TIGRE太阳S指数与USET Ca II K全日面图像之间的关系
Relationship between TIGRE solar S-index and USET Ca II K full disk images
AI总结：
本文利用USET Ca II K全日面图像推导色球亮结构面积占比，发现其与TIGRE S指数呈紧密线性关系，证明日面覆盖率可作为S指数的有效代理指标，并可用于研究太阳型恒星自转周期与磁活动。
摘要：
在Ca II K谱线中对太阳色球进行的全日面观测，是研究太阳磁活动的一类宝贵数据集。S指数被广泛用于研究恒星的磁活动，然而它与恒星磁结构覆盖范围之间的联系目前仍不清楚。我们利用比利时皇家天文台使用USET拍摄的全日面Ca II K图像档案，推导了过去十年中最亮色球结构的面积占比。这些数据使我们能够研究第24太阳活动周的结束和第25太阳活动周的开始。随后，使用基于强度阈值的算法对太阳表面最亮区域进行了分割。我们计算了其在太阳日面上的面积占比，并将其与来自TIGRE的S指数进行了比较。为了检测周期性调制，我们对两个数据集都应用了离散傅里叶功率谱方法。结果发现，USET面积占比与TIGRE S指数之间存在紧密的线性关系，并且在低活动水平状态下，通过考虑增强网络可以获得更好的相关性。在两个时间序列中，我们都检测到了由太阳日面上亮结构旋转引起的调制。然而，由于TIGRE的观测策略，这种检测在其数据中受到限制。我们研究了在十年重叠期内色球结构日面覆盖率与S指数变化之间的相关性。我们得出结论，日面覆盖率指数是S指数的一个良好代理指标，并将在未来对太阳型恒星磁活动的研究中发挥作用。USET面积占比数据集最适合用于评估太阳自转周期，并将在未来的工作中用于分析恒星自转轴倾角对在太阳型恒星中检测此类周期性调制的影响。
英文摘要：
Full disk observations of the solar chromosphere in the Ca II K line represent a valuable dataset for studies of solar magnetic activity. The S-index is widely used to investigate the magnetic activity of stars, however, its connection to the coverage of stellar magnetic structure is still poorly understood. We use the archives of full disk Ca II K images taken by the Royal Observatory of Belgium with the USET to derive the area fraction of the brightest chromospheric structures over the last decade. These data allowed us to study the end of the solar cycle 24 and the beginning of solar cycle 25. The brightest regions of the solar surface were then segmented using an algorithm based on an intensity threshold. We computed the area fraction over the solar disk and compared it with the S-index from TIGRE. For the detection of periodic modulations, we applied a discrete Fourier power spectrum method to both datasets. A tight linear relationship was found between the USET area fraction and the TIGRE S-index, with an improved correlation obtained in the low-activity regime by considering the enhanced network. In both time series, we detected the modulation caused by the rotation of bright structures on the solar disk. However, this detection is constrained in the case of TIGRE due to its observation strategy. We studied the correlation between the disk coverage with chromospheric structures and the variability of the S-index on an overlapping period of ten years. We concluded that the disk coverage index is a good proxy for the S-index and will be useful in future studies of the magnetic activity of solar-type stars. The USET area fraction dataset is most appropriate for evaluating the solar rotation period and will be used in future works to analyze the impact of the inclination of the stellar rotation axis on the detectability of such periodic modulations in solar-type stars.
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