Into the Depths: A New Activity Metric for High-precision Radial Velocity Measurements Based on Line Depth Variations
Into the Depths: A New Activity Metric for High-precision Radial Velocity Measurements Based on Line Depth Variations
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DOI：
10.3847/1538-3881/ac609a
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发表时间：
2022-04
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通讯作者：
Jared C. Siegel;R. Rubenzahl;S. Halverson;A. Howard
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作者：
Jared C. Siegel;R. Rubenzahl;S. Halverson;A. Howard
利用径向速度（RV）测量发现和表征系外行星受到来自主星表面噪声源的限制。目前抑制恒星磁活动的技术依赖于使用活动指示器（例如，Ca ii线的强度，相互关联函数的宽度，宽带测光）的去相关，或者仅使用已被证明对活动不敏感的光谱线的子集来测量rv。在这里，我们结合上述技术，使用Dumusque（2018）的“逐行”方法，从对活动最敏感的光谱线构建高信噪比活动指标，即深度度量(t)。类似于RV的光度去相关或活动指数的高斯进展回归建模，(t)的时间序列建模降低了RV测量中的磁活动幅度；在HARPS的αCenB RV时间序列中，RV均方根从2.67减小到1.02 ms−1。(t)模型使我们能够表征小至1 m s - 1的注入行星信号。在降噪和注入信号恢复方面，(t)建模通过选择对活动不敏感的谱线优于活动缓解。对于具有m s−1级活动信号的类太阳恒星，深度度量独立跟踪旋转调制和多年恒星活动，其质量水平与CCF的FWHM和log RHK '相似。深度度量及其详细说明将是减轻恒星磁活动的有力工具，特别是作为将恒星活动与宿主恒星内的物理过程联系起来的一种手段。
The discovery and characterization of extrasolar planets using radial velocity (RV) measurements is limited by noise sources from the surfaces of host stars. Current techniques to suppress stellar magnetic activity rely on decorrelation using an activity indicator (e.g., strength of the Ca ii lines, width of the cross-correlation function, broadband photometry) or measurement of the RVs using only a subset of spectral lines that have been shown to be insensitive to activity. Here, we combine the above techniques by constructing a high-signal-to-noise activity indicator, the depth metric (t) , from the most activity-sensitive spectral lines using the “line-by-line” method of Dumusque (2018). Analogous to photometric decorrelation of RVs or Gaussian progress regression modeling of activity indices, time series modeling of (t) reduces the amplitude of magnetic activity in RV measurements; in an αCenB RV time series from HARPS, the RV rms was reduced from 2.67 to 1.02 m s−1. (t) modeling enabled us to characterize injected planetary signals as small as 1 m s−1. In terms of noise reduction and injected signal recovery, (t) modeling outperforms activity mitigation via the selection of activity-insensitive spectral lines. For Sun-like stars with activity signals on the m s−1 level, the depth metric independently tracks rotationally modulated and multiyear stellar activity with a level of quality similar to that of the FWHM of the CCF and log RHK′ . The depth metric and its elaborations will be a powerful tool in the mitigation of stellar magnetic activity, particularly as a means of connecting stellar activity to physical processes within host stars.