DETECTION OF WIDE PLANETARY SYSTEM WITH MICROLENSING

  • Ryu, Yoon-Hyun (Department of Astronomy and Atmospheric Sciences, Kyungpook National University) ;
  • Park, Myeong-Gu (Department of Astronomy and Atmospheric Sciences, Kyungpook National University) ;
  • Chang, Heon-Young (Department of Astronomy and Atmospheric Sciences, Kyungpook National University) ;
  • Lee, Ki-Won (Institute of Liberal Education, Catholic University of Daegu)
  • Published : 2012.10.17

Abstract

Recent results from microlensing surveys show that a free-floating planet or a wide-separation planet is more numerous than a main-sequence star in the Galaxy. Moreover, the detection efficiency of the planets will be improved in next-generation experiments with a high survey monitoring frequency. However, microlensing events produced by both planets appear similar light curves with a short duration timescale, thus it is difficult to distinguish them. In this paper, we investigated the detectable separation range of a wide-separation planet as the planet bound to its host star. We construct the fractional deviation maps using the magnifications of the planetary lensing and the single-lensing by planet itself for various parameters such as a mass ratio, separation, and source radius. As a result, we found that the pattern of the fractional deviation is related to the ratio of source radius to caustic size, and the ratio satisfying the detection criterion (i.e., ${\geq}5%$ in the fractional deviation) varies with a separation. Hence, we derived a fitting formula as the function of a mass ratio and a source radius to reflect the variation in the calculations of the detectable separation range of a wide-separation planet as the planet bound to its host star. In addition, we estimated the condition that a wide-separation planet can be detected as a single-lensing event under the finite source effect. We found that such a case is possible provided that the source radius is smaller than ~2.5 times of Einstein ring radius of a planet, regardless of a separation or a mass ratio.

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