恒星表面transit成像的无模型逆方法：利用transit巡天绘制恒星点覆盖图
Model-free inverse method for transit imaging of stellar surfaces: Using transit surveys to map stellar spot coverage
摘要：
上下文我们提出了一个无模型的方法映射表面亮度变化。目标。我们的目标是发展一种方法，既不依赖于恒星大气模型，也不依赖于边缘暗化方程。这种方法是优化的系外行星过境调查，这样就可以创建一个大的数据库的恒星点覆盖范围。方法.该方法使用来自同一系统的几个凌日事件的光变曲线。这些光变曲线是相位折叠和中值组合的，以形成没有时间局部亮度变化的高质量光变曲线。使用无模型方法从该光变曲线中提取恒星比强度。我们搜索单个光变曲线，以寻找与中值组合光变曲线的偏离。这种偏离被解释为恒星表面的亮度变化。恒星表面的亮度变化图是通过寻找亮度分布来产生的，该亮度分布可以产生与观测结果很好拟合的合成光变曲线。没有对亮度变化的大小、形状或对比度做出任何假设。结果我们成功地再现了恒星盘的地图，从合成数据和档案观测FORS 2，视觉和近紫外FOcal还原器和低色散光谱仪的甚大望远镜（VLT）。
英文摘要：
Context. We present a model-free method for mapping surface brightness variations. Aims. We aim to develop a method that is not dependent on either stellar atmosphere models or limb-darkening equation. This method is optimized for exoplanet transit surveys such that a large database of stellar spot coverage can be created. Methods. The method uses light curves from several transit events of the same system. These light curves are phase-folded and median-combined to for a high-quality light curve without temporal local brightness variations. Stellar specific intensities are extracted from this light curve using a model-free method. We search individual light curves for departures from the median-combined light curve. Such departures are interpreted as brightness variations on the stellar surface. A map of brightness variations on the stellar surface is produced by finding the brightness distribution that can produce a synthetic light curve that fits observations well. No assumptions about the size, shape, or contrast of brightness variations are made. Results. We successfully reproduce maps of stellar disks from both synthetic data and archive observations from FORS2, the visual and near UV FOcal Reducer and low dispersion Spectrograph for the Very Large Telescope (VLT).
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