has been inverted for this comparison and the WSRT spectrum was re-scaled to match the peak of the -47 km/s cloud in the LBA spectrum. There is a good match between the two indicating that all of the CRRL emitting gas is situated in front of the remnant. The weak line feature at 0 km/s is associated with the Orion spur. (Right) CRRL optical depth models overlaid on the measurements for the -47 km/s cloud. Our LOFAR and WSRT data is shown in black. In addition we show literature measurements in blue (Kantharia et al. 1998 and Payne et al. 1989). The optical depth is plotted as a function of quantum number n, where increasing n equals lower frequencies. The red curve shows the best-fit model (85 K and 0.04 cm^-3). In addition we show more models for the same best-fit temperature, but with a 25 percent difference in the density (dot-dash: 0.03 cm^-3 and dashed: 0.05 cm^-3). The large changes in the models with density (and temperature) highlight the strength of CRRLs in determining the physical conditions of the gas.


    0 0

    © Andrey Timokhin

    Note that this colloquium is on wednesday (today)!

    Discovered five decades ago, radio pulsars - rapidly rotating highly magnetized neutron stars - are still one of the mysteries of modern astrophysics. We are sure that pulsar emission is generated in the magnetosphere, but we still do not know exactly how nor where.

    However, over the recent decade we have made significant progress toward creating a self-consistent model of pulsar magnetospheres, which is the necessary step in the quest for understanding pulsar emission mechanism(s).

    In this talk I will give an overview of this decades-old problem, and describe recent advances in modeling of pulsar magnetospheres.


    0 0
  • 11/16/16--16:00: The voice of...
  • © Hans van der Marel / Albert van Duin

    On 1 November the head of the R&D department, Gert Kruithof, organised an activity for the people from his department, which would be both "entertaining and educative".

    So, in the afternoon everybody gathered in the auditorium and Gert introduced the speaker and instructor for the afternoon: Liselotte Hambeukers from Stemkunst. Liselotte is a speech therapist (logopedist) and she also studied professional classical singer at the conservatorium of Maastricht. To combine these two professions, she started her own company Stemkunst, which gives training in the use of the voice, in speech and in presenting. For this day the focus was on the voice.

    Liselotte started her presentation by explaining that when people are talking with each other, only a small fraction (7%) of the communication is happening by means of words. About half of the communication is by attitude, expression and gestures, and the remaining 40% is on behalf of the voice. She explained that the way we are speaking, the sound and use of the voice and our accents, have a big impact on how other people assess us, especially if they do not see us. This was illustrated by some short movies. In a voice we can distinguish expressive versus thoroughness, and powerful versus subdued. Liselotte showed several examples after which we had to indicate where in the quadrant we would place this person.

    After the break it was time for some more activity. The group was split into two parts and one group was instructed by Liselotte and the other group by her colleague, Berbke Hermans. At first we had to do some exercises to condition our body and voice. And then we got instruction on the use of our voice and our attitude. And, of course, this had to be practised.

    Altogether, it was an interesting afternoon. And if you think that somebody is talking in a more authorative way than he or she used to do, or raises the hands to receive applause, like Sjouke Zwier did after his retirement speech, that is the result of this afternoon.

    The very instructive and entertaining afternoon was finished with a tasteful (and tasty) Chinese buffet in the canteen.


older | 1 | .... | 42 | 43 | (Page 44) | 45 | 46 | .... | 71 | newer