Study of the Galactic Structure using Astrometric Microlensing
Grant-in-Aid for Scientific Research (C)
|Allocation Type||Single-year Grants|
|Research Institution||Nagano National College of Technology|
OHNISHI Kouji Nagano National College of Technology, General Education, Associate Professor, 一般科, 助教授 (20290744)
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
Completed(Fiscal Year 2006)
|Budget Amount *help
¥3,000,000 (Direct Cost : ¥3,000,000)
Fiscal Year 2006 : ¥700,000 (Direct Cost : ¥700,000)
Fiscal Year 2005 : ¥700,000 (Direct Cost : ¥700,000)
Fiscal Year 2004 : ¥700,000 (Direct Cost : ¥700,000)
Fiscal Year 2003 : ¥900,000 (Direct Cost : ¥900,000)
|Keywords||Gravitational Lens / Gravitational Microlensing / Astrometry / Astrometric Microlensing / Galaxy / Gravitational Macro-lens / Galactic Center / Tago Event / Sgr A* / アストロメトリック・マイクロレンズ / 重力レンズ効果 / マクロ重力レンズ / 近傍銀河|
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
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.
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 (16results)