宽距离行星的微透镜：可探测性和有界性
Microlensing by a wide-separation planet: detectability and boundness
摘要：
通过对不同微透镜参数，特别是对源星大小的微透镜参数的行星焦散引起的微扰，探讨了宽距行星的探测条件。通过构造微透镜参数空间中不同位置的分数偏差图，我们发现分数偏差的模式依赖于源半径与焦散尺寸的比值，满足观测阈值的比值随星-行星距离的变化而变化。我们还得到了上限的源大小，允许检测的主机星的签名作为一个函数的分离给定的观测阈值。它表明，这种关系进一步导致一个简单的分析条件的恒星-行星分离检测宽分离行星作为质量比和源半径的函数的有界性。例如，当假设探测阈值为5%时，对于一颗半径为~1 R_sun的源星，当其距离在~10 AU和~30 AU范围内时，可分别识别出一颗地球质量的行星和一颗100倍质量的行星。我们还比较了行星焦散线和中心焦散线的分离范围。研究发现，当分析行星焦散引起的微透镜光变曲线时，人们可能比分析中心焦散引起的微透镜光变曲线时更能支持宽分离行星的有界性。最后，我们简要讨论了我们的研究结果对下一代微透镜实验的影响。
英文摘要：
We explore the detection condition of a wide-separation planet through the perturbation induced by the planetary caustic for various microlensing parameters, especially for the size of the source stars. By constructing the fractional deviation maps at various positions in the space of microlensing parameters, we find that the pattern of the fractional deviation depends on the ratio of the source radius to the caustic size, and the ratio satisfying the observational threshold varies with the star-planet separation. We have also obtained the upper limits of the source size that allows the detection of the signature of the host star as a function of the separation for given observational threshold. It is shown that this relation further leads one to a simple analytic condition for the star-planet separation to detect the boundness of wide-separation planets as a function of the mass ratio and the source radius. For example, when 5% of the detection threshold is assumed, for a source star with the radius of ~1 R_sun, an Earth-mass planet and a Jupiter-mass planet can be recognized of its boundness when it is within the separation range of ~10 AU and ~30 AU, respectively. We also compare the separation ranges of detection by the planetary caustic with those by the central caustic. It is found that when the microlensing light curve caused by the planetary caustic happens to be analyzed, one may afford to support the boundness of the wide-separation planet farther than when that caused by the central caustic is analyzed. Finally, we conclude by briefly discussing the implication of our findings on the next-generation microlensing experiments.
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