具有显著轨道运动的恒星双星透镜中焦散穿越微透镜事件的发生率
Rate of caustic crossing microlensing events in stellar binary lenses with significant orbital motion
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中文总结 AI 辅助
研究具有显著轨道运动的恒星双星透镜中焦散穿越微透镜事件发生率，通过合成样本计算有、无轨道运动时焦散穿越截面平均变化及总体发生率，发现总体平均截面仅微小增加，发生率可用于检验对相关属性的理解。
中文摘要 AI 辅助
二元透镜微透镜事件中，源穿过焦散会产生尖锐、独特的放大峰值，因此易于识别。本文探讨了二元轨道运动对二元透镜焦散穿越截面的重要性。若二元系统的轨道时标小于爱因斯坦环穿越时标，焦散在源平面扫过更大区域，通常会增大截面。我们发现，圆形轨道的正面双星焦散穿越截面大幅增加（高达4倍）。然而，高倾角轨道相对于具有相同半长轴的静态正面双星会使截面净减小。利用从现实的银河系种群合成模型中抽取的约2800个合成二元微透镜事件样本，我们计算了有和无轨道运动的单个系统焦散穿越截面的平均变化。虽然轨道运动可显著改变特定几何形状的截面，但总体平均时，仅使平均截面产生约0.1%的微小、可忽略不计的增加。我们还计算了模拟样本中焦散穿越二元事件的总体发生率，发现通过足够密集的光度采样，撞击参数\(u_0 < 1\)的微透镜事件中有\(6.3 \pm 0.2\%\)应会出现焦散穿越。该发生率取决于双星间距、质量比以及恒星和致密天体的多重性分布，因此可用于检验我们对这些基本属性的理解。
英文摘要
Binary lens microlensing events in which the source crosses a caustic produce sharp, distinctive magnification peaks and can therefore be readily identified. In this paper, we explore the importance of binary orbital motion for the binary lens caustic crossing cross section. If the orbital timescale of the binary system is smaller than the Einstein ring crossing timescale, the caustics sweep out a larger area in the source plane, generally enhancing the cross section. We find that face-on binaries in circular orbits exhibit a substantial increase (up to 4$\times$) in the cross section for caustic crossings. However, highly inclined orbits produce a net decrease relative to a static face-on binary with the same semi-major axis. Using a sample of ~$2800$ synthetic binary microlensing events drawn from a realistic Milky Way population-synthesis model, we calculate the average change in the caustic crossing cross section for individual systems with and without orbital motion. Although orbital motion can significantly alter the cross section for specific geometries, we find that, when averaged over the full population, it produces only a small, negligible increase of ~$0.1\%$ in the average cross section. We also compute the overall rate of caustic crossing binary events in the simulated sample and find that, with sufficiently dense photometric sampling, $6.3 \pm 0.2\%$ of microlensing events with impact parameter $u_0 < 1$ should exhibit caustic crossings. This rate depends on the distributions of binary separation, mass ratio, and multiplicity of stars and compact objects, and can therefore be used to test our understanding of these underlying properties.
