TFAW调查。I.基于小波的K2光变曲线去噪。在K2第一次活动中发现和验证两颗新的地球大小的行星
TFAW survey. I. Wavelet-based denoising of K2 light curves. Discovery and validation of two new Earth-sized planets in K2 campaign 1
摘要：
基于小波的去趋势和去噪方法\texttt{TFAW}首次应用于\texttt{EVEREST 2.0}校正的光变曲线，以进一步提高几乎所有K2观测活动（C1-C8，C12-C18）的光度精度。这两种方法的性能进行评估，在6小时的联合差分测光精度（CDPP），模拟过境检测效率，和行星表征在不同的SNR制度。平均而言，在所有观察活动中，\texttt{TFAW}中位6小时CDPP为$\sim$ 30 $\%$，优于\texttt{EVEREST 2.0}。使用\texttt{transit least-squares}（\texttt{TLS}）算法，我们表明，模拟地球-太阳系统的过境检测效率是$\sim$ 8.5 $\times$高\texttt{TFAW}校正的光变曲线比\texttt{EVEREST 2.0}的。使用两个已确认的系外行星，K2-44 b（高信噪比）和K2-298 b（低信噪比）的光变曲线，我们表明，\texttt{TFAW}产生更好的MCMC后验分布，凌日参数与编目的兼容，但具有较小的不确定性和缩小的可信区间。我们使用\texttt{TFAW}的测光精度的提高和\texttt{TLS}的信号检测效率的增强相结合，以寻找新的过境候选人在K2观测活动1。我们报告发现了两个新的K2-C1地球大小的行星，使用\texttt{vespa}软件进行统计验证：EPIC 201170410.02，半径为1.047 $^{+0.276}_{-0.257}R_{\oplus}$行星绕M型恒星旋转，EPIC 201757695.02，半径为0.908 $^{+0.059}_{-0.064}R_{\oplus}$行星绕K型恒星旋转。EPIC 201757695.02是K2-C1中发现的第9小行星，也是所有K2活动中第39小的行星。
英文摘要：
The wavelet-based detrending and denoising method \texttt{TFAW} is applied for the first time to \texttt{EVEREST 2.0}-corrected light curves to further improve the photometric precision of almost all K2 observing campaigns (C1-C8, C12-C18). The performance of both methods is evaluated in terms of 6 hr combined differential photometric precision (CDPP), simulated transit detection efficiency, and planet characterization in different SNR regimes. On average, \texttt{TFAW} median 6hr CDPP is $\sim$30$\%$ better than the one achieved by \texttt{EVEREST 2.0} for all observing campaigns. Using the \texttt{transit least-squares} (\texttt{TLS}) algorithm, we show that the transit detection efficiency for simulated Earth-Sun-like systems is $\sim$8.5$\times$ higher for \texttt{TFAW}-corrected light curves than for \texttt{EVEREST 2.0} ones. Using the light curves of two confirmed exoplanets, K2-44 b (high-SNR) and K2-298 b (low-SNR), we show that \texttt{TFAW} yields better MCMC posterior distributions, transit parameters compatible with the cataloged ones but with smaller uncertainties and narrows the credibility intervals. We use the combination of \texttt{TFAW}'s improved photometric precision and \texttt{TLS} enhancement of the signal detection efficiency for weak signals to search for new transit candidates in K2 observing campaign 1. We report the discovery of two new K2-C1 Earth-sized planets statistically validated, using the \texttt{vespa} software: EPIC 201170410.02, with a radius of 1.047$^{+0.276}_{-0.257}R_{\oplus}$ planet orbiting an M-type star, and EPIC 201757695.02, with a radius of 0.908$^{+0.059}_{-0.064}R_{\oplus}$ planet orbiting a K-type star. EPIC 201757695.02 is the 9-th smallest planet ever discovered in K2-C1, and the 39-th smallest in all K2 campaigns.
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