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  • richardmitnick 7:53 pm on April 18, 2014 Permalink | Reply
    Tags: , , , , , ESO VLTI   

    From ESO: “Double Engine for a Nebula” 2009 


    European Southern Observatory

    5 August 2009
    Contacts

    Florentin Millour
    Max-Planck Institute for Radio Astronomy
    Bonn, Germany
    Tel: +49 228 525 188
    Email: fmillour@mpifr.de

    Henri Boffin
    ESO
    Paranal, Chile
    Tel: +49 89 3200 6222
    Email: hboffin@eso.org

    Valeria Foncea
    ESO
    Chile
    Tel: +56 2 463 3123
    Email: vfoncea@eso.org

    ESO has just [2009] released a stunning new image of a field of stars towards the constellation of Carina (the Keel). This striking view is ablaze with a flurry of stars of all colours and brightnesses, some of which are seen against a backdrop of clouds of dust and gas. One unusual star in the middle, HD 87643, has been extensively studied with several ESO telescopes, including the Very Large Telescope Interferometer (VLTI). Surrounded by a complex, extended nebula that is the result of previous violent ejections, the star has been shown to have a companion. Interactions in this double [binary star] system, surrounded by a dusty disc, may be the engine fuelling the star’s remarkable nebula.

    ds

    ESO VLT Interferometer
    ESO VLTI

    The new image, showing a very rich field of stars towards the Carina arm of the Milky Way, is centred on the star HD 87643, a member of the exotic class of B[e] stars. It is part of a set of observations that provide astronomers with the best ever picture of a B[e] star.

    mw
    Observed structure of the Milky Way’s spiral arms.

    The [above star field] image was obtained with the Wide Field Imager (WFI) attached to the MPG/ESO 2.2-metre telescope at the 2400-metre-high La Silla Observatory in Chile. The image shows beautifully the extended nebula of gas and dust that reflects the light from the star. The central star’s wind appears to have shaped the nebula, leaving bright, ragged tendrils of gas and dust. A careful investigation of these features seems to indicate that there are regular ejections of matter from the star every 15 to 50 years.

    ESO Wide Field Imager 2.2m LaSilla
    WFI on 2.2m telescope

    ESO 2.2 meter telescope
    2.2m telescope at LaSilla

    ESO LaSilla
    ESO at LaSilla

    A team of astronomers, led by Florentin Millour, has studied the star HD 87643 in great detail, using several of ESO’s telescopes. Apart from the WFI, the team also used ESO’s Very Large Telescope (VLT) at Paranal.

    At the VLT, the astronomers used the NACO adaptive optics instrument, allowing them to obtain an image of the star free from the blurring effect of the atmosphere. To probe the object further, the team then obtained an image with the Very Large Telescope Interferometer (VLTI)[above].

    ESO NACO
    NACO on ESO/VLT

    The sheer range of this set of observations, from the panoramic WFI image to the fine detail of the VLTI observations, corresponds to a zoom-in factor of 60 000 between the two extremes. The astronomers found that HD 87643 has a companion located at about 50 times the Earth–Sun distance and is embedded in a compact dust shell. The two stars probably orbit each other in a period between 20 and 50 years. A dusty disc may also be surrounding the two stars.

    The presence of the companion could be an explanation for the regular ejection of matter from the star and the formation of the nebula: as the companion moves on a highly elliptical orbit, it would regularly come very close to HD 87643, triggering an ejection.

    The work on HD 87643 has been published in a paper to appear in Astronomy and Astrophysics: A binary engine fueling HD 87643’s complex circumstellar environment using AMBER/VLTI imaging, by F. Millour et al.

    See the full article, with notes, here.

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  • richardmitnick 8:16 am on April 15, 2014 Permalink | Reply
    Tags: , , , , ESO VLTI   

    From ESO: “Sharpest views of Betelgeuse reveal how supergiant stars lose mass” 2009 


    European Southern Observatory

    29 July 2009
    Contacts

    Pierre Kervella
    Observatoire de Paris-Meudon
    Paris, France
    Tel: +33 1 45 07 79 66
    Email: Pierre.Kervella@obspm.fr

    Keiichi Ohnaka
    Max-Planck Institute for Radio Astronomy
    Bonn, Germany
    Tel: +33 1 45 07 79 66
    Email: kohnaka@mpifr-bonn.mpg.de

    Olivier Hainaut
    ESO
    Garching, Germany
    Tel: +49 89 3200 6752
    Email: ohainaut@eso.org

    Using different state-of-the-art techniques on ESO’s Very Large Telescope, two independent teams of astronomers have obtained the sharpest ever views of the supergiant star Betelgeuse. They show that the star has a vast plume of gas almost as large as our Solar System and a gigantic bubble boiling on its surface. These discoveries provide important clues to help explain how these mammoths shed material at such a tremendous rate.

    bet

    Betelgeuse — the second brightest star in the constellation of Orion (the Hunter) — is a red supergiant, one of the biggest stars known, and almost 1000 times larger than our Sun. It is also one of the most luminous stars known, emitting more light than 100000 Suns. Such extreme properties foretell the demise of a short-lived stellar king. With an age of only a few million years, Betelgeuse is already nearing the end of its life and is soon doomed to explode as a supernova. When it does, the supernova should be seen easily from Earth, even in broad daylight.

    Red supergiants still hold several unsolved mysteries. One of them is just how these behemoths shed such tremendous quantities of material — about the mass of the Sun — in only 10 000 years. Two teams of astronomers have used ESO’s Very Large Telescope (VLT) and the most advanced technologies to take a closer look at the gigantic star. Their combined work suggests that an answer to the long-open mass-loss question may well be at hand.

    ESO VLT
    VLT

    The first team used the adaptive optics instrument, NACO, combined with a so-called “lucky imaging” technique, to obtain the sharpest ever image of Betelgeuse, even with Earth’s turbulent, image-distorting atmosphere in the way. With lucky imaging, only the very sharpest exposures are chosen and then combined to form an image much sharper than a single, longer exposure would be.

    ESO NACO
    NACO on VLT

    The resulting NACO images almost reach the theoretical limit of sharpness attainable for an 8-metre telescope. The resolution is as fine as 37 milliarcseconds, which is roughly the size of a tennis ball on the International Space Station (ISS), as seen from the ground.

    “Thanks to these outstanding images, we have detected a large plume of gas extending into space from the surface of Betelgeuse,” says Pierre Kervella from the Paris Observatory, who led the team. The plume extends to at least six times the diameter of the star, corresponding to the distance between the Sun and Neptune.

    “This is a clear indication that the whole outer shell of the star is not shedding matter evenly in all directions,” adds Kervella. Two mechanisms could explain this asymmetry. One assumes that the mass loss occurs above the polar caps of the giant star, possibly because of its rotation. The other possibility is that such a plume is generated above large-scale gas motions inside the star, known as convection — similar to the circulation of water heated in a pot.

    To arrive at a solution, astronomers needed to probe the behemoth in still finer detail. To do this Keiichi Ohnaka from the Max Planck Institute for Radio Astronomy in Bonn, Germany, and his colleagues used interferometry. With the AMBER instrument on ESO’s Very Large Telescope Interferometer, which combines the light from three 1.8-metre Auxiliary Telescopes of the VLT, the astronomers obtained observations as sharp as those of a giant, virtual 48-metre telescope. With such superb resolution, the astronomers were able to detect indirectly details four times finer still than the amazing NACO images had already allowed (in other words, the size of a marble on the ISS, as seen from the ground).

    ESO VLT Interferometer

    ESO AMBER
    AMBER

    “Our AMBER observations are the sharpest observations of any kind ever made of Betelgeuse. Moreover, we detected how the gas is moving in different areas of Betelgeuse’s surface ― the first time this has been done for a star other than the Sun”, says Ohnaka.

    The AMBER observations revealed that the gas in Betelgeuse’s atmosphere is moving vigorously up and down, and that these bubbles are as large as the supergiant star itself. Their unrivalled observations have led the astronomers to propose that these large-scale gas motions roiling under Betelgeuse’s red surface are behind the ejection of the massive plume into space.

    This research was presented in two papers to appear in Astronomy and Astrophysics:
    The close circumstellar environment of Betelgeuse: Adaptive optics spectro-imaging in the near-IR with VLT/NACO, by Pierre Kervella et al., and Spatially resolving the inhomogeneous structure of the dynamical atmosphere of Betelgeuse with VLTI/AMBER, by Keiichi Ohnaka et al.

    The teams are composed of P. Kervella, G. Perrin, S. Lacour, and X. Haubois (LESIA, Observatoire de Paris, France), T. Verhoelst (K. U. Leuven, Belgium), S. T. Ridgway (National Optical Astronomy Observatories, USA), and J. Cami (University of Western Ontario, Canada), and of K. Ohnaka, K.-H. Hofmann, T. Driebe, F. Millour, D. Schertl, and G. Weigelt (Max-Planck-Institute for Radio Astronomy, Bonn, Germany), M. Benisty (INAF-Osservatorio Astrofisico di Arcetri, Firenze, Italy), A. Chelli (LAOG, Grenoble, France), R. Petrov and F. Vakili (Lab. H. Fizeau, OCA, Nice, France), and Ph. Stee (Lab. H. Fizeau, OCA, Grasse, France).

    See the full article, with notes, here.

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  • richardmitnick 8:30 am on March 12, 2014 Permalink | Reply
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    From ESO: “VLT Spots Largest Yellow Hypergiant Star” 


    European Southern Observatory

    12 March 2014
    Mix of new and old observations reveals exotic binary system

    Contacts

    Olivier Chesneau
    Laboratoire Lagrange / Univ. Nice Sophia-Antipolis, CNRS – Observatoire de la Côte d’Azur
    Nice, France
    Tel: +33 (0)4 92 00 19 79
    Email: olivier.chesneau@oca.eu

    Richard Hook
    ESO, Public Information Officer
    Garching bei München, Germany
    Tel: +49 89 3200 6655
    Cell: +49 151 1537 3591
    Email: rhook@eso.org

    ESO’s Very Large Telescope Interferometer has revealed the largest yellow star — and one of the ten largest stars found so far. This hypergiant has been found to measure more than 1300 times the diameter of the Sun, and to be part of a double [binary] star system, with the second component so close that it is in contact with the main star. Observations spanning over sixty years, some from amateur observers, also indicate that this rare and remarkable object is changing very rapidly and has been caught during a very brief phase of its life.

    star

    Using ESO’s Very Large Telescope Interferometer (VLTI), Olivier Chesneau (Observatoire de la Côte d’Azur, Nice, France) and an international team of collaborators have found that the yellow hypergiant star HR 5171 A is absolutely huge — 1300 times the diameter of the Sun and much bigger than was expected. This makes it the largest yellow star known. It is also in the top ten of the largest stars known — 50% larger than the famous red supergiant Betelgeuse — and about one million times brighter than the Sun.

    “The new observations also showed that this star has a very close binary partner, which was a real surprise,” says Chesneau. “The two stars are so close that they touch and the whole system resembles a gigantic peanut.”

    The astronomers made use of a technique called interferometry to combine the light collected from multiple individual telescopes, effectively creating a giant telescope up to 140 metres in size. The new results prompted the team to thoroughly investigate older observations of the star spanning more than sixty years, to see how it had behaved in the past.

    Yellow hypergiants are very rare, with only a dozen or so known in our galaxy — the best-known example being Rho Cassiopeiae. They are among the biggest and brightest stars known and are at a stage of their lives when they are unstable and changing rapidly. Due to this instability, yellow hypergiants also expel material outwards, forming a large, extended atmosphere around the star.

    Despite its great distance of nearly 12 000 light-years from Earth, the object can just about be seen with the naked eye by the keen-sighted. HR 5171 A has been found to be getting bigger over the last 40 years, cooling as it grows, and its evolution has now been caught in action. Only a few stars are caught in this very brief phase, where they undergo a dramatic change in temperature as they rapidly evolve.

    By analysing data on the star’s varying brightness, using observations from other observatories, the astronomers confirmed the object to be an eclipsing binary system where the smaller component passes in front and behind the larger one as it orbits. In this case HR 5171 A is orbited by its companion star every 1300 days. The smaller companion is only slightly hotter than HR 5171 A’s surface temperature of 5000 degrees Celsius.

    Chesneau concludes “The companion we have found is very significant as it can have an influence on the fate of HR 5171 A, for example, stripping off its outer layers and modifying its evolution.”

    This new discovery highlights the importance of studying these huge and short-lived yellow hypergiants, and could provide a means of understanding the evolutionary processes of massive stars in general.

    vlti

    See the full article, with notes, here.

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  • richardmitnick 4:07 pm on February 26, 2014 Permalink | Reply
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    From ESO: “Feeding the Monster” 2005 


    European Southern Observatory

    New VLT Images Reveal the Surroundings of a Super-massive Black Hole

    17 October 2005
    Almudena Prieto
    Max-Planck Institute for Astronomy
    Heidelberg, Germany
    Tel: +34 67 702 66 57
    Email: prieto@mpia.de

    Near-infrared images of the active galaxy NGC 1097, obtained with the NACO adaptive optics instrument on ESO’s Very Large Telescope, disclose with unprecedented detail a complex central network of filamentary structure spiralling down to the centre of the galaxy. These observations provide astronomers with new insights on how super-massive black holes lurking inside galaxies get fed.

    centre
    The Centre of the Active Galaxy NGC 1097

    ESO VLT
    VLT

    ESO NACO
    NACO

    Another view of NGC 1097
    ngc
    Credit: ESO, Telescope: UT3/Melipal at VLT, Instrument: VIMOS

    ESO VIMOS
    VIMOS

    “This is possibly the first time that a detailed view of the channelling process of matter, from the main part of the galaxy down to the very end in the nucleus is released,” says Almudena Prieto (Max-Planck Institute, Heidelberg, Germany), lead author of the paper describing these results.

    Located at a distance of about 45 million light-years in the southern constellation Fornax (the Furnace), NGC 1097 is a relatively bright, barred spiral galaxy seen face-on. At magnitude 9.5, and thus just 25 times fainter than the faintest object that can be seen with the unaided eye, it appears in small telescopes as a bright, circular disc.

    NGC 1097 is a very moderate example of an Active Galactic Nucleus (AGN), whose emission is thought to arise from matter (gas and stars) falling into oblivion in a central black hole. However, NGC 1097 possesses a comparatively faint nucleus only, and the black hole in its centre must be on a very strict “diet”: only a small amount of gas and stars is apparently being swallowed by the black hole at any given moment.

    Astronomers have been trying to understand for a long time how the matter is “gulped” down towards the black hole. Watching directly the feeding process requires very high spatial resolution at the centre of galaxies. This can be achieved by means of interferometry as was done with the VLTI MIDI instrument on the central parts of another AGN, NGC 1068, or with adaptive optics.

    ESO VLTI
    ESO VLTI

    ESO VLTI MIDI
    ESO VLTI MIDI

    Thus, astronomers obtained images of NGC 1097 with the adaptive optics NACO instrument attached to Yepun, the fourth Unit Telescope of ESO’s VLT. These new images probe with unprecedented detail the presence and extent of material in the very proximity of the nucleus. The resolution achieved with the images is about 0.15 arcsecond, corresponding to about 30 light-years across. For comparison, this is only 8 times the distance between the Sun and its nearest star, Proxima Centauri.

    As can be seen in last year’s image, NGC 1097 has a very strong bar and a prominent star-forming ring inside it. Interior to the ring, a secondary bar crosses the nucleus almost perpendicular to the primary bar. The newly released NACO near-infrared images show in addition more than 300 star-forming regions, a factor four larger than previously known from Hubble Space Telescope images. These “HII regions” can be seen as white spots in the photo. At the centre of the ring, a moderate active nucleus is located. Details from the nucleus and its immediate surroundings are however outshone by the overwhelming stellar light of the galaxy seen as the bright diffuse emission all over the image.

    The astronomers therefore applied a masking technique that allowed them to suppress the stellar light. This unveils a bright nucleus at the centre, but mostly a complex central network of filamentary structures spiralling down to the centre.

    “Our analysis of the VLT/NACO images of NGC 1097 shows that these filaments end up at the very centre of the galaxy”, says co-author Juha Reunanen from ESO.

    “This network closely resembles those seen in computer models”, adds co-worker Witold Maciejewski from the University of Oxford, UK. “The nuclear filaments revealed in the NACO images are the tracers of cold dust and gas being channelled towards the centre to eventually ignite the AGN.”

    The astronomers also note that the curling of the spiral pattern in the innermost 300 light-years seem indeed to confirm the presence of a super-massive black hole in the centre of NGC 1097. Such a black hole in the centre of a galaxy causes the nuclear spiral to wind up as it approaches the centre, while in its absence the spiral would be unwinding as it moves closer to the centre.

    An image of NGC 1097 and its small companion, NGC 1097A, was taken in December 2004, in the presence of Chilean President Lagos with the VIMOS instrument on ESO’s Very Large Telescope (VLT).

    See the full article with notes, here.

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  • richardmitnick 7:32 am on October 1, 2013 Permalink | Reply
    Tags: , , , , ESO VLTI   

    From ESO: “The star T Leporis as seen with VLTI” 


    European Southern Observatory

    lep
    ESO/J.-B. Le Bouquin et al.
    Release date: 18 February 2009

    This image from ESO’s Very Large Telescope Interferometer is one of the sharpest colour images ever made. It shows the Mira-like star T Leporis in great detail. The central disc is the surface of the star, which is surrounded by a spherical shell of molecular material expelled from the star. In order to appreciate the feat of such measurement, one should realize that the star appears, on the sky, as small as a two-storey house on the Moon. The resolution of the image is about 4 milli-arcseconds.
    In this image, obtained by combining hundreds of interferometric measurements, the blue channel includes infrared light from 1.4 to 1.6 micrometres, the green, from 1.6 to 1.75 micrometres, and the red, from 1.75 to 1.9 micrometres. In the green channel, the molecular envelope is thinner, and appears as a thin ring around the star.

    See the full article here.

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