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2006 Fiscal Year Final Research Report Summary

Study of the Galactic Structure using Astrometric Microlensing

Research Project

Project/Area Number 15540240
Research Category

Grant-in-Aid for Scientific Research (C)

Allocation TypeSingle-year Grants
Section一般
Research Field Astronomy
Research InstitutionNagano National College of Technology

Principal Investigator

OHNISHI Kouji  Nagano National College of Technology, General Education, Associate Professor, 一般科, 助教授 (20290744)

Co-Investigator(Kenkyū-buntansha) FUKUSHIMA Toshio  National Astronomical Observatory of Japan, Public Relations Center, Professor, 天文情報センター, 教授 (70231735)
Project Period (FY) 2003 – 2006
KeywordsGravitational Lens / Gravitational Microlensing / Astrometry / Astrometric Microlensing / Galaxy / Gravitational Macro-lens / Galactic Center / Tago Event
Research Abstract

Astrometric Microlensing(the positional shift due to gravitational lens effect by stars, MACHOs and the Galaxy) is useful to study the structure of our galaxy.
(1)Astrometric study of MACHO halo distribution in our Galaxy
We estimated the optical depth and event rate of micro-arcsecond level astrometric microlensing for the stars outside our galaxy caused by MACHOs. For the stars in the LMC and the SMC, the optical depth of 1 micro-arcsecond detection threshold is on the order of 0.1 and the event rate of the induced proper motion of 1 micro-arcsecond/year is on the order of 0.001/yr. They depend on the distribution of lenses and sources. This poses a constraint on the expected probability of photometric self-lensing in LMC and SMC.
(2)Macrolens toward the Galactic Center
The motion of Sgr A^* has been measured by referring to QSOs in the direction of Galactic Center. The QSOs referred in the observations are close to Sgr A^* on the celestial sphere. This means that we observe these QSOs t … More hrough the core, the bulge, and the disk of the Galaxy where stars are very densely distributed. Therefore, the observed position of QSOs may vary due to the gravitational deflection by foreground objects, e.g. stars and our Galaxy itself. We consider the macro lens effect, the collective gravitational deflection by the core and the bulge of the Galaxy. Its magnitude is the order of 1 micro-arcsecond/yr. However, this effect is important because it has a secular component. The measurement of these effects will provide us valuable information on the density and mass function of the Galactic Center.
(3)Discovery of the cool planet through gravitational lensing
Gravitational Microlensing events can reveal extraSolar planet orbiting the foreground lending stars. We found the cool planet of 5.5 Earth masses by MOA project for investigating the structure in our galaxy using photometric microlensing observation.
(4)TAGO Event.
We report the observation of the first gravitational microlensing event on a very close(1kpc) bright star in a sparse stellar field. A. Tago discovered this event on 31 October 2006 towards the Cassiopeia constellation. The light curve analyses indicate that this event was caused by the gravitational microlensing rather than a genuine variable star. The provability of such a high magnification in nearby stars is much small. This may be just a good luck, or true event rate is higher than expected due to (unknown) low mass star distribution function on disk structure in our galaxy. Less

  • Research Products

    (11 results)

All 2007 2006 2005 2004 2003

All Journal Article (7 results) Book (4 results)

  • [Journal Article] Macrolens toward the Galactic Center2007

    • Author(s)
      Kouji Ohnishi
    • Journal Title

      Mapping the Galaxy and Nearby Galaxies (Edited by Keiichi Wada and Francoise Combes)(Springer)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Journal Article] Discovery of a cool planet of 5.5 Earth masses through gravitational microlensing2006

    • Author(s)
      J.-P.Beaulieu
    • Journal Title

      Nature 439

      Pages: 437-440

    • Description
      「研究成果報告書概要(和文)」より
  • [Journal Article] Astrometric microlensing and degradation of reference frames2005

    • Author(s)
      Mizuhiko Hosokawa
    • Journal Title

      Highlights of Astronomy, Vol. 13, as presented at the XXVth General Assembly of the IAU-2003 (Edited by O.Engvold.)(San Francisco, CA : Astronomical Society of the Pacific)

      Pages: 602

    • Description
      「研究成果報告書概要(欧文)」より
  • [Journal Article] Macro Lens toward the Galactic Center2004

    • Author(s)
      Kouji Ohnishi
    • Journal Title

      Progress of Theoretical Physics Supplement 155

      Pages: 395-396

    • Description
      「研究成果報告書概要(和文)」より
  • [Journal Article] Macro Lens toward the Galactic Center2004

    • Author(s)
      Kouji Ohnishi
    • Journal Title

      Progress of Theoretical Physics Supplement155

      Pages: 395-396

    • Description
      「研究成果報告書概要(欧文)」より
  • [Journal Article] Astrometric study of MACHO halo distribution in our Galaxy.2004

    • Author(s)
      Kouji Ohnishi
    • Journal Title

      Dark Matter in Galaxies ; International Astronomical Union Symposium (Eds : S.D.Ryder, D.J.Pisano, M.A.Walker, and K.C.Freeman.)(San Francisco : Astronomical Society of the Pacific.) no.220

      Pages: 135-136

    • Description
      「研究成果報告書概要(欧文)」より
  • [Journal Article] Secular Component of Apparent Proper Motion of QSOs Induced by Gravitational Lens of the Galaxy2003

    • Author(s)
      Kouji Ohnishi
    • Journal Title

      The Proceedings of the IAU 8th Asian-Pacific Regional Meeting, Volume I, ASP Conference Proceedings (Edited by Satoru Ikeuchi, John Hearnshaw and Tomoyuki Hanawa.)(Astronomical Society of the Pacific) Vol.289

      Pages: 461-464

    • Description
      「研究成果報告書概要(欧文)」より
  • [Book] Mapping the Galaxy and Nearby Galaxies2007

    • Author(s)
      Keiichi Wada
    • Total Pages
      2
    • Publisher
      Springer (in Press)
    • Description
      「研究成果報告書概要(和文)」より
  • [Book] Highlights of Astronomy, Vol. 132005

    • Author(s)
      O.Engvold
    • Total Pages
      1
    • Publisher
      Astronomical Society of the Pacific
    • Description
      「研究成果報告書概要(和文)」より
  • [Book] Dark Matter in Galaxies, International Astronomical Union Symposium No.2202004

    • Author(s)
      S.D.Ryder
    • Total Pages
      2
    • Publisher
      Astronomical Society of the Pacific
    • Description
      「研究成果報告書概要(和文)」より
  • [Book] The Proceedings of the IAU 8th Asian-Pacific Regional Meeting, Volume I, ASP Conference Proceedings, Vol. 289 (Edited by Satoru Ikeuchi, John Hearnshaw and Tomoyuki Hanawa.)2003

    • Author(s)
      Satoru Ikeuchi
    • Total Pages
      4
    • Publisher
      Astronomical Society of the Pacific
    • Description
      「研究成果報告書概要(和文)」より

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Published: 2008-05-27  

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