外行星光变曲线中仪器系统学去趋势的盲法
A blind method to detrend instrumental systematics in exoplanetary light-curves
摘要：
对凌日系外行星大气层的研究需要$\sim 10^4$中一部分的测光精度和可重复性。这超出了当前天文台的原始校准计划，因此有必要从原始数据集中的天体物理信号中分离仪器系统学。文献中使用的大多数方法都是基于近似的仪器模型。模型参数的选择及其函数形式有时可能是主观的，在文献中引起争议。最近，Morello等人（2014，2015）开发了一种非参数去趋势方法，当应用于文献中争论的Spitzer/IRAC数据集时，该方法给出了一致和可重复的结果。所述方法基于单个像素时间序列的独立分量分析（ICA），下文称为"像素-ICA"。本文的主要目的是研究像素ICA在一系列具有不同仪器属性的模拟数据集上的局限性和优势，以及一系列抖动时间尺度和形状，非平稳性，突变点等。像素ICA的性能与其他方法进行了比较，特别是多项式质心分割（PCD），和像素级去相关（PLD）方法（Deming等人，2014）。我们发现，在模拟的情况下，像素ICA执行以及或优于其他方法，它也保证了更高程度的客观性，因为它的纯粹的统计基础，没有事先信息的仪器系统。结合Spitzer/IRAC数据集的分析，本文的结果表明，利用现有的红外空间仪器，$10^4$中一部分的测光精度和重复性是可以达到的。
英文摘要：
The study of the atmospheres of transiting exoplanets requires a photometric precision, and repeatability, of one part in $\sim 10^4$. This is beyond the original calibration plans of current observatories, hence the necessity to disentangle the instrumental systematics from the astrophysical signals in raw datasets. Most methods used in the literature are based on an approximate instrument model. The choice of parameters of the model and their functional forms can sometimes be subjective, causing controversies in the literature. Recently, Morello et al. (2014, 2015) have developed a non-parametric detrending method that gave coherent and repeatable results when applied to Spitzer/IRAC datasets that were debated in the literature. Said method is based on Independent Component Analysis (ICA) of individual pixel time-series, hereafter "pixel-ICA". The main purpose of this paper is to investigate the limits and advantages of pixel-ICA on a series of simulated datasets with different instrument properties, and a range of jitter timescales and shapes, non-stationarity, sudden change points, etc. The performances of pixel-ICA are compared against the ones of other methods, in particular polynomial centroid division (PCD), and pixel-level decorrelation (PLD) method (Deming et al. 2014). We find that in simulated cases pixel-ICA performs as well or better than other methods, and it also guarantees a higher degree of objectivity, because of its purely statistical foundation with no prior information on the instrument systematics. The results of this paper, together with previous analyses of Spitzer/IRAC datasets, suggest that photometric precision and repeatability of one part in $10^4$ can be achieved with current infrared space instruments.
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