对Eps Ind A看不见的伴星的成像搜索--用4微米观测提高探测极限
Imaging search for the unseen companion to Eps Ind A -- Improving the detection limits with 4 micron observations
摘要：
Eps Ind A是最近的类太阳恒星之一，距离我们只有3.6 pc。已知它拥有一颗双星褐矮星伴星Eps Ind Ba/Bb，预计距离为6.7”，但径向速度测量意味着系统中存在一个额外的，但看不见的组件，更接近Eps Ind A。先前的直接成像已经排除了任何恒星或高质量棕矮星伴星的存在，表明看不见的伴星可能是低质量棕矮星或高质量行星。我们提出了一个深的高对比度成像搜索的同伴，使用主动角差分成像（aADI）在4微米，一个特别强大的技术，在附近和相对较老的恒星周围的行星搜索的结果。我们还开发了一个额外的PSF参考减法方案的基础上局部优化的图像组合（LOCI），以进一步提高检测限。在图像中没有看到伴星，尽管我们对比以前获得的质量明显更低的质量很敏感。结合成像数据和已知的径向速度趋势，我们将伴星的性质限制在大约5-20 Mjup，10-20 AU，i > 20 deg，除非它是一个奇异的恒星残骸。结果还表明，该系统可能比通常假设的~1 Gyr年龄更老。
英文摘要：
Eps Ind A is one of the nearest sun-like stars, located only 3.6 pc away. It is known to host a binary brown dwarf companion, Eps Ind Ba/Bb, at a large projected separation of 6.7", but radial velocity measurements imply that an additional, yet unseen component is present in the system, much closer to Eps Ind A. Previous direct imaging has excluded the presence of any stellar or high-mass brown dwarf companion at small separations, indicating that the unseen companion may be a low-mass brown dwarf or high-mass planet. We present the results of a deep high-contrast imaging search for the companion, using active angular differential imaging (aADI) at 4 micron, a particularly powerful technique for planet searches around nearby and relatively old stars. We also develop an additional PSF reference subtraction scheme based on locally optimized combination of images (LOCI) to further enhance the detection limits. No companion is seen in the images, although we are sensitive to significantly lower masses than previously achieved. Combining the imaging data with the known radial velocity trend, we constrain the properties of the companion to within approximately 5-20 Mjup, 10-20 AU, and i > 20 deg, unless it is an exotic stellar remnant. The results also imply that the system is probably older than the frequently assumed age of ~1 Gyr.
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