M-dwarf stars are well known for the intense magnetic activity that many of them exhibit. In cool stars with near-surface convection zones, this magnetic activity is thought to be driven largely by the interplay of convection and the large scale differential rotation and circulations it establishes. The highly nonlinear nature of these flows yields a fascinatingly sensitive and diverse parameter space, with a wide range of possible dynamics. We report here on a set of three global MHD simulations of rapidly rotating M2 (0.4 $M_\odot$) stars. Each of these three models established nests of vigorous convection that were highly modulated in longitude at low latitudes. Slight differences in their magnetic parameters led each model to disparate dynamo states, but the effect of the convective nest was a unifying feature. In each case, the action of longitudinally modulated convection led to localized (and in one case, global) reversals of the toroidal magnetic field, as well as the formation of an active longitude, with enhanced poloidal field amplitudes and flux emergence.
The Changing Face of $α$ Centauri B: Probing plage and stellar activity in K-dwarfs
恒星活动的详细知识对于理解恒星发电机至关重要，并且将系外行星径向速度检测极限推向地球模拟确认。我们直接比较档案HARPS光谱在$α$ Cen B的活动周期的最小值时，一个高活性状态时，清晰的旋转调制的$\log{R'_{HK}}$是可见的。相对于非活性光谱，我们发现了大量的窄赝发射功能的强度旋转调制的活性光谱。这些特征最有可能来源于斑、斑点或两者的组合。它们还显示$\sim$ 300 m s $^{-1}$的径向速度变化-与恒星表面旋转的活动区域一致。此外，我们看到的证据表明，一些线起源于“活跃的完美”光球出现更广泛的相对于“不活跃的完美”的情况。这可能是由于例如磁亮点对这些线的贡献增强，这然后导致额外的线加宽。更详细的分析可能使未来使用单光谱测量谱斑和斑点覆盖率成为可能。
High-Resolution Modelling of Coronae and Winds in Solar-type Stars with Varying Rotation Rates I. X-ray Coronae
Nanjing University（南京大学）；Leibniz Institute for Astrophysics Potsdam（波茨坦阿基米德研究所）；SETI Institute（SETI研究所）；University of Potsdam, Institute of Physics and Astronomy（波茨坦大学物理与天文研究所）；Kyoto University（京都大学）；Aalto University（阿尔托大学）；Max-Planck-Institut für Sonnensystemforschung（马克斯·普朗克太阳系统研究所）；Nordita, KTH Royal Institute of Technology & Stockholm University（北欧理论天体物理学中心，瑞典皇家理工学院与斯德哥尔摩大学）
