标题： 通过K2任务、X射线和紫外数据理解M型矮星的旋转-活动关系的路径 显示英文标题

标题： A path towards understanding the rotation-activity relation of M dwarfs with K2 mission, X-ray and UV data

摘要： 我们研究了134颗明亮的邻近M型矮星在开普勒双轮（K2）任务期间的C0到C4阶段观测中恒星自转与磁活动之间的关系。 K2光变曲线为97颗恒星（其中79颗之前没有周期测量）提供了光度学推导的自转周期，以及与冷斑和耀斑相关的各种活动指标。 我们发现快自转星和慢自转星之间存在明显差异，分界线在约10天的周期处，此时活动水平突然变化。 所有光度学活动诊断（斑点周期振幅、耀斑峰值振幅以及减去斑点和耀斑变化后的剩余变化）都显示出相同的二分法，表明快自转星的高活动模式和慢自转星的低活动模式之间存在快速过渡。 这种未被解释的行为让人联想到数值模拟中看到的动力学模式变化，该变化将偶极子模式与多极子模式分开。 相当数量的快自转星是目视双星。 一种初步的解释是双星中盘演化加速，导致主序星上更高的初始自转速率以及相关的更长的自转减速和活动寿命。 我们将K2的自转周期与档案中的X射线和紫外数据相结合。 分别在我们的样本中发现了26、41和11颗恒星的X射线、远紫外（FUV）和近紫外（NUV）检测。 将快自转星与慢自转星分开，我们首次分别确定了早M星和中M星的X射线饱和水平。 显示英文摘要

摘要： We study the relation between stellar rotation and magnetic activity for a sample of 134 bright, nearby M dwarfs observed in the Kepler Two-Wheel (K2) mission during campaigns C0 to C4. The K2 lightcurves yield photometrically derived rotation periods for 97 stars (79 of which without previous period measurement), as well as various measures for activity related to cool spots and flares. We find a clear difference between fast and slow rotators with a dividing line at a period of ~10d at which the activity level changes abruptly. All photometric diagnostics of activity (spot cycle amplitude, flare peak amplitude and residual variability after subtraction of spot and flare variations) display the same dichotomy, pointing to a quick transition between a high-activity mode for fast rotators and a low-activity mode for slow rotators. This unexplained behavior is reminiscent of a dynamo mode-change seen in numerical simulations that separates a dipolar from a multipolar regime. A substantial number of the fast rotators are visual binaries. A tentative explanation is accelerated disk evolution in binaries leading to higher initial rotation rates on the main-sequence and associated longer spin-down and activity lifetimes. We combine the K2 rotation periods with archival X-ray and UV data. X-ray, FUV and NUV detections are found for 26, 41, and 11 stars from our sample, respectively. Separating the fast from the slow rotators, we determine for the first time the X-ray saturation level separately for early- and for mid-M stars.