探测北极星令人困惑的径向速度信号：脉动（不）稳定性、轨道运动和平分线变化
Probing Polaris' Puzzling Radial Velocity Signals - Pulsational (In-)Stability, Orbital Motion, and Bisector Variations
摘要：
我们调查随时间变化的变化幅度和多周期性的I型造父北极星使用161高精度的径向速度（RV）和平分线反跨度（BIS）测量的基础上，使用Hermes在1.2米佛兰芒墨卡托望远镜在西班牙加那利群岛的拉帕尔马记录的光谱。使用经验模板拟合方法，我们表明Polaris的RV振幅在2011年9月至2018年11月期间一直稳定在$\sim 30 \rm{m s}^{-1}$范围内。我们应用模板拟合方法公开访问，同质RV数据集从文献中，并提供了一个更新的解决方案北极星偏心29.3年的轨道。虽然推断的脉动诱导的RV振幅不同的个人数据集，我们发现没有证据的时间变量RV振幅在任何单独考虑，均匀的数据集。此外，我们发现，增加光度振幅确定使用SMEI光度可能是虚假的检测，由于尚未了解系统的影响，仪器的起源。鉴于这种令人困惑的情况，需要进一步分析具有良好理解的系统学的高质量同质数据集，以自信地确定北极星的变异幅度是否会随着时间的推移而变化。我们确认周期性平分线的变化周期为3.97天和40.22天，使用Hermes BIS测量，并确定在60.17天的周期第三个信号。虽然60.17 d信号在BIS周期图中占主导地位，但我们注意到该信号可能与40.22 d信号无关。最后，我们证明了40.22 d信号不能用恒星自转来解释。需要进一步的长期，高质量的光谱监测来解开北极星周期信号的完整集合，这有可能为造父变星的演变提供前所未有的见解。
英文摘要：
We investigate temporally changing variability amplitudes and the multi-periodicity of the type-I Cepheid Polaris using 161 high-precision radial velocity (RV) and bisector inverse span (BIS) measurements based on optical spectra recorded using Hermes at the 1.2 m Flemish Mercator telescope on La Palma, Canary Islands, Spain. Using an empirical template fitting method, we show that Polaris' RV amplitude has been stable to within $\sim 30 \rm{m s}^{-1}$ between September 2011 and November 2018. We apply the template fitting method to publicly accessible, homogeneous RV data sets from the literature and provide an updated solution of Polaris' eccentric 29.3 yr orbit. While the inferred pulsation-induced RV amplitudes differ among individual data sets, we find no evidence for time-variable RV amplitudes in any of the separately considered, homogeneous data sets. Additionally, we find that increasing photometric amplitudes determined using SMEI photometry are likely spurious detections due to as yet ill-understood systematic effects of instrumental origin. Given this confusing situation, further analysis of high-quality homogeneous data sets with well-understood systematics is required to confidently establish whether Polaris' variability amplitude is subject to change over time. We confirm periodic bisector variability periods of 3.97 d and 40.22 d using Hermes BIS measurements and identify a third signal at a period of 60.17 d. Although the 60.17 d signal dominates the BIS periodogram, we caution that this signal may not be independent of the 40.22 d signal. Finally, we show that the 40.22 d signal cannot be explained by stellar rotation. Further long-term, high-quality spectroscopic monitoring is required to unravel the complete set of Polaris' periodic signals, which has the potential to provide unprecedented insights into the evolution of Cepheid variables.
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