[论文解读] High-resolution imaging of $Kepler$ planet host candidates. A comprehensive comparison of different techniques

J. Lillo-Box, D. Barrado+1 more|arXiv (Cornell University)|May 13, 2014

Stellar, planetary, and galactic studies参考文献 35被引用 63

一句话总结

本研究利用位于卡拉斯托天文台的AstraLux North仪器对174颗开普勒行星候选体宿主恒星进行高分辨率幸运成像，以评估其多重性及污染风险。研究发现67.2%的宿主恒星为孤立源，32.8%在6角秒内存在伴星（其中17.2%在3角秒内）；识别出三个因混合双星导致的假阳性行星候选体，并提出混合源置信度（BSC）参数以量化假阳性概率，从而提升行星验证效率与后续观测优先级。

ABSTRACT

The Kepler mission has discovered thousands of planet candidates. Currently, some of them have already been discarded; more than 200 have been confirmed by follow-up observations, and several hundreds have been validated. However, most of them are still awaiting for confirmation. Thus, priorities (in terms of the probability of the candidate being a real planet) must be established for subsequent observations. The motivation of this work is to provide a set of isolated (good) host candidates to be further tested by other techniques. We identify close companions of the candidates that could have contaminated the light curve of the planet host. We used the AstraLux North instrument located at the 2.2 m telescope in the Calar Alto Observatory to obtain diffraction-limited images of 174 Kepler objects of interest. The lucky-imaging technique used in this work is compared to other AO and speckle imaging observations of Kepler planet host candidates. We define a new parameter, the blended source confidence level (BSC), to assess the probability of an object to have blended non-detected eclipsing binaries capable of producing the detected transit. We find that 67.2% of the observed Kepler hosts are isolated within our detectability limits, and 32.8% have at least one visual companion at angular separations below 6 arcsec. We find close companions (below 3 arcsec) for the 17.2% of the sample. The planet properties of this sample of non-isolated hosts are revised. We report one possible S-type binary (KOI-3158). We also report three possible false positives (KOIs 1230.01, 3649.01, and 3886.01) due to the presence of close companions. The BSC parameter is calculated for all the isolated targets and compared to both the value prior to any high-resolution image and, when possible, to observations from previous high-spatial resolution surveys in the Kepler sample.

研究动机与目标

• 识别在6角秒内无近距离伴星、污染风险较低的开普勒行星宿主候选体，以优先开展视向速度后续观测。
• 探测可能因混合食双星而模拟出行星凌星信号的近距离光学伴星。
• 利用高空间分辨率成像验证或修正行星候选体的物理参数。
• 提出并应用混合源置信度（BSC）参数，以量化假阳性概率。
• 比较幸运成像结果与其他高分辨率技术（自适应光学、光斑成像）在开普勒样本中的表现。

提出的方法

• 使用位于卡拉斯托天文台2.2米望远镜上的AstraLux North仪器进行高分辨率幸运成像。
• 该技术实现了衍射极限成像，可探测至3角秒角距离的伴星。
• 定义了一项新指标——混合源置信度（BSC），用于估算未被探测到的食双星对光曲线造成污染的概率。
• 将174颗开普勒天体兴趣目标（KOIs）与174颗被剔除的KOIs（行星候选体被拒绝）组成的对照样本进行比较。
• 将成像结果与先前的高空间分辨率巡天及开普勒光度数据交叉匹配，以评估污染程度。
• 通过分析伴星的光度和天体测量特性，评估如S型双星等轨道构型。

实验结果

研究问题

• RQ1 在6角秒内无近距离伴星的开普勒行星宿主候选体占多大比例，表明其污染风险较低？
• RQ2 在开普勒样本中，不同高分辨率成像技术（幸运成像、自适应光学、光斑成像）的结果如何比较？
• RQ3 哪些行星候选体可能因混合食双星而为假阳性？其修正后的参数有何不同？
• RQ4 近距离伴星在多大程度上改变了开普勒候选体的推导行星参数？
• RQ5 新定义的混合源置信度（BSC）参数在量化假阳性概率方面效果如何？

主要发现

• 在174个观测到的开普勒宿主恒星中，67.2%在探测极限内为孤立源，表明来自混合源的污染风险较低。
• 样本中32.8%的恒星在6角秒内至少存在一个光学伴星，其中17.2%在3角秒内存在伴星。
• 三颗行星候选体（KOI-1230.01、KOI-3649.01、KOI-3886.01）因无法分辨的近距离伴星被识别为可能的假阳性。
• 一个系统（KOI-3158）可能为S型双星，其中五颗行星候选体可能围绕一对近距离双星中的一个成员运行。
• 混合源置信度（BSC）参数成功量化了假阳性概率，并改善了验证统计结果。
• 本研究证实，高分辨率成像对准确估计行星参数和验证行星性质至关重要，尤其对小行星而言。