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  • richardmitnick 9:38 pm on August 22, 2014 Permalink | Reply
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    From NAOJ Subaru: “Umbrella Galaxy’s Merger Models the Cosmic Food Chain” 

    NAOJ

    NAOJ

    July 1, 2014

    Scientists have used the Subaru Telescope and the W. M. Keck Observatory to study the Umbrella Galaxy (NGC 4651), a twin of the Milky Way Galaxy, and to accurately model how it is swallowing a smaller galaxy. Their findings reveal insights into galactic behavior and contribute to a better understanding of how structure forms in the Universe.

    Keck Observatory
    Keck Observatory Interior
    Keck

    ngc4651
    Figure: The Umbrella Galaxy takes its name from a mysterious feature seen on the left here, that is now found to be debris from a tiny galaxy, only a 50th its size, shredded apart by gravity. The image is a combination of data from the 0.5 m BlackBird Remote Observatory Telescope and Suprime-Cam on the 8 m Subaru Telescope. (Credit: R. Jay GaBany)

    The Umbrella Galaxy, named for the umbrella-shaped structure extending from its disk, is about 62 million light-years away from Earth in the northern constellation of Coma Berenices. Its faint parasol is composed of a stellar stream, thought to be the remnants of a smaller galaxy being pulled apart by the large galaxy’s intense gravitational field, which may eventually absorb this small galaxy completely.

    Although small galaxies often merge into larger ones throughout the Universe, it has been difficult to provide three-dimensional details of how such mergers proceed, because the shredded galaxies are so faint. Observations with the Subaru Prime Focus Camera (Suprime-Cam) and Keck Observatory’s Deep Imaging and Multi-Object Spectrograph (DEIMOS) have enabled a team of astronomers, led by Caroline Foster (Australian Astronomical Observatory), to identify enough details of the Umbrella Galaxy’s merger to provide a specific model of how and when it occurred. Suprime-Cam captured panoramic images of the Umbrella Galaxy, and then DEIMOS, installed on the Keck II telescope, mapped out the motions of the stream, which allowed scientists to determine how the galaxy is being shredded.

    Because the stars in the stream are extremely faint, the scientists used a proxy technique to measure the speeds of brighter objects moving along with the stream stars. These bright “tracers” include globular star clusters, planetary nebulae (i.e., bright clouds of glowing gas and dust surrounding highly evolved stars), and patches of glowing hydrogen gas.

    Co-author Aaron Romanowsky (San José State University and University of California Observatories) summed up the significance of the research: “This is important because our whole concept about what galaxies are and how they grow has not been fully verified. We think they are constantly consuming smaller galaxies as part of a cosmic food chain, all pulled together by a mysterious form of invisible ‘dark matter’. When a galaxy is torn apart, we sometimes get a glimpse of the hidden vista because the stripping process lights it up. That’s what occurred here.”

    Foster highlighted the importance of innovative instrumentation of telescopes such as the Subaru Telescope and Keck Observatory in uncovering processes that govern the Universe: “Through new techniques we have been able to measure the movements of the stars in the very distant, very faint, stellar stream in the Umbrella. This allows us, for the first time, to reconstruct the history of the system.” Romanowsky added, “Being able to study streams this far away means that we can reconstruct the assembly histories of many more galaxies. That means that we can get a handle on how often these ‘minor mergers’ — thought to be an important way that galaxies grow — actually occur. We can also map out the orbits of the stellar streams to test the pull of gravity for exotic effects, much like the Moon going around the Earth, but without having to wait 300 million years for the orbit to complete.”

    Note:

    This article is based on a press release from Keck Observatory, posted on June 30, 2014.

    Reference to the research paper:

    C. Foster, Lux, H., Romanowsky, A.J., Martínez-Delgado, D., Zibetti, S., Arnold, J.A., Brodie, J.P., Ciardullo, R., GaBany, R.J., Merrifield, M.R., Singh, N., and Strader, J. Kinematics and simulations of the stellar stream in the halo of the Umbrella Galaxy, to appear in Monthly Notices of the Royal Astronomical Society, 2014.

    See the full article here.

    The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

    In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

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    NAOJ Subaru Telescope interior
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    NAOJ Okayama Astrophysical Observatory Telescope
    Okayama Astrophysical Observatory

    The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

    In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

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  • richardmitnick 9:17 pm on August 22, 2014 Permalink | Reply
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    From NAOJ Subaru: “Direct Imaging of a Super-Jupiter Around a Massive Star” 2012 

    NAOJ

    NAOJ

    November 19, 2012

    An international team of astronomers, led by Joseph Carson (College of Charleston and Max Planck Institute for Astronomy), has discovered a “super-Jupiter” orbiting the massive star Kappa Andromedae. Using the High Contrast Instrument for the Subaru Next Generation Adaptive Optics (HiCIAO) and the Infrared Camera and Spectrograph (IRCS) mounted on the Subaru Telescope, the team was able to directly image the new exoplanet, a gas giant with a mass about 13 times that of Jupiter and an orbit somewhat larger than Neptune’s. The host star has a mass 2.5 times that of the Sun, making it the highest mass star to ever host a directly imaged planet or very low-mass brown dwarf.

    Successful direct imaging of an exoplanet is difficult at best, because the brightness of the central star obscures the fainter light emitted from a planet orbiting it. A major goal of the SEEDS Project (Note), of which the current team is a part, is to explore hundreds of nearby stars in an effort to directly image extrasolar planets and protoplanetary/debris disks. The team used Subaru Telescope’s high-contrast imaging instrument, HiCIAO, with the AO 188 Adaptive Optics System to hunt for exoplanets. They targeted many young high-mass stars and then concentrated follow-up observations on the relatively young star Kappa Andromedae. Located 170 light years from our own Solar System, Kappa Andromedae is a member of the Columba stellar moving group, with a youthful estimated age of 30 million years (compared with the Sun’s older age of about 5 billion years). Young star systems are attractive targets for directly imaging planets because young planets retain significant heat from their formation, thus enhancing their brightness at infrared wavelengths.

    Kappa And b, a so-called “super-Jupiter” (a gas giant significantly more massive than Jupiter), was detected in independent observations in January and July 2012 at four different wavelengths. Comparison of its relative positions between the two time periods revealed that Kappa And b exhibits “common proper motion” with the host star, proving that the two objects are gravitationally bound. A comparison of Kappa And b’s brightness between the four different wavelengths revealed infrared colors similar to those of a handful of other gas giant planets successfully imaged around stars.

    two
    Figure: Left (a): A false-color, near-infrared (1.2 – 2.4 microns) image of the Kappa And system. Image processing removed the light from the host star, which lies behind the mask (a software-generated, dark disk) at the center of the square. The colored speckles represent starlight left over after removal of light from the host star. Separated by about 55 Astronomical Units from its host star, the super-Jupiter, Kappa And b (upper left), resides at a distance about 1.8 times greater than Neptune’s orbital separation from the Sun. (Credit: NAOJ)
    Right (b): A “signal-to-noise ratio map” generated from the image to the left. The colored speckles represent residual light that remains after subtraction of light from the host star. The white feature toward the upper left, representing a high signal-to-noise value, indicates detection of the super-Jupiter with high confidence. (Credit: NAOJ)

    Such direct imaging of an extrasolar planet is exceptionally rare, especially for objects with orbital separations akin to the planets in our own Solar System. In a single infrared snapshot, the glare of the host star completely overwhelms the tiny point of light that is Kappa And b. The SEEDS observing team distinguished its distinct light only after using a technique known as angular differential imaging, which combines a time-series of individual images in a manner that allows for removal of the otherwise overwhelming glare of the host star from the final, combined image.

    The large masses of the host star and its gas giant planet sharply contrast to objects in our own Solar System. In recent years some observers and theoreticians have argued that large stars like Kappa Andromedae are likely to have large planets, perhaps conforming to a simple scaled-up model of our own Solar System. Other experts suggest that there are limits to extrapolating from our own Solar System; if a star is too massive, its powerful radiation may disrupt the “normal” planet formation process that would otherwise occur in the disk surrounding a star, its circumstellar disk. The discovery of the super-Jupiter around Kappa Andromedae demonstrates that stars as large as 2.5 solar masses are still fully capable of producing planets within their circumstellar disks.

    The SEEDS research team is continuing to study the light emitted from Kappa And b across a broad wavelength range in order to better understand the atmospheric chemistry of the gas giant and define its the orbital characteristics. The team also continues to explore the system for possible secondary planets, which may have influenced the formation of Kappa And b and its orbital evolution. These follow-up studies will yield further clues not only about the formation of the Super-Jupiter but also about principles of planet formation around massive stars.

    References:
    The paper describing the research leading to this discovery, Direct Imaging Discovery of a ‘Super-Jupiter’ Around the Late B-Type Star κ And, has been accepted for publication in the Astrophysical Journal Letters.

    Core members of the research team are:

    J. Carson, College of Charleston, USA and Max Planck Institute for Astronomy, Germany
    C. Thalmann, University of Amsterdam, The Netherlands and Max Planck Institute for Astronomy, Germany
    M. Janson, Princeton University, USA
    T. Kozakis, College of Charleston, USA
    M. Bonnefoy, Max Planck Institute for Astronomy, Germany
    B. Biller, Max Planck Institute for Astronomy, Germany
    J. Schlieder, Max Planck Institute for Astronomy, Germany
    T. Currie, University of Toronto, Canada
    M. McElwain, Goddard Space Flight Center, USA
    M. Goto, Ludwig Maximilians University, Germany
    T. Henning, Max Planck Institute for Astronomy, Germany
    W. Brandner, Max Planck Institute for Astronomy, Germany
    M. Feldt, Max Planck Institute for Astronomy, Germany
    R. Kandori, National Astronomical Observatory of Japan, Japan
    M. Kuzuhara, National Astronomical Observatory of Japan and University of Tokyo, Japan
    H. Tamura, National Astronomical Observatory of Japan, Japan

    Acknowledgements:
    This research was made possible in part by support from the U.S. National Science Foundation.

    Note:

    The SEEDS Project began in 2009 for a five-year period using 120 observing nights at Subaru Telescope, located at the summit of Mauna Kea on the island of Hawaii. Principal investigator Motohide Tamura (National Astronomical Observatory of Japan) leads the SEEDS survey.

    See the full article here.

    The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

    In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

    NAOJ Subaru Telescope

    NAOJ Subaru Telescope interior
    Subaru

    ALMA Array
    ALMA

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    Solar Flare Telescope

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    Nobeyama Radio Observatory

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    Nobeyama Radio Observatory: Solar

    Misuzawa Station Japan
    Mizusawa VERA Observatory

    NAOJ Okayama Astrophysical Observatory Telescope
    Okayama Astrophysical Observatory

    The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

    In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

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  • richardmitnick 8:53 pm on August 21, 2014 Permalink | Reply
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    From NAOJ Subaru: “A Chemical Signature of First-Generation Very-Massive Stars” 

    NAOJ

    NAOJ

    A team of astronomers from the National Astronomical Observatory of Japan (NAOJ), the Konan University and the University of Hyogo in Japan, the University of Notre Dame, and New Mexico State University (Note 1) has used the 8.2 m Subaru Telescope’s High Dispersion Spectrograph (HDS) to discover a low-mass star, SDSS J0018-0939 (Fig. 1), that exhibits the peculiar chemical abundance ratios associated with the process of creating new atomic nuclei (nucleosynthesis) in a first-generation very-massive star. Until now, no observational evidence has supported numerical simulations of the existence of very-massive stars among the first generation of stars formed after the Big Bang.

    image 1
    Figure 1: An optical image of the star SDSS J0018-0939, obtained by the Sloan Digital Sky Survey. This is a low-mass star with a mass about half that of the Sun; the distance to this star is about 1000 light years; its location in the sky is close to the constellation Cetus. (Credit: SDSS/NAOJ)

    Sloan Digital Sky Survey Telescope
    Sloan Digital Sky Survey Telescope

    The Importance of the Mass of First-Generation Stars

    First-generation stars are objects formed in the early Universe (within a few hundred million years after the Big Bang) from gas clouds containing only hydrogen and helium (Fig. 4). First-generation stars are the probable precursors of the formation of the Universe’s structure and chemical enrichment; large stellar systems, e.g., galaxies, formed later.

    Numerical simulations have made significant progress in understanding the formation of the first stars (Note 2). Recent simulations suggest that a small fraction of very-massive stars with masses exceeding one hundred times that of the Sun could have formed in the early Universe, even though the large majority of first stars formed with masses of ten to a hundred times that of the Sun. Their strong UV radiation and energetic explosions are likely to have had a significant impact on the evolution of stellar systems.

    Signatures of First Stars Recorded by Low-Mass Milky-Way Stars

    Supernova explosions ejected elements formed by the first massive stars and dispersed them into the gas that formed the next generations of stars (Fig. 5).

    Stars with masses slightly less than the Sun’s have very long lifetimes, long enough that they are still shining. The Milky Way contains such low-mass stars with low overall metal content, including the elements produced by the first massive stars. The distinctive chemical abundance patterns of these stars can be used to estimate the masses of the first stars.

    Over the past thirty years astronomers have conducted large-scale investigations to find low-mass, metal-poor stars formed in the early Universe. Follow-up spectroscopic studies, which measured their chemical abundances, have identified stars that recorded the abundance patterns associated with the first stars that had several tens of solar masses and produced large amounts of carbon and other light elements (Note 3). However, no previous research of low-mass metal-poor Milky-Way stars has found the signature of supernova explosions of very-massive stars with more than 100 solar masses, which synthesize large amounts of iron but little carbon (Note 4).

    Discovery of a Low-Mass Star with Unique Chemical Abundance Ratios

    The current team of researchers used the High Dispersion Spectrograph mounted on the Subaru Telescope to conduct a high-resolution spectroscopic follow-up of a large sample of low-mass metal-poor stars (Note 5, Fig. 1) and discovered a star, SDSS001820.5-093939.2 (SDSS J0018-0939), that exhibits a very peculiar set of chemical abundance ratios. Whereas the star contains an amount of iron 300 times lower than the Sun’s, it is significantly deficient in lighter elements such as carbon and magnesium. The extremely low abundances of elements other than iron indicates that this star formed directly from a hydrogen gas cloud that contained elements dispersed by a first-generation massive star.

    Nucleosynthesis models for supernova explosions of massive stars, which successfully reproduce the abundance ratios found in most of the early-generation stars previously known (Fig. 2) do not readily explain the chemical abundance ratios observed in the newly discovered star.

    image 2
    Figure 2: The chemical abundance ratios (with respect to iron) of SDSS J0018-0939 (red circles) compared with model predictions for a supernova explosion of a massive star. The model well-explains the chemical abundance ratios of a comparison star (a similar low-mass star, G39-36; blue triangles), whereas the lighter elements, such as carbon and magnesium, as well as the heavier element cobalt, of SDSS J0018-0939 are not well-reproduced. (Credit: NAOJ)

    Rather, explosion models of very-massive stars can explain both the relatively high abundance ratio of iron as well as the low abundances of lighter elements (Fig. 3). This means that this star most likely preserves the elemental abundance ratios produced by a first-generation very-massive star.

    image 3
    Figure 3: The chemical abundance ratios (with respect to iron) of SDSS J0018-0939 (red circles) compared with model prediction for explosions of very-massive stars. The black line indicates the model of a pair-instability supernova by a star with 300 solar masses, whereas the blue line shows the model of an explosion caused by a core-collapse of a star with 1000 solar masses. The abundance ratios of sodium (Na) and aluminum (Al), which are not well-reproduced by these models, might be produced during the evolution of stars before the explosion, but that is not included in the current model. (Credit: NAOJ)

    Impact of this Study

    The discovery of a star that could have recorded the chemical yields of a first- generation very-massive star will stimulate further modeling of the evolution of very-massive stars and the nucleosynthesis processes that occurred during their explosions. If more detailed modeling of the elemental abundance patterns in this star confirms the existence of very-massive stars, this new discovery will help to focus our understanding of the formation of the first stars and the birth of the elements.

    The strong UV radiation, energetic explosions, and production of heavy elements from very-massive stars influence subsequent star as well as galaxy formation. If stars with masses up to 1000 solar masses existed, their remnants are probably black holes with several hundred solar masses, which may have formed the “seeds” of super-massive black holes, such as found in the Galactic Center.

    Further research to find early generations of low-mass metal-poor stars is necessary to estimate the proportion of very-massive stars among the first stars. If very-massive stars are relatively common, next-generation large telescopes such as the Thirty Meter Telescope (TMT) and the James Webb Space Telescope (JWST) will have the potential to directly detect groups of such first stars in studies of the most distant galaxies (Note 6).

    Thirty Meter Telescope
    TMT

    NASA Webb Telescope
    NASA/Webb

    Reference:

    The research paper on which this release was based, A chemical signature of first-generation very-massive stars by W. Aoki, N. Tominaga, T. C. Beers, S. Honda, Y. S. Lee, is published in Science on August 22, 2014.

    Acknowledgements:

    This study was supported by:

    The JSPS Grants-in-Aid for Scientific Research (23224004)
    Grant PHY 08-22648: Physics Frontiers Center/Joint Institute for Nuclear Astrophysics (JINA), awarded by the U.S. National Science Foundation.

    Notes:

    1.Team members are:
    Wako Aoki (National Astronomical Observatory of Japan)
    Nozomu Tominaga (Konan University & Kavli IPMU [WPI], University of Tokyo)
    Timothy C. Beers (University of Notre Dame)
    Satoshi Honda (University of Hyogo)
    Young Sun Lee (New Mexico State University)
    2. Numerical simulations usually start with considering initial non-uniform distributions (i.e., inhomogeneities) in the dark matter density of small regions formed after the Big Bang. The larger gravitational forces associated with a high-density region gathers normal (i.e., baryonic) matter, such as primordial gas, and the density of the region increases. First stars probably formed in such regions.
    3. A massive star ends its life by collapse of its central core and a supernova explosion, leaving behind a black hole or a neutron star. The explosion ejects a certain amount of heavy elements, from carbon to iron. Previous observations of early-generation low-mass stars have identified stars exhibiting elements produced by such supernovae.

    4. The central temperature of evolved very-massive stars becomes so high that electron-positron pair-creation occurs, resulting in the collapse of the central core, and a nuclear reaction runaway that explodes the star. If the star is more massive than about 300 solar masses, the explosive nuclear reaction is insufficient to prevent the core from collapsing, resulting in the direct formation of a black hole, but some fraction of the material might have still been ejected.
    5. The team conducted chemical abundance measurements based on data obtained with the Subaru Telescope High Dispersion Spectrograph (HDS) for early generations of stars found by the SDSS. SDSS J001820.5-093939.2 (SDSS J0018-0939) is a star showing peculiar abundance ratios among 150 stars studied with the Subaru Telescope. The team used the same instrument to make a more detailed measurement.
    6. Observations of more distant objects allow scientists to study earlier eras of the Universe. Although the next generations of large telescopes may not even be able to distinguish individual first stars, they should be able to observe groups of such stars, if very-massive stars indeed existed.

    Additional Figures:

    image 4
    Figure 4: Artist’s rendition of massive, luminous first-generation stars in the Universe which would form a cluster. The most massive ones, which could be over a 100 times more massive than the Sun, exploded and ejected material that included heavy elements, particularly iron. (Credit: NAOJ)

    image 5
    Figure 5: Artist’s rendition of new generations of stars. The material that included heavy elements from the first-generation, very-massive stars mixed with hydrogen around the star. New generations of stars formed from the gas clouds that included small amount of heavy elements. SDSS J0018-0939, a low-mass star with a long lifetime, formed as one of these second-generation stars, recording the products of a first-generation very-massive star. (Credit: NAOJ)

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    Misuzawa Station Japan
    Mizusawa VERA Observatory

    NAOJ Okayama Astrophysical Observatory Telescope
    Okayama Astrophysical Observatory

    The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

    In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

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  • richardmitnick 6:33 am on March 27, 2014 Permalink | Reply
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    From ALMA: “ALMA Helps to Explain Massive Stars Mysterious Formation” 

    ESO ALMA Array
    ALMA

    Thursday, 27 March 2014
    Contact:

    Tomoya Hirota
    Assistant Professor
    Mizusawa VLBI Observatory
    National Astronomical Observatory of Japan
    Phone: +81-422-34-3645
    Email: tomoya.hirota@nao.ac.jp

    Mareki Honma
    Associate Professor
    Mizusawa VLBI Observatory
    National Astronomical Observatory of Japan
    Phone: +81-422-34-3640
    Email: mareki.honma@nao.ac.jp

    Valeria Foncea
    Education and Public Outreach Officer
    Joint ALMA Observatory
    Santiago, Chile
    Tel: +56 2 467 6258
    Cell: +56 9 75871963
    Email: vfoncea@alma.cl

    Charles E. Blue
    Public Information Officer
    National Radio Astronomy Observatory
    Charlottesville, Virginia, USA
    Tel: +1 434 296 0314
    Cell: +1 434.242.9559
    E-mail: cblue@nrao.edu

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

    Masaaki Hiramatsu
    Education and Public Outreach Officer, NAOJ Chile
    Observatory Tokyo, Japan
    Tel: +81 422 34 3630
    E-mail: hiramatsu.masaaki@nao.ac.jp

    A research team led by Tomoya Hirota (National Astronomical Observatory of Japan: NAOJ) discovered a hot circumstellar disk around a massive protostar by using the Atacama Large Millimeter/Submillimeter Array (ALMA) and the VLBI Exploration of Radio Astrometry (VERA). The formation process of a massive star has been a long-standing problem. The research results favor disk accretion for the formation of massive stars, similar to the formation of low to intermediate mass stars such as the Sun.

    VERA VBLI
    VERA VBLI

    The team observed a radio source called Source I in Orion KL, the nearest massive star-forming region. ALMA detected radio signals from hot water vapor with high angular resolution. The gas temperature reaches around 3000 degrees Celsius. Combining this data with the data taken by VERA, the team confirmed that the hot gas containing water vapor is actually a circumstellar disk around Source I. Thanks to an accurate estimated distance to Source I based on VERA observations, the disk diameter can be estimated at about 80 times larger than the distance between the Sun and Earth.

    image
    Fig. 1 (box): Artist’s impression of Orion KL Source I Credit: NAOJ; Fig 2 (Background): Near-Infrared image of the Orion Nebula taken by the Subaru Telescope. Orion KL is located inside the orange cloud in upper right. The field of view of the ALMA observations is shown with a red circle. Credit: NAOJ; Fig 3: The Atacama Large Millimeter/submillimeter Array (ALMA), ALMA(ESO/NAOJ/NRAO), R. Hills.

    NAOJ Subaru Telescope
    Subaru

    Thanks to recent intensive studies, the formation process of low to intermediate mass stars is now well understood. On the other hand, we know little about how massive stars form. Low and intermediate mass stars are formed by mass accretion from a circumstellar disk. Is this process the same for massive stars? Massive stars could form via stellar collisions as another theory suggests. We cannot answer such a simple question.

    A radio telescope is essential to study the process of star formation because stars form in gas and dust, and a radio telescope observes such interstellar matter. For high resolution, observations by a radio array have a great advantage. Until very recently, the resolution and sensitivity of observational instruments were not high enough for detailed investigations of molecular clouds in which massive stars are forming. To make matters worse, most such clouds are located far from our Solar System. Now, ALMA enables researchers to study actual formation sites of massive stars.

    gbtGreen Bank Radio Telescope, just one example.

    The research team selected the nearest region of massive star-formation, Orion KL, for the ALMA observation. Stars with 8 times more mass than the Sun are forming in Orion KL. The distance to Orion KL is estimated to be about 1400 light-years, and it has been well studied since its discovery in 1967 because of its vicinity.

    antennae
    Fig. 4: Antenna locations of the VERA array. Credit: NAOJ

    The research team carried out observations of Source I in Orion KL with VERA. The team observed the launching point of a bipolar outflow, and found a cluster of vibrationally excited SiO masers tracing an outflow arising from the surface of the disk. The team uncovered a high-speed jet from the region surrounding Source I by observing the SiO masers. The other research group found a compact radio continuum source associated with the center of these vibrationally excited SiO masers. This radio source is interpreted as an edge-on disk. However, the nature of Source I is still controversial. The structure of this region is complex. Many large and small jets are blowing off in various directions. Thus, interpretation of the observations was sometimes different and some researchers deny the existence of the disk and jets.

    Previously, the research team successfully found radio signals emitted by high temperature water vapor by analyzing ALMA’s data. When the data was taken, ALMA was in the science verification phase before full operation so the resolution was not high enough to uncover the nature of the molecular gas associated with the hot water vapor. Hirota, the leader of this study, said, “We proposed additional ALMA observations to understand Source I. We got very good quality data! The resolution is three times higher than the previous data set.”

    The team used the two radio lines emitted by water molecules at the frequencies of 321 GHz and 336 GHz, which are thought to correspond to gas temperatures of 1700 and 2700 degrees Celsius, respectively. Thus, these lines are suitable tracers to study the closest region of Source I.

    gas
    Fig. 5: Distribution of the radio emission from water molecule at 336 GHz observed by ALMA. The color indicates the motion of the water molecule; blue means the gas moving toward us and orange indicates the gas moving away from us. The gray dots shows the distribution of the SiO maser emission. Researchers interprets that the SiO maser traces the root of the jet.

    The team detected the two lines from the hot water molecules and clearly revealed the distribution. The distribution of the emissions from the 1700 degrees Celsius water molecules was similar to that of the jet observed via the SiO maser. The team interpreted this to mean that water molecules in the jet from Source I are emitting the radio maser.

    The radiation from water molecules at 2700 degrees Celsius was found to have a structure similar to that of Source I at the base of the jet. Interestingly, the team found that this hot gas seems to have a disk-like shape. Detailed analysis indicates that the rotational velocity of the disk is 10 km per second.

    The team also found;
    The temperature of the rotating disk reaches 3000 degrees Celsius or higher.
    The central star should have at least 7 times more mass than the Sun.
    The diameter of the disk is estimated as about 80 times larger than the Solar System.
    The radio emissions come from a rotating ring-like structure or limb of the disk viewed edge-on.

    One of the team members, Mareki Honma, said, “Our observations uncovered the nature of Source I, and we can understand the previous observational results about Source I in a consistent manner. These are all thanks to ALMA. Thanks to this state-of-the-art telescope, we can observe the target at higher frequency and higher resolution. In addition, thanks to VERA, we have a good distance estimate to Source I. This results in accurate estimates for the size of the disk and other physical quantities.”

    This study settles the long-standing problem; is Source I a jet or a gas disk. The result clearly shows that Source I is a gas disk.

    The team wants to learn the more detailed structure and dynamics of Source I by using ALMA with higher resolution and sensitivity at higher frequency. Such observations should reveal the mysteries of the evolution of Source I. Hirota said, “It is also important that the physical conditions of a circumstellar disk depend on the mass of the central protostar. The circumstellar disk around a massive star is heated up to 3000 degrees Celsius. Dust that is the material for planets should melt away at such high temperatures. I wonder if planets can form under such condition. I’m interested in the dependence of planet formation on stellar mass and physical conditions.”

    The research findings are presented in the article Hirota et al. A Hot Molecular Circumstellar Disk around the Massive Protostar Orion Source I published in the Astrophysical Journal in February 2014.

    See the full article, with note, here.

    The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA is funded in Europe by the European Organization for Astronomical Research in the Southern Hemisphere (ESO), in North America by the U.S. National Science Foundation (NSF) in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and in East Asia by the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Academia Sinica (AS) in Taiwan.

    ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI) and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

    NRAO Small

    ESO 50

    NAOJ


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  • richardmitnick 2:36 pm on August 1, 2013 Permalink | Reply
    Tags: , , , , Subaru Telescope   

    From NAOJ: “Image of M31 Heralds the Dawn of HSC’s Productivity” 

    NAOJ

    Hyper Suprime-Cam starts the observation and captured first beautiful image of Andromeda Galaxy, M31.

    “A stunning image of M 31 [Andromeda] captured by National Astronomical Observatory of Japan’s Subaru Telescope’s Hyper-Suprime Cam (HSC) displays the fruits of international collaboration and technological sophistication aligned with cutting-edge science. In addition to providing information about a nearby galaxy that resembles our own, this image demonstrates HSC’s capability to fulfill Subaru Telescope’s intention of producing a large-scale survey of the Universe. The combination of a large mirror, a wide field of view, and sharp imaging represents a giant step into a new era of observational astronomy and will contribute to answering questions about the nature of dark energy and matter. It marks another successful stage in HSC’s commissioning process, which involves checking all of HSC’s capabilities before it is ready for open use.

    sub

    inside

    Subaru

    hsc
    Hyper-Suprime Cam (HSC)

    m31
    Andromeda

    The gigantic camera, which contains multiple lenses around 2.6-feet in diameter, is preparing for a much larger task: a cosmic census. Astronomers plan to use the massive telescope to explore the dark passages of the universe.

    ‘This first image from HSC is truly exciting. We can now start the long-awaited, largest-ever galaxy survey for understanding the evolutionary history and fate of the expanding universe,’ said Masahiro Takada, a chair for HSC’s science group. Astronomers plan to use the Subaru Telescope to observe hundreds of millions of galaxies, specifically analyzing the various arrangements of each and further exploring the effects of gravitational lensing.’Such data will allow scientists to map the distribution of dark matter, constrain the nature of dark energy, and search for baby galaxies that were just born in the early universe,’ Takada noted. (CNET, Christopher MacManus July 31, 2013)


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