论文标题
M Dwarf星的全球趋势
Global trends in winds of M dwarf stars
论文作者
论文摘要
M矮人恒星目前是寻找潜在可居住行星的主要目标。但是，他们的风被认为对行星气氛有害。在这里，为了更好地了解M矮人的风并推断其物理特性，我们对M矮人的风进行了一维的磁性水力学参数研究，这些参数通过alfvén波的耗散而加热。这些波是由地下对流运动触发的，并沿磁场线传播。在这里，我们在风库（染色体球）处改变了磁场强度和密度，同时保持相同的相对波幅度（$ 0.1 B_0 $）和耗散lenghtscale。我们发现，我们的风很快达到等温温度，质量损失率与基础密度平方成正比。我们将结果与帕克风模型进行了比较，发现在高β政权中，这两个模型都同意。然而，在低β型制度中，帕克风将终端速度低于一个数量级和质量损失率的速度下降了几个数量级。我们还发现，M矮人可能具有延伸到恒星半径的18％至180％的色球球体。我们将模型应用于行星托管星GJ 436，从X射线观测约束中找到$ \ dot {m} <7.6 \ times 10^{ - 15} \，m _ {\ odot}〜\ text}这与GJ 436B的Lyman-Alpha Transit得出的值一致，这表明光谱行星转移可以用作研究恒星风质的一种方式。
M dwarf stars are currently the main targets in searches for potentially habitable planets. However, their winds have been suggested to be harmful to planetary atmospheres. Here, in order to better understand the winds of M dwarfs and also infer their physical properties, we perform a one-dimensional magnetohydrodynamic parametric study of winds of M dwarfs that are heated by dissipation of Alfvén waves. These waves are triggered by sub-surface convective motions and propagate along magnetic field lines. Here, we vary the magnetic field strength and density at the wind base (chromosphere), while keeping the same relative wave amplitude ($0.1 B_0$) and dissipation lenghtscale. We find that our winds very quickly reach isothermal temperatures with mass-loss rates proportional to base density square. We compare our results with Parker wind models and find that, in the high-beta regime, both models agree. However, in the low-beta regime, the Parker wind underestimates the terminal velocity by around one order of magnitude and mass-loss rate by several orders of magnitude. We also find that M dwarfs could have chromospheres extending to 18% to 180% of the stellar radius. We apply our model to the planet-hosting star GJ 436 and find, from X-ray observational constraints, $\dot{M}<7.6\times 10^{-15}\,M_{\odot}~\text{yr}^{-1}$. This is in agreement with values derived from the Lyman-alpha transit of GJ 436b, indicating that spectroscopic planetary transits could be used as a way to study stellar wind properties.
