论文标题
星空的3D辐射MHD模拟
3D Radiative MHD simulations of starspots
论文作者
论文摘要
除了太阳以外的恒星上没有直接解决斑点的直接分辨观察结果，而星空特性则通过灯弯曲和光谱极化数据间接推断。我们介绍了G2V，K0V和M0V恒星上星状点的第一个自一致的3D辐射MHD计算，这将有助于更好地了解晚期主序列中的活动，可变性和磁场的观察。我们使用了穆拉姆代码，该代码已广泛用于计算“现实”黑子，以进行我们的模拟。我们旨在研究基本的星点特性，例如强度对比度，温度和磁场强度随频谱类型而变化。我们首先在2D中模拟了每种光谱类型的多个斑点，以找出适合我们3D运行的初始条件。我们发现，随着恒星有效温度的升高，该点及其周围光球的温度差异从M0V恒星的350K到G2V恒星的1400K。我们模拟的星空中的这种趋势与观察结果一致。所有星形象征的磁场强度均在3-4.5千克范围内。 G2V和K0V Umbrae的磁场强度约为3.5 kg，而M0V UMBRA的磁场强度相对较高。我们讨论了这两种趋势背后的物理原因。所有三个星空都会形成带有evershed流的半纤维丝状结构。在G2V PENUMBRA中，平均Evershed流速从1.32 km S $^{ - 1} $下降到M0V Penumbra中的0.6 km S $^{ - 1} $。
There are no direct spatially resolved observations of spots on stars other than the Sun and starspot properties are inferred indirectly through lightcurves and spectropolarimetric data. We present the first self-consistent 3D radiative MHD computations of starspots on G2V, K0V and M0V stars, which will help to better understand observations of activity, variability and magnetic fields in late-type main-sequence stars. We used the MURaM code, which has been extensively used to compute "realistic" sunspots, for our simulations. We aim to study how fundamental starspot properties such as intensity contrast, temperature and magnetic field strength vary with spectral type. We first simulated in 2D, multiple spots of each spectral type to find out appropriate initial conditions for our 3D runs. We find that with increasing stellar effective temperature, there is an increase in the temperature difference between the umbra of the spot and its surrounding photosphere, from 350K on the M0V star to 1400K on the G2V star. This trend in our simulated starspots is consistent with observations. The magnetic field strengths of all the starspot umbrae are in the 3-4.5 kG range. The G2V and K0V umbrae have comparable magnetic field strengths around 3.5 kG, while the M0V umbra has a relatively higher field strength around 4 kG. We discuss the physical reasons behind both these trends. All of the three starspots develop penumbral filament-like structures with Evershed flows. The average Evershed flow speed drops from 1.32 km s$^{-1}$ in the G2V penumbra to 0.6 km s$^{-1}$ in the M0V penumbra.
