标题： 2021年高时间分辨率微透镜巡天中发现的双星中的褐矮星伴星 显示英文标题

标题： Brown dwarf companions in binaries detected from the 2021 season high-cadence microlensing surveys

摘要： 作为旨在构建包含棕矮星（BD）伴星的同质双透镜（2L1S）事件样本的项目的一部分，我们研究了由韩国微透镜望远镜网络（KMTNet）调查收集的2021年微透镜数据。 为此，我们首先通过系统分析异常透镜事件来识别2L1S事件。 然后，我们通过应用透镜组分之间的质量比小于$q_{\rm th}\sim 0.1$的标准来选择候选的BD伴星事件。 通过这一过程，我们发现了四个双透镜事件，包括KMT-2021-BLG-0588、KMT-2021-BLG-1110、KMT-2021-BLG-1643和KMT-2021-BLG-1770，其估计的质量比分别为$q\sim 0.10$、0.07、0.08和0.15。 尽管事件KMT-2021-BLG-1770的质量比略大于$q_{\rm th}$，但由于该事件测量的短时间尺度$t_{\rm E}\sim 7.6$~天，预期的透镜质量较小，因此仍被选为候选事件。 从贝叶斯分析中，我们估计主星和伴星的质量分别为 KMT-2021-BLG-0588L 的$(M_1/M_\odot, M_2/M_\odot)= (0.54^{+0.31}_{-0.24}, 0.053^{+0.031}_{-0.023})$，KMT-2021-BLG-1110L 的$(0.74^{+0.27}_{-0.35}, 0.055^{+0.020}_{-0.026})$，KMT-2021-BLG-1643L 的$(0.73^{+0.24}_{-0.17}, 0.061^{+0.020}_{-0.014})$，以及 KMT-2021-BLG-1770L 的$(0.13^{+0.18}_{-0.07}, 0.020^{+0.028}_{-0.011})$。 估计透镜伴星处于棕矮星质量范围的概率分别为 82%、85%、91% 和 59% 对于各个事件。 为了通过未来高分辨率自适应光学（AO）后续观测直接成像透镜来确认本次研究及之前研究中发现的透镜伴星的棕矮星性质，我们提供了 2030 年预期的透镜-源分离距离，这是第一代 30~m 级望远镜开始 AO 观测的近似年份。 显示英文摘要

摘要： As a part of the project aiming to build a homogeneous sample of binary-lens (2L1S) events containing brown-dwarf (BD) companions, we investigate the 2021 season microlensing data collected by the Korea Microlensing Telescope Network (KMTNet) survey. For this purpose, we first identify 2L1S events by conducting systematic analyses of anomalous lensing events. We then select candidate BD-companion events by applying the criterion that the mass ratio between the lens components is less than $q_{\rm th}\sim 0.1$. From this procedure, we find four binary-lens events including KMT-2021-BLG-0588, KMT-2021-BLG-1110, KMT-2021-BLG-1643, and KMT-2021-BLG-1770, for which the estimated mass ratios are $q\sim 0.10$, 0.07, 0.08, and 0.15, respectively. The event KMT-2021-BLG-1770 is selected as a candidate despite the fact that the mass ratio is slightly greater than $q_{\rm th}$ because the lens mass expected from the measured short time scale of the event, $t_{\rm E}\sim 7.6$~days, is small. From the Bayesian analyses, we estimate that the primary and companion masses are $(M_1/M_\odot, M_2/M_\odot)= (0.54^{+0.31}_{-0.24}, 0.053^{+0.031}_{-0.023})$ for KMT-2021-BLG-0588L, $(0.74^{+0.27}_{-0.35}, 0.055^{+0.020}_{-0.026})$ for KMT-2021-BLG-1110L, $(0.73^{+0.24}_{-0.17}, 0.061^{+0.020}_{-0.014})$ for KMT-2021-BLG-1643L, and $(0.13^{+0.18}_{-0.07}, 0.020^{+0.028}_{-0.011})$ for KMT-2021-BLG-1770L. It is estimated that the probabilities of the lens companions being in the BD mass range are 82\%, 85\%, 91\%, and 59\% for the individual events. For confirming the BD nature of the lens companions found in this and previous works by directly imaging the lenses from future high-resolution adaptive-optics (AO) followup observations, we provide the lens-source separations expected in 2030, which is an approximate year of the first AO light on 30~m class telescopes.