Study of the Galactic Structure using Astrometric Microlensing

天体测量微透镜（由于恒星、MACHO和银河系的引力透镜效应而引起的位置偏移）对研究银河系的结构很有用。（1）银河系中MACHO晕分布的天体测量研究我们估算了MACHO引起的银河系外恒星微弧秒级天体测量微透镜的光学深度和事件率。对于LMC和SMC中的恒星，1微弧秒探测阈值的光学深度约为0.1，1微弧秒/年的诱导自行事件率约为0.001/年。它们取决于透镜和光源的分布。这对LMC和SMC中的光度自透镜的预期概率构成约束。（2）向银心方向的巨透镜体Sgr A^* 的运动是参照类星体向银心方向的运动来测量的。观测中提到的类星体在天球上接近Sgr A^*。这意味着我们观察到这些类星体 ...更多信息 穿过星系的核心、凸起和星盘，那里的恒星分布非常密集。因此，观测到的类星体的位置可能会因前景物体（如恒星和银河系本身）的引力偏转而发生变化。我们考虑了宏观透镜效应、星系核和星系核球的集体引力偏转。它的大小为1微弧秒/年。然而，这种影响是重要的，因为它有一个长期的成分。对这些效应的测量将为我们提供关于银河系中心密度和质量函数的有价值的信息。（3）通过引力透镜发现冷行星引力微透镜事件可以揭示太阳系外行星围绕前景恒星运行。MOA计划利用光度微透镜观测研究银河系的结构，我们发现了一颗质量为5.5个地球的冷行星。（4）TAGO事件：首次观测到稀疏星场中一颗非常近（1 kpc）的亮星星发生引力微透镜事件。A. Tago于2006年10月31日在仙后座发现了这一事件。光变曲线分析表明，这一事件是由引力微透镜而不是一个真正的可变星星。在附近的恒星中能证明如此高的放大率是很小的。这可能只是一个好运气，或真正的事件率高于预期，由于（未知）低质量星星分布函数的磁盘结构在我们的星系。少

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 GalaxyWe 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 CenterThe 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 lensingGravitational 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