恒星多普勒噪声的增强模型揭示了巨蟹座55的13年活动周期的暗示
Enhanced models for stellar Doppler noise reveal hints of a 13-year activity cycle of 55 Cancri
摘要：
我们考虑多普勒噪声模型的外行星径向速度拟合的统计鲁棒性的影响。我们表明，传统的模型的多普勒噪声与加性抖动可以产生大的非线性效应，降低了拟合的可靠性，特别是在涉及到corrected多普勒噪声的情况下。我们引入了加性噪声模型的正则化，可以优雅地消除其奇异性以及相关的非线性效应。我们应用这种方法的多普勒时间序列数据的几个系外行星系统。它表明，我们新的正则化噪声模型产生的轨道拟合，增加或至少相同的统计鲁棒性，与简单的加性抖动相比。参数估计中的各种统计不确定性往往会减少，而行星检测的意义往往会增加。关于55 CNC五行星系统，我们表明，它的多普勒数据包含显着的相关（“红色”）噪声。它的相关时间尺度从几天到几个月不等，其大小远大于行星N体扰动对径向速度的影响（这些扰动因此看起来无法检测到）。红噪声的特征取决于摄谱仪/天文台，并且还显示出与公共Ca II H & K和测光测量相位的周期性时间变化。我们将这种调制解释为55 Cnc长期活动周期的暗示，类似于太阳的11年周期。我们用$12.6\pm^{2.5}_{1.0}$年来估计55 Cnc活动期，最接近的最小值预计在2014年或2015年。
英文摘要：
We consider the impact of Doppler noise models on the statistical robustness of the exoplanetary radial-velocity fits. We show that the traditional model of the Doppler noise with an additive jitter can generate large non-linearity effects, decreasing the reliability of the fit, especially in the cases when a correleated Doppler noise is involved. We introduce a regularization of the additive noise model that can gracefully eliminate its singularities together with the associated non-linearity effects. We apply this approach to Doppler time-series data of several exoplanetary systems. It demonstrates that our new regularized noise model yields orbital fits that have either increased or at least the same statistical robustness, in comparison with the simple additive jitter. Various statistical uncertainties in the parametric estimations are often reduced, while planet detection significance is often increased. Concerning the 55 Cnc five-planet system, we show that its Doppler data contain significant correlated ("red") noise. Its correlation timescale is in the range from days to months, and its magnitude is much larger than the effect of the planetary N-body perturbations in the radial velocity (these perturbations thus appear undetectable). Characteristics of the red noise depend on the spectrograph/observatory, and also show a cyclic time variation in phase with the public Ca II H & K and photometry measurements. We interpret this modulation as a hint of the long-term activity cycle of 55 Cnc, similar to the Solar 11-year cycle. We estimate the 55 Cnc activity period by $12.6\pm^{2.5}_{1.0}$ yrs, with the nearest minimum presumably expected in 2014 or 2015.
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