THE EXOPLANET MASS-RATIO FUNCTION FROM THE MOA-II SURVEY: DISCOVERY OF A BREAK AND LIKELY PEAK AT A NEPTUNE MASS-猫眼课题宝

DOI：

10.3847/1538-4357/833/2/145

发表时间：

2016-12

期刊：

The Astrophysical Journal

影响因子：

通讯作者：

中科院分区：

其他

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作者：

D. Suzuki;D. Bennett;T. Sumi;I. Bond;L. Rogers;F. Abe;Y. Asakura;A. Bhattacharya;M. Donachie;M. Freeman;A. Fukui;Y. Hirao;Y. Itow;N. Koshimoto;M. Li;C. Ling;K. Masuda;Y. Matsubara;Y. Muraki;M. Nagakane;K. Onishi;H. Oyokawa;N. Rattenbury;T. Saito;A. Sharan;H. Shibai;D. Sullivan;P. Tristram;A. Yonehara

我们报告了 2007 年至 2012 年 MOA-II 微透镜巡天警报系统事件中发现的行星信号的统计分析结果。我们将巡天灵敏度确定为行星-恒星质量比 q 和预计的行星-恒星间隔 s（以爱因斯坦半径单位表示）的函数。我们发现质量比函数不是单一的幂律，而是在 q ∼ 10−4 处有斜率变化，对应于 ∼20 M⊕ 的主恒星中值质量 ∼0.6 。我们在 1474 个警报事件中的 23 个中发现了重要的行星信号，这些信号仅通过 MOA-II 调查数据就得到了很好的表征。来自其他组的数据仅用于表征仅在 MOA 数据中识别的行星信号。我们的样本中发现的质量比和行星间距的分布非常适合 q > qbr 和 q < qbr 形式的破碎幂律模型，其中 qbr 是破碎的质量比。我们还将这一分析与古尔德等人之前的分析结合起来。 Cassan 等人将样本总数增加到 30 个行星。该组合分析得出 , n = −0.93 ± 0.13, , 且 qbr ≡ 1.7 × 10−4。不破坏幂律模型的 p 值为 0.0022，这对应于有利于破坏幂律模型的贝叶斯因子 27。这些结果意味着寒冷的海王星可能是雪线以外最常见的行星类型。

We report the results of the statistical analysis of planetary signals discovered in MOA-II microlensing survey alert system events from 2007 to 2012. We determine the survey sensitivity as a function of planet–star mass ratio, q, and projected planet–star separation, s, in Einstein radius units. We find that the mass-ratio function is not a single power law, but has a change in slope at q ∼ 10−4, corresponding to ∼20 M⊕ for the median host-star mass of ∼0.6 . We find significant planetary signals in 23 of the 1474 alert events that are well-characterized by the MOA-II survey data alone. Data from other groups are used only to characterize planetary signals that have been identified in the MOA data alone. The distribution of mass ratios and separations of the planets found in our sample are well fit by a broken power-law model of the form for q > qbr and for q < qbr, where qbr is the mass ratio of the break. We also combine this analysis with the previous analyses of Gould et al. and Cassan et al., bringing the total sample to 30 planets. This combined analysis yields , n = −0.93 ± 0.13, , and for qbr ≡ 1.7 × 10−4. The unbroken power-law model is disfavored with a p-value of 0.0022, which corresponds to a Bayes factor of 27 favoring the broken power-law model. These results imply that cold Neptunes are likely to be the most common type of planets beyond the snow line.

THE EXOPLANET MASS-RATIO FUNCTION FROM THE MOA-II SURVEY: DISCOVERY OF A BREAK AND LIKELY PEAK AT A NEPTUNE MASS

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