标题： 基于PSF的方法处理开普勒/K2数据。 I. K2第0轮观测中星团M 35和NGC 2158内的变异性 显示英文标题

标题： A PSF-based approach to Kepler/K2 data. I. Variability within the K2 Campaign 0 star clusters M 35 and NGC 2158

摘要： 开普勒和K2数据的分析在文献中大多是基于孔径测光法。 由于开普勒的大尺寸、欠采样的像素以及附近天体的存在，孔径测光法并不总是获得高精度测光的理想方法，因此到目前为止，该数据集尚未被充分利用。 我们提出了一种新方法，该方法基于我们在欠采样哈勃望远镜图像方面的经验。 该方法涉及点扩散函数（PSF）邻近天体减法，并专门开发用于利用K2“超级快照”在密集星团核心区域提供的巨大潜力。 我们的测试目标是K2第0次观测活动期间观测到的NGC 2158和M 35区域。 我们展示了我们的PSF建模，并证明通过使用来自阿西亚戈施密特望远镜的高角分辨率输入恒星列表作为PSF邻近天体减法的基础，即使在最密集的区域，我们也能达到Kp~24的亮度，6.5小时内测光精度为10%。 在明亮端，我们的测光精度达到约30百万分之一。 与传统的孔径测光法相比，我们的方法在较暗的亮度（Kp>15.5）上实现了显著的改进。 这种改进在拥挤区域更为明显。 我们还提取了约60,000颗恒星的原始光变曲线，并对其进行了去趋势处理，以消除由航天器运动和其他损害K2测光精度的伪影引起的系统效应。 我们提供了一个包含2133个变星的列表。 显示英文摘要

摘要： Kepler and K2 data analysis reported in the literature is mostly based on aperture photometry. Because of Kepler's large, undersampled pixels and the presence of nearby sources, aperture photometry is not always the ideal way to obtain high-precision photometry and, because of this, the data set has not been fully exploited so far. We present a new method that builds on our experience with undersampled HST images. The method involves a point-spread function (PSF) neighbour-subtraction and was specifically developed to exploit the huge potential offered by the K2 "super-stamps" covering the core of dense star clusters. Our test-bed targets were the NGC 2158 and M 35 regions observed during the K2 Campaign 0. We present our PSF modeling and demonstrate that, by using a high-angular-resolution input star list from the Asiago Schmidt telescope as the basis for PSF neighbour subtraction, we are able to reach magnitudes as faint as Kp~24 with a photometric precision of 10% over 6.5 hours, even in the densest regions. At the bright end, our photometric precision reaches ~30 parts-per-million. Our method leads to a considerable level of improvement at the faint magnitudes (Kp>15.5) with respect to the classical aperture photometry. This improvement is more significant in crowded regions. We also extracted raw light curves of ~60,000 stars and detrended them for systematic effects induced by spacecraft motion and other artifacts that harms K2 photometric precision. We present a list of 2133 variables.