Onsala Space Observatory

Onsala, Sweden

Onsala Space Observatory

Onsala, Sweden

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News Article | December 21, 2016
Site: www.eurekalert.org

ALMA observes radio waves from the Universe, at the low-energy end of the electromagnetic spectrum. With the newly installed Band 5 receivers, ALMA has now opened its eyes to a whole new section of this radio spectrum, creating exciting new observational possibilities. The European ALMA Programme Scientist, Leonardo Testi, explains the significance: "The new receivers will make it much easier to detect water, a prerequisite for life as we know it, in our Solar System and in more distant regions of our galaxy and beyond. They will also allow ALMA to search for ionised carbon in the primordial Universe." It is ALMA's unique location, 5000 metres up on the barren Chajnantor plateau in Chile, that makes such an observation possible in the first place. As water is also present in Earth's atmosphere, observatories in less elevated and less arid environments have much more difficulty identifying the origin of the emission coming from space. ALMA's great sensitivity and high angular resolution mean that even faint signals of water in the local Universe can now be imaged at this wavelength [1]. The Band 5 receiver, which was developed by the Group for Advanced Receiver Development (GARD at Onsala Space Observatory, Chalmers University of Technology, Sweden, has already been tested at the APEX telescope in the SEPIA instrument. These observations were also vital to help select suitable targets for the first receiver tests with ALMA. The first production receivers were built and delivered to ALMA in the first half of 2015 by a consortium consisting of the Netherlands Research School for Astronomy (NOVA) and GARD in partnership with the National Radio Astronomy Observatory (NRAO, which contributed the local oscillator to the project. The receivers are now installed and being prepared for use by the community of astronomers. To test the newly installed receivers observations were made of several objects including the colliding galaxies Arp 220, a massive region of star formation close to the centre of the Milky Way, and also a dusty red supergiant star approaching the supernova explosion that will end its life [2]. To process the data and check its quality, astronomers, along with technical specialists from ESO and the European ALMA Regional Centre (ARC) network, gathered at the Onsala Space Observatory in Sweden, for a "Band 5 Busy Week" hosted by the Nordic ARC node [3] (http://www. ). The final results have just been made freely available to the astronomical community worldwide. Team member Robert Laing at ESO is optimistic about the prospects for ALMA Band 5 observations: "It's very exciting to see these first results from ALMA Band 5 using a limited set of antennas. In the future, the high sensitivity and angular resolution of the full ALMA array will allow us to make detailed studies of water in a wide range of objects including forming and evolved stars, the interstellar medium and regions close to supermassive black holes." [1] A key spectral signature of water lies in this expanded range -- at a wavelength of 1.64 millimetres. [2] The observations were performed and made possible by the ALMA Extension of Capabilities team in Chile. [3] The ESO Band 5 Science Verification team includes: Elizabeth Humphreys, Tony Mroczkowski, Robert Laing, Katharina Immer, Hau-Yu (Baobab) Liu, Andy Biggs, Gianni Marconi and Leonardo Testi. The team working on processing the data included: Tobia Carozzi, Simon Casey, Sabine König, Ana Lopez-Sepulcre, Matthias Maercker, Iván Martí-Vidal, Lydia Moser, Sebastien Muller, Anita Richards, Daniel Tafoya and Wouter Vlemmings. The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of ESO, the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI). ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA. ESO is the foremost intergovernmental astronomy organisation in Europe and the world's most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world's most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world's largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become "the world's biggest eye on the sky".


News Article | December 21, 2016
Site: phys.org

The European ALMA Programme Scientist, Leonardo Testi, explains the significance: "The new receivers will make it much easier to detect water, a prerequisite for life as we know it, in our Solar System and in more distant regions of our galaxy and beyond. They will also allow ALMA to search for ionised carbon in the primordial Universe." It is ALMA's unique location, 5000 metres up on the barren Chajnantor plateau in Chile, that makes such an observation possible in the first place. As water is also present in Earth's atmosphere, observatories in less elevated and less arid environments have much more difficulty identifying the origin of the emission coming from space. ALMA's great sensitivity and high angular resolution mean that even faint signals of water in the local Universe can now be imaged at this wavelength. The Band 5 receiver, which was developed by the Group for Advanced Receiver Development (GARD at Onsala Space Observatory, Chalmers University of Technology, Sweden, has already been tested at the APEX telescope in the SEPIA instrument. These observations were also vital to help select suitable targets for the first receiver tests with ALMA. The first production receivers were built and delivered to ALMA in the first half of 2015 by a consortium consisting of the Netherlands Research School for Astronomy (NOVA) and GARD in partnership with the National Radio Astronomy Observatory (NRAO, which contributed the local oscillator to the project. The receivers are now installed and being prepared for use by the community of astronomers. To test the newly installed receivers observations were made of several objects including the colliding galaxies Arp 220, a massive region of star formation close to the centre of the Milky Way, and also a dusty red supergiant star approaching the supernova explosion that will end its life. To process the data and check its quality, astronomers, along with technical specialists from ESO and the European ALMA Regional Centre (ARC) network, gathered at the Onsala Space Observatory in Sweden, for a "Band 5 Busy Week" hosted by the Nordic ARC node (http://www.nordic-alma.se/). The final results have just been made freely available to the astronomical community worldwide. Team member Robert Laing at ESO is optimistic about the prospects for ALMA Band 5 observations: "It's very exciting to see these first results from ALMA Band 5 using a limited set of antennas. In the future, the high sensitivity and angular resolution of the full ALMA array will allow us to make detailed studies of water in a wide range of objects including forming and evolved stars, the interstellar medium and regions close to supermassive black holes." Explore further: First observations from SEPIA: New APEX instrument for finding water in the universe


Sakamoto K.,Academia Sinica, Taiwan | Aalto S.,Onsala Space Observatory | Evans A.S.,University of Virginia | Evans A.S.,U.S. National Radio Astronomy Observatory | And 2 more authors.
Astrophysical Journal Letters | Year: 2010

Infrared pumping and its effect on the excitation of HCN molecules can be important when using rotational lines of HCN to probe dense molecular gas in galaxy nuclei. We report the first extragalactic d tection of (sub)millimeter otational lines of vibrationally excited HCN, in the dust-enshrouded nucleus of the luminous infrared galaxy GC 4418. We estimate the excitation temperature of Tvib ≈ 230 K between the vibrational ground and excited (v 2 = 1) states. This excitation is most likely due to infrared radiation. At this high vibrational temperature the path through the v 2 = 1 state must have a strong impact on the rotational excitation in the vibrational ground level, although it may not be dominant for all rotational levels. Our observations also revealed nearly confusion-limited lines of CO, HCN, HCO+, H13CN, HC15N, CS, N 2H+, and HC3N at λ ∼ 1 mm. Their relative intensities may also be affected by the infrared pumping. 2010. The American Astronomical Society. All rights reserved. Printed in the U.S.A.


News Article | December 13, 2015
Site: www.sciencenews.org

Reports of large, previously unknown planets wandering through the outer solar system have been exaggerated. A few odd blips of radio waves from space hint at not one but two massive bodies far beyond the orbit of Neptune, researchers suggest in two papers posted online December 9 on arXiv.org. A dearth of follow-up observations and the sheer unlikelihood of stumbling across such beasts, however, are cause for a healthy dose of skepticism. “The nature of the source [of these radio waves] has only become more confusing,” admits Wouter Vlemmings, an astronomer at Chalmers University of Technology and Onsala Space Observatory in Sweden and lead author of one of the papers. Based on feedback received less than 24 hours after posting the papers, “I would rule the chance for an outer solar system object extremely small,” he says. “It was just not something we could rule out on the data alone.” Vlemmings and colleagues noticed one of the alleged interlopers zipping by W Aql, a star located about 1,290 light-years away in the constellation Aquila. A point of light darted across two images taken in March and April with the Atacama Large Millimeter/submillimeter Array, or ALMA, a collection of radio telescopes in northern Chile. By May, it was gone. There were a few potential culprits. It could have been one moving object. Or the radio blasts could have come from two stationary objects, such as distant galaxies. Catching two coincidental galactic flares in the same narrow field of view is highly unlikely, though, the researchers say. The source was also moving too fast to be a star hurtling through the Milky Way. Assuming the object was real, that left the possibility that it was either a large planet less than 600 billion kilometers from the sun or a large icy body meandering between the orbits of Saturn and Uranus. A second team, led by René Liseau, also at Chalmers University, noticed another wandering dot when ALMA was pointed at a different part of the sky. That team was looking for exoplanets around the triple star system Alpha Centauri, which at 4.2 light-years away, are the closest stars to the sun. Once in July 2014 and again in May 2015, the researchers saw a speck of radio energy moving along with Alpha Centauri. They reasoned that they caught a chance alignment with one of three possible objects: an icy body beyond the edge of the Kuiper belt, a planet a couple of times as wide as Earth and around 45 billion kilometers away or a brown dwarf 3 trillion kilometers away — 20,000 times as far from the sun as Earth. In both cases, the teams report only two observations, which means it’s premature to assume that either detection is one moving object. “Anything could create two random detections, and you can always fit a straight line through any two points,” says Scott Sheppard, a planetary scientist at the Carnegie Institution for Science in Washington, D.C. Researchers typically wait until they’ve seen something three times before reporting a new member of the solar system. “If they actually had three detections that all fit the same movement pattern,” Sheppard says, “then I would think it was interesting.” A large hidden member of the solar system is not a crazy idea. The solar system is still largely unexplored and there are plenty of places to hide a distant rocky planet. Odd patterns seen in the orbits of icy bodies past the Kuiper belt hint at such a world orbiting several hundred times as far from the sun as Earth (SN: 11/29/14, p. 18), but researchers have yet to find anything definitive. By posting the findings online, “we were soliciting feedback to avoid publishing something obviously wrong,” Vlemmings says. They’ve already learned that the mystery object by W Aql would have shown up in data from the WISE mission, a space-based telescope that mapped the infrared glow of the entire sky in 2010 and 2011. Data from that mission have previously ruled out a planet the size of Saturn within about 4.2 trillion kilometers of the sun and a planet the size of Jupiter nearly three times as far away. Still, Vlemmings says that he and his colleagues will sift through more-recent ALMA data to see if the object shows up a third time. A ninth planet or dim star looping around the sun would be an extraordinary discovery, but it’s going to require some extraordinary evidence first.


News Article | December 13, 2015
Site: www.sciencenews.org

Reports of large, previously unknown planets wandering through the outer solar system have been exaggerated. A few odd blips of radio waves from space hint at not one but two massive bodies far beyond the orbit of Neptune, researchers suggest in two papers posted online December 9 on arXiv.org. A dearth of follow-up observations and the sheer unlikelihood of stumbling across such beasts, however, are cause for a healthy dose of skepticism. “The nature of the source [of these radio waves] has only become more confusing,” admits Wouter Vlemmings, an astronomer at Chalmers University of Technology and Onsala Space Observatory in Sweden and lead author of one of the papers. Based on feedback received less than 24 hours after posting the papers, “I would rule the chance for an outer solar system object extremely small,” he says. “It was just not something we could rule out on the data alone.” Vlemmings and colleagues noticed one of the alleged interlopers zipping by W Aql, a star located about 1,290 light-years away in the constellation Aquila. A point of light darted across two images taken in March and April with the Atacama Large Millimeter/submillimeter Array, or ALMA, a collection of radio telescopes in northern Chile. By May, it was gone. There were a few potential culprits. It could have been one moving object. Or the radio blasts could have come from two stationary objects, such as distant galaxies. Catching two coincidental galactic flares in the same narrow field of view is highly unlikely, though, the researchers say. The source was also moving too fast to be a star hurtling through the Milky Way. Assuming the object was real, that left the possibility that it was either a large planet less than 600 billion kilometers from the sun or a large icy body meandering between the orbits of Saturn and Uranus. A second team, led by René Liseau, also at Chalmers University, noticed another wandering dot when ALMA was pointed at a different part of the sky. That team was looking for exoplanets around the triple star system Alpha Centauri, which at 4.2 light-years away, are the closest stars to the sun. Once in July 2014 and again in May 2015, the researchers saw a speck of radio energy moving along with Alpha Centauri. They reasoned that they caught a chance alignment with one of three possible objects: an icy body beyond the edge of the Kuiper belt, a planet a couple of times as wide as Earth and around 45 billion kilometers away or a brown dwarf 3 trillion kilometers away — 20,000 times as far from the sun as Earth. In both cases, the teams report only two observations, which means it’s premature to assume that either detection is one moving object. “Anything could create two random detections, and you can always fit a straight line through any two points,” says Scott Sheppard, a planetary scientist at the Carnegie Institution for Science in Washington, D.C. Researchers typically wait until they’ve seen something three times before reporting a new member of the solar system. “If they actually had three detections that all fit the same movement pattern,” Sheppard says, “then I would think it was interesting.” A large hidden member of the solar system is not a crazy idea. The solar system is still largely unexplored and there are plenty of places to hide a distant rocky planet. Odd patterns seen in the orbits of icy bodies past the Kuiper belt hint at such a world orbiting several hundred times as far from the sun as Earth (SN: 11/29/14, p. 18), but researchers have yet to find anything definitive. By posting the findings online, “we were soliciting feedback to avoid publishing something obviously wrong,” Vlemmings says. They’ve already learned that the mystery object by W Aql would have shown up in data from the WISE mission, a space-based telescope that mapped the infrared glow of the entire sky in 2010 and 2011. Data from that mission have previously ruled out a planet the size of Saturn within about 4.2 trillion kilometers of the sun and a planet the size of Jupiter nearly three times as far away. Still, Vlemmings says that he and his colleagues will sift through more-recent ALMA data to see if the object shows up a third time. A ninth planet or dim star looping around the sun would be an extraordinary discovery, but it’s going to require some extraordinary evidence first.


News Article | December 11, 2015
Site: www.sciencenews.org

Reports of large, previously unknown planets wandering through the outer solar system have been exaggerated. A few odd blips of radio waves from space hint at not one but two massive bodies far beyond the orbit of Neptune, researchers suggest in two papers posted online December 9 on arXiv.org. A dearth of follow-up observations and the sheer unlikelihood of stumbling across such beasts, however, are cause for a healthy dose of skepticism. “The nature of the source [of these radio waves] has only become more confusing,” admits Wouter Vlemmings, an astronomer at Chalmers University of Technology and Onsala Space Observatory in Sweden and lead author of one of the papers. Based on feedback received less than 24 hours after posting the papers, “I would rule the chance for an outer solar system object extremely small,” he says. “It was just not something we could rule out on the data alone.” Vlemmings and colleagues noticed one of the alleged interlopers zipping by W Aql, a star located about 1,290 light-years away in the constellation Aquila. A point of light darted across two images taken in March and April with the Atacama Large Millimeter/submillimeter Array, or ALMA, a collection of radio telescopes in northern Chile. By May, it was gone. There were a few potential culprits. It could have been one moving object. Or the radio blasts could have come from two stationary objects, such as distant galaxies. Catching two coincidental galactic flares in the same narrow field of view is highly unlikely, though, the researchers say. The source was also moving too fast to be a star hurtling through the Milky Way. Assuming the object was real, that left the possibility that it was either a large planet less than 600 billion kilometers from the sun or a large icy body meandering between the orbits of Saturn and Uranus. A second team, led by René Liseau, also at Chalmers University, noticed another wandering dot when ALMA was pointed at a different part of the sky. That team was looking for exoplanets around the triple star system Alpha Centauri, which at 4.2 light-years away, are the closest stars to the sun. Once in July 2014 and again in May 2015, the researchers saw a speck of radio energy moving along with Alpha Centauri. They reasoned that they caught a chance alignment with one of three possible objects: an icy body beyond the edge of the Kuiper belt, a planet a couple of times as wide as Earth and around 45 billion kilometers away or a brown dwarf 3 trillion kilometers away — 20,000 times as far from the sun as Earth. In both cases, the teams report only two observations, which means it’s premature to assume that either detection is one moving object. “Anything could create two random detections, and you can always fit a straight line through any two points,” says Scott Sheppard, a planetary scientist at the Carnegie Institution for Science in Washington, D.C. Researchers typically wait until they’ve seen something three times before reporting a new member of the solar system. “If they actually had three detections that all fit the same movement pattern,” Sheppard says, “then I would think it was interesting.” A large hidden member of the solar system is not a crazy idea. The solar system is still largely unexplored and there are plenty of places to hide a distant rocky planet. Odd patterns seen in the orbits of icy bodies past the Kuiper belt hint at such a world orbiting several hundred times as far from the sun as Earth (SN: 11/29/14, p. 18), but researchers have yet to find anything definitive. By posting the findings online, “we were soliciting feedback to avoid publishing something obviously wrong,” Vlemmings says. They’ve already learned that the mystery object by W Aql would have shown up in data from the WISE mission, a space-based telescope that mapped the infrared glow of the entire sky in 2010 and 2011. Data from that mission have previously ruled out a planet the size of Saturn within about 4.2 trillion kilometers of the sun and a planet the size of Jupiter nearly three times as far away. Still, Vlemmings says that he and his colleagues will sift through more-recent ALMA data to see if the object shows up a third time. A ninth planet or dim star looping around the sun would be an extraordinary discovery, but it’s going to require some extraordinary evidence first.


News Article | February 15, 2017
Site: phys.org

The Onsala Twin Telescopes are two identical dish antennas, each 13.2 metres in diameter. They are part of an international initiative involving 20 countries, aimed at increasing our knowledge about the Earth and its movements. The telescopes detect radio waves from brilliant but distant galaxies that act like fixed stars in the sky. By continually measuring the positions on the sky of bright radio galaxies, the telescopes in the network can determine their own location in space. John Conway is professor in observational radio astronomy at Chalmers and director of Onsala Space Observatory. "The sources that the telescopes measure are distant galaxies, each of which has at its centre a supermassive black hole whose surroundings shine brightly when the black hole consumes material. This is applied astronomy at its best" he says. The Onsala Twin Telescopes are part of a growing international network of similar telescopes. As part of the global project VGOS (VLBI Global Observing System), they have company all over the world. Measurements of this kind have been carried out over the last few decades, and Onsala's 20-metre telescope has participated in these. But with a dedicated network of telescopes, observations can now be carried out 24 hours a day, all year round, and will be able to able to make measurements ten times as precise as is possible today. "With the new network we will be able to measure distances between telescopes to millimetre precision, and almost in real time", says Rüdiger Haas, professor of space geodesy at Chalmers. Onsala's history of geodetic measurements is a long one. In 1964, the observatory's iconic 25-metre radio telescope became the first in Europe to take part in geodetic VLBI (very long baseline interferometry). The observatory's 20-metre telescope, inaugurated in 1976, boasts geodetic measurements over a longer period than any other telescope in the world. The new telescopes and their network meet global needs, as expressed in a resolution which was adopted by the General Assembly of the United Nations in February 2015. The resolution, A Global Geodetic Reference Frame for Sustainable Development, recognised for the first time the importance of coordinating geodetic measurements on a global scale. The resolution strengthened exisiting work in the UN initiative Global Geospatial Information Management (UN-GGIM) and with the Global Geodetic Reference Frame (GGRF). "Future research on sustainable development and on the Earth as a system will require more reliable, long-term, high-precision measurements. The Onsala Twin Telescopes are a natural continuation of our already long history of such measurements in Onsala", says Gunnar Elgered, professor of electrical measurements and head of the Department of Earth and Space Science at Chalmers. Similar telescopes are already in place in the United States, in Hawaii and Maryland, in Wettzell in Germany, in Yebes in Spain, on Santa Maria in the Azores, and on the Arctic Svalbard islands. New telescopes are planned for other locations, among them South Africa and Finland. Operations for the complete network of 16 or more stations are expected to start in 2020. A reference system with this level of precision is also needed for many applications in Earth Sciences. It will become possible, for example, to measure sea level relative to the centre of the Earth, in order to test models for climate change. Data from the network will also be able to contribute to many other exciting areas of science, for example the movement of Earth's tectonic plates, the Earth's changing rotation and axial tilt. The construction and installation of the Onsala Twin Telescopes has been funded by a generous grant from the Knut and Alice Wallenberg Foundation and Chalmers University of Technology. Explore further: Black holes provide us with knowledge of the Earth


Ramstedt S.,University of Bonn | Montez R.,Rochester Institute of Technology | Kastner J.,Rochester Institute of Technology | Vlemmings W.H.T.,Onsala Space Observatory
Astronomy and Astrophysics | Year: 2012

Context. Magnetic fields have been measured around asymptotic giant branch (AGB) stars of all chemical types using maser polarization observations. If present, a large-scale magnetic field would lead to X-ray emission, which should be observable using current X-ray observatories. Aims. The aim is to search the archival data for AGB stars that are intrinsic X-ray emitters. Methods. We have searched the ROSAT, CXO, and XMM-Newton archives for serendipitous X-ray observations of a sample of ∼500 AGB stars. We specifically searched for the AGB stars detected with GALEX. The data is calibrated, analyzed and the X-ray luminosities and temperatures are estimated as functions of the circumstellar absorption. Results. We identify 13 AGB stars as having either serendipitous or targeted observations in the X-ray data archives, however for a majority of the sources the detailed analysis show that the detections are questionable. Two new sources are detected by ROSAT: T Dra and R UMa. The spectral analysis suggests that the emission associated with these sources could be due to coronal activity or interaction across a binary system. Conclusions. Further observations of the detected sources are necessary to clearly determine the origin of the X-ray emission. Moreover, additional objects should be subject to targeted X-ray observations in order to achieve better constraints for the magnetic fields around AGB stars. © 2012 ESO.


Carozzi T.D.,University of Glasgow | Carozzi T.D.,Onsala Space Observatory | Woan G.,University of Glasgow
IEEE Transactions on Antennas and Propagation | Year: 2011

Many modern radio applications, such as astronomy and remote sensing, require high-precision polarimetry. These applications put exacting demands on radio polarimeters (antenna systems that can measure the state of polarization of radio sources), and in order to assess their polarimetric performance, a figure of merit (FoM) would be desirable. Unfortunately, we find that the parameter commonly used for this purpose, the cross-polarization ratio, is not suitable as a polarimetry FoM unless it is given in an appropriate coordinate system. This is because although the cross-polarization ratio is relevant for raw, uncalibrated polarimetry, in general it is not relevant to the quality of the polarimetry after polarimetric calibration. However, a cross-polarization ratio can be constructed from invariants of the Jones matrix (the matrix that describes the polarimetric response of a polarimeter) that quantifies polarimetric performance even after calibration. We call this cross-polarization ratio the intrinsic cross-polarization ratio (IXR) and conclude that it is a fundamental FoM for polarimeters. We then extend the IXR concept from the Jones calculus to the Mueller calculus and also to interferometers, and we give numerical examples of these parameters applied to the Parkes radio telescope, the Westerbork synthesis radio telescope, and the Effelsberg telescope. © 2011 IEEE.


Struve C.,Onsala Space Observatory | Conway J.E.,Onsala Space Observatory
Astronomy and Astrophysics | Year: 2012

We present Very Long Baseline Array (VLBA) Hi absorption observations of the core regions of the powerful radio galaxies 3C 236 and 4C 31.04. Broad absorption (?v ? 350 km s?1) straddling the systemic velocity is detected in both sources, in each case concentrated on one side of the radio core. We argue that the observations are consistent with the presence of Hi absorbing disks with r ? 900 pc and r ? 200 pc in 3C 236 and 4C 31.04 respectively - although given the limited spatial coverage of the HI absorption other interpretations cannot be ruled out. The spatially resolved absorption detected against the counter-jet of 3C 236 shows a velocity gradient with an amplitude and direction supporting a rotating disk model; in contrast only a tentative velocity gradient is seen in the 4C 31.04 data set.While on larger scales both radio galaxies show evidence for interaction and merging we find no direct evidence in either source that cold gas is in-falling onto the radio core. In 3C 236 we instead find against the core blue-shifted absorption that might be part of the fast outflow of neutral gas detected in more sensitive (but lower spatial resolution) observations. Along the main jet of 3C 236 we find clumps of high opacity Hi absorption concentrated to one side of the jet.We speculate that these Hi clumps may be interacting with the jet, potentially even being the cause of the misalignment of the eastern jet between kiloparsec and megaparsec scales. In addition to its broad absorption 4C 31.04 shows a narrow absorption component (FWHM = 23 km s?1) redshifted relative to the galaxy systemic velocity by 115 km s?1. This feature may be a residual sign of a recent accretion/merging event, however the absorbing gas cloud must be located 100 pc from the core. © ESO 2012.

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