K-Stacker：用于直接探测系外行星的开普勒图像重组
K-Stacker: Keplerian image recombination for the direct detection of exoplanets
摘要：
我们提出了一个新的算法，可用于检测高对比度图像中的系外行星的概念证明。该算法适当地结合了在不同夜晚获得的多个观测数据，同时考虑到行星的轨道运动。方法.我们模拟SPHERE/IRDIS观测的时间序列，其中我们在随机轨道上盲目地注入行星，随机S/N水平，低于检测限（S/N 1.5）。然后，我们使用优化算法来猜测轨道参数，并考虑到轨道运动，以适当地重组不同的图像，并最终检测到行星。我们表明，优化算法确实可以用来找到未检测到的行星在时间序列的图像，即使它们分布在轨道的时间尺度。正如预期的那样，信噪比的典型增益是sqrt（n），n是合并的观测数。我们发现，K-Stacker算法能够脱轨并结合图像，以达到类似于行星不移动时所预期的性能水平。我们发现S/N=5时的回收率为50%。我们还发现，该算法能够以一个像素的精度确定行星在各个帧中的位置，即使行星本身在每个帧中低于检测限。我们的模拟表明，K-Stacker可用于提高当前系外行星成像仪器的对比度极限，并发现较暗的天体。我们还建议，K-Stacker在时间序列的每一张图像中确定行星位置的能力可以用作新观测策略的一部分，在这种策略中，长时间曝光将被分解为几个月内的较短曝光。这就有可能确定行星的轨道参数，而不需要多次高S/N > 5的探测。
英文摘要：
We present a proof of concept for a new algorithm which can be used to detect exoplanets in high contrast images. The algorithm properly combines mutliple observations acquired during different nights, taking into account the orbital motion of the planet. Methods. We simulate SPHERE/IRDIS time series of observations in which we blindly inject planets on random orbits, at random level of S/N, below the detection limit (down to S/N 1.5). We then use an optimization algorithm to guess the orbital parameters, and take into account the orbital motion to properly recombine the different images, and eventually detect the planets. We show that an optimization algorithm can indeed be used to find undetected planets in temporal sequences of images, even if they are spread over orbital time scales. As expected, the typical gain in S/N ratio is sqrt(n), n being the number of observations combined. We find that the K-Stacker algorithm is able de-orbit and combine the images to reach a level of performance similar to what could be expected if the planet was not moving. We find recovery rates of 50% at S/N=5. We also find that the algorithm is able to determine the position of the planet in individual frames at one pixel precision, even despite the fact that the planet itself is below the detection limit in each frame. Our simulations show that K-Stacker can be used to increase the contrast limit of current exoplanet imaging instruments and to discover fainter bodies. We also suggest that the ability of K-Stacker to determine the position of the planet in every image of the time serie could be used as part of a new observing strategy in which long exposures would be broken into shorter ones spread over months. This could make possible to determine the orbital parameters of a planet without requiring multiple high S/N > 5 detections.
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