EXTENDED-SOURCE EFFECT AND CHROMATICITY IN TWO-POINT-MASS MICROLENSING
EXTENDED-SOURCE EFFECT AND CHROMATICITY IN TWO-POINT-MASS MICROLENSING
复制标题
两点质量微透镜中的扩展源效应和色度
DOI：
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发表时间：
2007
期刊：
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通讯作者：
D. Heyrovský
中科院分区：
文献类型：
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作者：
O. Pejcha;D. Heyrovský
我们探讨了两点质量引力微透镜对源恒星的扩展性质的敏感性，以及对其边缘暗化的相关敏感性。我们证明了敏感区通常被限制在沿焦散线的源径宽的带内，在尖端附近强烈地扩展，最显著的是沿着它们的外轴。在多分量焦散的情况下，面对的尖端可能形成一个区域，该区域具有跨越它们之间的间隙的不可忽略的扩展源效应。我们证明，对于较小的源，从以源半径为单位测量的尖点延伸的敏感区域的大小增加，按半径的反立方根进行缩放。我们研究了不同灵敏度等高线的范围，结果表明，对于微透镜银河膨胀巨星，当在典型的透镜-分量分离范围内平均时，遇到至少1%的扩展源效应的概率比焦散交叉的概率高40%-60%，实际值取决于分量的质量比。我们推导出焦散外光源的扩展源效应和色度的解析表达式。这些公式更普遍地适用于任何具有足够小的源的引力透镜。使用精确计算的放大，我们测试了通常使用的线性折叠焦散近似，并表明，即使在接近理想的焦散交叉事件中，它也可能导致几个百分点的误差。最后，我们讨论了观测到的双星和行星微透镜事件的几个有趣的例子，并指出我们的结果对于从微透镜光曲线测量恒星边缘暗化的重要性。
We explore the sensitivity of two-point-mass gravitational microlensing to the extended nature of the source star, as well as the related sensitivity to its limb darkening. We demonstrate that the sensitive region, usually considered to be limited to a source-diameter-wide band along the caustic, is strongly expanded near cusps, most prominently along their outer axis. In the case of multicomponent caustics, facing cusps may form a region with a non-negligible extended-source effect spanning the gap between them. We demonstrate that for smaller sources the size of the sensitive region extending from a cusp measured in units of source radii increases, scaling as the inverse cube root of the radius. We study the extent of different sensitivity contours and show that for a microlensed Galactic bulge giant the probability of encountering at least a 1% extended-source effect is higher than the probability of caustic crossing by 40–60% when averaged over a typical range of lens-component separations, with the actual value depending on the mass ratio of the components. We derive analytical expressions for the extended-source effect and chromaticity for a source positioned off the caustic. These formulae are more generally applicable to any gravitational lens with a sufficiently small source. Using exactly computed amplifications we test the often used linear-fold caustic approximation and show that it may lead to errors on the level of a few percent even in near-ideal caustic-crossing events. Finally, we discuss several interesting cases of observed binary and planetary microlensing events and point out the importance of our results for the measurement of stellar limb darkening from microlensing light curves.