论文标题
K2探测的轨道行星的外部球星的发生率
The occurrence rate of exoplanets orbiting ultracool dwarfs as probed by K2
论文作者
论文摘要
随着Trappist-1周围的行星系统的发现，对超级矮人作为潜在的行星宿主的兴趣激增。 Ultracool矮人周围的行星系统代表了我们用JWST表征温带岩石星空大气的最佳机会。但是，Trappist-1仍然是同类系统中唯一已知的系统，并且在Ultracool矮人周围的行星的发生率仍然受到限制。我们试图对NASA K2任务观察到的超速矮人进行完整的过境搜索，以限制这些恒星周围行星的发生率。我们通过拟合光谱能量分布并使用Gaia的视差来过滤和表征K2观察到的Ultracool矮人样品。我们构建了一个自动管道来执行光度法，降低光弯曲并搜索过渡。使用管道的广泛注射回收测试，我们计算搜索的检测灵敏度，从而计算样本的完整性。我们推断出层次贝叶斯模型（HBM）内的行星发生率，以治疗不确定的行星参数。通过逐步函数参数的出现率，我们展示了一种在HBM（行星参数）的第二级直接边缘化的方便方法。我们的方法通常适用，并且可以大大加快较大的检测行星目录。我们在702个Ultracool矮人样本中检测到一个行星：先前验证的迷你新闻。因此，我们在轨道周期内推断出η= 0.20+0.20.16-0.11的微型纽约（2-4re）的发生率在1-20天内。对于1-20天内的超级毕业石（1-2RE）和冰/气巨人（4-6RE），我们分别将95％的可信间隔放置在η<1.14和η<0.29。如果Trappist-1样系统无处不在，我们将有96％的机会至少找到一个。
With the discovery of a planetary system around TRAPPIST-1, there has been a surge of interest in ultracool dwarfs as potential planet hosts. Planetary systems around ultracool dwarfs represent our best chance of characterising temperate rocky-planet atmospheres with JWST. However, TRAPPIST-1 remains the only known system of its kind, and the occurrence rate of planets around ultracool dwarfs is still poorly constrained. We seek to perform a complete transit search on the ultracool dwarfs observed by NASA's K2 mission to constrain the occurrence rate of planets around these stars. We filter and characterise the sample of ultracool dwarfs observed by K2, by fitting their spectral energy distributions and using parallaxes from Gaia. We build an automatic pipeline to perform photometry, detrend the lightcurves, and search for transits. Using extensive injection-recovery tests of our pipeline, we compute the detection sensitivity of our search, and thus the completeness of our sample. We infer the planetary occurrence rates within a hierarchical Bayesian model (HBM) to treat uncertain planetary parameters. With the occurrence rate parametrised by a step-wise function, we show a convenient way to directly marginalise over the second level of our HBM (the planet parameters). Our method is applicable generally and can greatly speed up inference with larger catalogues of detected planets. We detect one planet in our sample of 702 ultracool dwarfs: a previously-validated mini-Neptune. We thus infer a mini-Neptune (2 - 4Re) occurrence rate of η = 0.20+0.16-0.11 within orbital periods of 1 - 20 days. For super-Earths (1 - 2Re) and ice/gas giants (4 - 6Re) within 1 - 20 days, we place 95% credible intervals of η < 1.14 and η < 0.29, respectively. If TRAPPIST-1-like systems were ubiquitous, we would have had a 96% chance of finding at least one.
