论文标题
恒星冠状X射线发射和表面磁通量
Stellar coronal X-ray emission and surface magnetic flux
论文作者
论文摘要
观察结果表明，太阳和其他恒星的冠状X射线发射取决于表面磁场。使用不同物理参数之间的幂律缩放关系，我们构建了一个分析模型，将观察到的X射线发射连接到磁通量。我们模型的基础是Rosner，Tucker \＆Vaiana（RTV）的缩放定律，它们将冠状环的温度和压力连接到其长度和能量输入。为了估计进入高层大气的能量通量，我们使用衍生得出的尺度来用于不同的加热机制，例如用于现场线编织或alfven波加热。我们通过观察到活动区域和磁通量之间的关系以及X射线发射率如何取决于温度的量表来补充这一点。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 _ {\ rm x} \ proptoφ^m $，幂律索引$ m $在大约1到2的范围内。此发现与众多的观察范围一致，来自太阳的各个特征，例如。明亮的点或活动区域，转向不同类型的恒星和不同水平的活动。幂律指数$ m $取决于加热机构的选择，而我们的结果略有利于与Alfvén波加热相比的编织和纳米层场景。此外，仪器的选择将对幂律指数$ m $ $ $产生影响，这是因为观察到的波长区域对冠状血浆温度的敏感性。总体而言，我们基于RTV缩放定律的简单分析模型可以很好地表示观察到的X射线发射。这强调了我们可能能够理解出色的冠状活动，这是一系列基本的构建基块，即循环，我们可以在太阳上以空间解决的细节进行研究。
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, $L_{\rm X}\propto Φ^m$, 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 Alfvén 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.
