MOA-2020-BLG-108Lb：一颗位于质量比荒漠下限附近低质量透镜雪线之外的巨行星
MOA-2020-BLG-108Lb: A Giant Planet Beyond the Snow Line of a Low-Mass Lens Near the Lower Boundary of the Mass-Ratio Desert
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中文总结 AI 辅助
研究微引力透镜事件MOA-2020-BLG-108，通过分析光变曲线找到双透镜单源解，检测有限源效应并进行贝叶斯分析，确定透镜系统参数，发现其巨行星在雪线外且位于质量比荒漠下限附近，为理解行星形成机制提供新数据点。
中文摘要 AI 辅助
我们对微引力透镜事件MOA-2020-BLG-108进行了分析，该事件于2020年6月由MOA合作团队在朝向银心方向发现。观测到的光变曲线显示出与标准单透镜单源模型有显著偏差。我们找到了两个简并的双透镜单源解，对应宽和近两种构型，伴星与主星质量比$q\sim0.02$，投影主伴星间距分别为$s = 1.33\pm0.01$和$s = 0.76\pm0.01$。与单透镜模型相比，这些解使拟合优度提高了$\Delta\chi^2>4430$。我们在光变曲线中检测到了有限源效应，得到角爱因斯坦半径$\theta_{\rm E} = 0.7\pm0.1\:\mathrm {mas}$，这为透镜提供了质量-距离关系。我们进行了贝叶斯分析来估计透镜系统的物理参数。结果表明，透镜系统由一颗质量约为$M_{\rm L,H} \sim 0.6\:M_\odot$、距离约为$D_{\rm L}\sim5$ kpc的主恒星和一颗质量约为$M_{\rm L,C}\sim10\:M_{\rm {Jup}}$、在雪线之外轨道运行的巨行星组成。传统行星形成理论表明，巨行星不太可能在低质量恒星周围形成。此外，一些统计研究表明在$0.02 \lesssim q \lesssim 0.05$范围内存在伴星与主星质量比荒漠，而本工作中发现的透镜系统中的伴星位于该荒漠的下限附近。靠近行星-褐矮星边界的天体可能通过多种途径形成，这一发现为理解它们的形成机制提供了一个额外的数据点。
英文摘要
We present an analysis of the microlensing event MOA-2020-BLG-108, which was discovered in June 2020 by the MOA collaboration toward the Galactic bulge. The observed light curve shows significant deviations from the standard single-lens single-source model. We find two degenerate binary-lens single-source solutions, corresponding to the wide and close configurations, with a companion-to-host mass ratio of $q\sim0.02$ and projected host--companion separations of $s=1.33\pm0.01$ and $s=0.76\pm0.01$, respectively. These solutions improve the fit by $Δχ^2>4430$ compared to the single-lens model. We detected the finite-source effect in the light curve and obtained the angular Einstein radius of $θ_{\rm E} = 0.7\pm0.1\:\mathrm {mas}$, which provides a mass--distance relation for the lens. We conducted a Bayesian analysis to estimate the physical parameters of the lens system. The results indicate that the lens system consists of a host star with a mass of $M_{\rm L,H} \sim 0.6\:M_\odot$ at a distance of $D_{\rm L}\sim5$ kpc and a giant planet with a mass of $M_{\rm L,C}\sim10\:M_{\rm {Jup}}$ orbiting beyond the snow line. Conventional planet formation theories suggest that giant planets are unlikely to form around low-mass stars. Furthermore, several statistical studies have suggested the existence of a companion-to-host mass-ratio desert in the range $0.02 \lesssim q \lesssim 0.05$, and the companion in the lens system discovered in this work lies near the lower boundary of this desert. Objects near the planet-brown dwarf boundary may form through multiple pathways, and this discovery provides an additional data point for understanding their formation mechanisms.
