arXiv 2004.029042020-04-06astro-ph.SRastro-ph.EP

M型矮星X射线活度与自转的关系及X射线亮度的时间演化预测

Relation of X-ray activity and rotation in M dwarfs and predicted time-evolution of the X-ray luminosity

E. Magaudda, B. Stelzer, K. R. Covey, St. Raetz, S. P. Matt, A. Scholz

备注：: Accepted for publication by A&A
DOI：: 10.1051/0004-6361/201937408

摘要：

我们提出了一个样本的14 M矮星观察XMM-牛顿和钱德拉，我们还计算了旋转周期开普勒两轮（K2）任务光变曲线。我们从文献中收集了X射线和旋转数据，并对所有数据集进行了均匀化处理，以提供迄今为止用于X射线活动和旋转研究的最大均匀M矮星样本（302颗恒星）。然后，我们拟合之间的关系$L_{\rm x} - P_{\rm rot}$使用三个不同的质量箱，以分离部分和完全对流星。我们发现一个陡峭的斜率在不饱和制度的完全对流的恒星和非恒定的$L_{\rm x}$水平在饱和制度的所有群众。在$L_{\rm x}/L_{\rm bol}-R_{\rm O}$空间中，我们发现了一个显著的双能隙，它可能与不连续的周期演化有关。然后，我们结合角动量演化模型预测的$P_{\rm rot}$的演化与我们的经验$L_{\rm x} - P_{\rm rot}$关系的新结果，提供了一个估计的年龄衰减的X射线光度。我们将这种关系的预测与已知年龄从1亿年到几十亿年的M星的实际X射线光度进行比较。我们发现预测的$L_{\rm x}$和部分对流星的观测值之间非常好的协议。然而，对于几十亿年的完全对流恒星，由于角动量演化模型低估了这些恒星的自转周期，因此构建的$L_{\rm x}-$年龄关系高估了X射线光度。最后，我们研究了不同参数化的Rossby数（$R_{\rm O}$）的活性旋转关系的形状在$L_{\rm x}/L_{\rm bol}-R_{\rm O}$空间的效果，我们发现，在不饱和制度的斜率和双幂律的断点的位置依赖于敏感的选择$R_{\rm O}$。

英文摘要：

We present a sample of 14 M dwarf stars observed with XMM-Newton and Chandra, for which we also computed rotational periods from Kepler Two-Wheel (K2) Mission light curves. We compiled X-ray and rotation data from the literature and homogenized all data sets to provide the largest uniform sample of M dwarfs (302 stars) for X-ray activity and rotation studies to date. We then fit the relation between $L_{\rm x} - P_{\rm rot}$ using three different mass bins to separate partially and fully convective stars. We found a steeper slope in the unsaturated regime for fully convective stars and a nonconstant $L_{\rm x}$ level in the saturated regime for all masses. In the $L_{\rm x}/L_{\rm bol}-R_{\rm O}$ space we discovered a remarkable double gap that might be related to a discontinuous period evolution. Then we combined the evolution of $P_{\rm rot}$ predicted by angular momentum evolution models with our new results on the empirical $L_{\rm x} - P_{\rm rot}$ relation to provide an estimate for the age decay of X-ray luminosity. We compare predictions of this relationship with the actual X-ray luminosities of M stars with known ages from 100 Myr to a few billion years. We find remarkably good agreement between the predicted $L_{\rm x}$ and the observed values for partially convective stars. However, for fully convective stars at ages of a few billion years, the constructed $L_{\rm x}-$age relation overpredicts the X-ray luminosity because the angular momentum evolution model underpredicts the rotation period of these stars. Finally, we examine the effect of different parameterizations for the Rossby number ($R_{\rm O}$) on the shape of the activity-rotation relation in $L_{\rm x}/L_{\rm bol}-R_{\rm O}$ space, and we find that the slope in the unsaturated regime and the location of the break point of the dual power-law depend sensitively on the choice of $R_{\rm O}$.

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