Stellar coronal X-ray emission and surface magnetic flux
Stellar coronal X-ray emission and surface magnetic flux
复制标题
恒星日冕X射线发射和表面磁通量
DOI：
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
H. Peter
中科院分区：
文献类型：
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作者：
J. Zhuleku;J. Warnecke;H. Peter
观测表明，太阳和其他恒星的日冕X射线发射取决于表面磁场。利用不同物理参数之间的幂律标度关系，我们建立了一个分析模型，将观测到的 X 射线发射与磁通量联系起来。我们模型的基础是 Rosner、Tucker 和 Vaiana (RTV) 的标度定律，它将日冕环的温度和压力与其长度和能量输入联系起来。为了估计进入高层大气的能量通量，我们使用针对不同加热机制得出的标度，例如用于现场线编织或阿尔文波加热。我们通过观察活动区域大小和磁通量之间的关系来补充这一点，并得出 X 射线发射率如何依赖于温度的比例。根据我们的分析模型，我们发现 X 射线发射对磁通量的幂律依赖性，$L_{
m X}propto Phi^m$，幂律指数 $m$ 的范围约为 1 到 2。这一发现与来自太阳各个特征的广泛观察结果一致，例如亮点或活动区域，不同类型和不同活动水平的恒星。幂律指数 $m$ 取决于加热机制的选择，我们的结果稍微偏向于编织和纳米耀斑场景而不是阿尔文波加热。此外，仪器的选择也会对幂律指数$m$产生影响，这是因为观测波长区域对日冕等离子体温度的敏感性。总体而言，我们基于 RTV 缩放定律的简单分析模型很好地表示了观察到的 X 射线发射。这强调我们也许能够通过一系列基本构建块（即环）来理解恒星日冕活动，我们可以在太阳上研究空间分辨的细节。
Observations show that the coronal X-ray emission of the Sun and other stars depends on the surface magnetic field. Using power-law scaling relations between different physical parameters, we build an analytical model to connect the observed X-ray emission to the magnetic flux. The basis for our model are the scaling laws of Rosner, Tucker & Vaiana (RTV) that connect the temperature and pressure of a coronal loop to its length and energy input. To estimate the energy flux into the upper atmosphere, we use scalings derived for different heating mechanisms, e.g. for field-line braiding or Alfven-wave heating. We supplement this by observed relations between active region size and magnetic flux and derive scalings of how X-ray emissivity depends on temperature. Based on our analytical model, we find a power-law dependence of the X-ray emission on the magnetic flux, $L_{
m X}propto Phi^m$, with a power-law index $m$ being in the range from about 1 to 2. This finding is consistent with a wide range of observations, from individual features on the Sun, e.g. bright points or active regions, to stars of different types and varying levels of activity. The power-law index $m$ depends on the choice of the heating mechanism, and our results slightly favour the braiding and nanoflare scenarios over Alfven wave heating. In addition, the choice of instrument will have an impact on the power-law index $m$, which is because of the sensitivity of the observed wavelength region to the temperature of the coronal plasma. Overall, our simple analytical model based on the RTV scaling laws gives a good representation of the observed X-ray emission. This underlines that we might be able to understand stellar coronal activity though a collection of basic building blocks, i.e. loops, that we can study in spatially resolved detail on the Sun.
轮换与活动关系的广义研究：支持轮换周期而不是罗斯比数
DOI：
10.1088/0004-637x/794/2/144
发表时间：
2014
期刊：
The Astrophysical Journal
影响因子：
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作者：
Reiners;Schüssler;Passegger
通讯作者：
Passegger