Kojima-1 Lb是一个围绕Brilliant Microlensing主星的温和冷海王星
Kojima-1Lb Is a Mildly Cold Neptune around the Brightest Microlensing Host Star
摘要：
我们报告了对附近行星微透镜事件TCP J 05074264 +2447555（Kojima-1）的额外多波段光度学和光谱学以及新的自适应光学（AO）成像的分析，该事件于2017年在银河系反中心发现（Nucita等人）。我们确认了峰值周围光变曲线异常的行星性质，同时在这次事件中没有发现其他行星特征。我们还证实了存在明显的融合通量和文献中报道的显着视差信号的情况下。AO图像显示没有污染源，使得混合通量最有可能来自透镜星。测量的多波段透镜通量，结合微透镜模型的约束，使我们能够缩小以前未解决的质量和距离的透镜系统。我们发现主透镜是位于K/M边界的矮星（0.581 \pm 0.033 M_sun），位于505 \pm 47 pc，伴星（Kojima-1 Lb）是一颗海王星质量的行星（20.0 \pm 2.0 M_地球），半长轴为1.08 ^{+0.62}_{-0.18} au。这个轨道比典型的微透镜行星小几倍，与年轻时的雪线位置相当。我们计算出小岛-1Lb的先验检测概率只有\sim 35%，这可能意味着海王星是常见的雪线周围，最近提出的过境和径向速度技术。主恒星是微透镜行星系中最亮的（Ks = 13.7），即使使用现有的设施，也提供了一个很好的机会来光谱表征这个系统。
英文摘要：
We report the analysis of additional multiband photometry and spectroscopy and new adaptive optics (AO) imaging of the nearby planetary microlensing event TCP J05074264+2447555 (Kojima-1), which was discovered toward the Galactic anticenter in 2017 (Nucita et al.). We confirm the planetary nature of the light-curve anomaly around the peak while finding no additional planetary feature in this event. We also confirm the presence of apparent blending flux and the absence of significant parallax signal reported in the literature. The AO image reveals no contaminating sources, making it most likely that the blending flux comes from the lens star. The measured multiband lens flux, combined with a constraint from the microlensing model, allows us to narrow down the previously unresolved mass and distance of the lens system. We find that the primary lens is a dwarf on the K/M boundary (0.581 \pm 0.033 M_sun) located at 505 \pm 47 pc and the companion (Kojima-1Lb) is a Neptune-mass planet (20.0 \pm 2.0 M_earth) with a semi-major axis of 1.08 ^{+0.62}_{-0.18} au. This orbit is a few times smaller than those of typical microlensing planets and is comparable to the snow-line location at young ages. We calculate that the a priori detection probability of Kojima-1Lb is only \sim 35%, which may imply that Neptunes are common around the snow line, as recently suggested by the transit and radial velocity techniques. The host star is the brightest among the microlensing planetary systems (Ks = 13.7), offering a great opportunity to spectroscopically characterize this system, even with current facilities.
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