The magnetic fields, activity and dynamos of young solar-type stars can be empirically studied using time-series of spectropolarimetric observations and tomographic imaging techniques such as Doppler imaging and Zeeman Doppler imaging. In this paper we use these techniques to study the young Sun-like star EK Draconis (Sp-Type: G1.5V, HD 129333) using ESPaDOnS at the Canada-France-Hawaii Telescope and NARVAL at the Tèlescope Bernard Lyot. This multi-epoch study runs from late 2006 until early 2012. We measure high levels of chromospheric activity indicating an active, and varying, chromosphere. Surface brightness features were constructed for all available epochs. The 2006/7 and 2008 data show large spot features appearing at intermediate-latitudes. However, the 2012 data indicate a distinctive polar spot. We observe a strong, almost unipolar, azimuthal field during all epochs that is similar to that observed on other Sun-like stars. Using magnetic features, we determined an average equatorial rotational velocity, Ω_eq, of 2.50 +/- 0.08 rad/d. High levels of surface differential rotation were measured with an average rotational shear, ΔΩ, of 0.27 +0.24-0.26 rad/d. During an intensively observed 3-month period from December 2006 until February 2007, the magnetic field went from predominantly toroidal ( approx. 80%) to a more balanced poloidal-toroidal (approx. 40-60%) field. Although the large-scale magnetic field evolved over the epochs of our observations, no polarity reversals were found in our data.
Magnetic activity on the young Sun: a case study of EK Draconis
Konkoly Observatory, HUN-REN Research Centre for Astronomy and Earth Sciences（孔科利天文台，HUN-REN 地球与天文学科学研究中心）；HUN-REN CSFK, MTA Centre of Excellence（HUN-REN CSFK，MTA 卓越中心）；Eötvös Loránd University, Institute of Physics and Astronomy, Department of Astronomy（厄特沃什·罗兰大学，物理与天文学研究所，天文学系）
Multiwavelength Campaign Observations of a Young Solar-type Star, EK Draconis. II. Understanding Prominence Eruption through Data-Driven Modeling and Observed Magnetic Environment
Time evolution of magnetic activity cycles in young suns: The curious case of kappa Ceti
对年轻的类太阳恒星的磁特性进行详细的研究，可以为我们的太阳的磁过去及其对早期地球的影响提供有价值的信息。我们使用50年的色球活动数据和6个时期的分光偏振观测，确定适度旋转的年轻类太阳恒星Kappa Ceti的磁性和活动周期的属性。通过测量Ca II H和K线的通量来确定色球活动。一个广义的Lomb-Scargle周期图和小波分解的色球活动数据，以建立相关的周期性。利用塞曼多普勒成像技术对该恒星的偏振分光观测数据进行了矢量磁场重建。我们的周期分析算法检测到一个3.1年的色球周期，除了恒星的著名的6年周期。虽然这两个循环周期的比例约为1：2，但它们表现出不寻常的时间演变。此外，分光偏振数据分析显示了恒星大尺度磁场的极性反转，这表明了一个大约10年的磁场或海尔周期。这颗恒星色球周期的不寻常演化，以及它们与磁周期的缺乏直接相关性，使鲸鱼座κ成为一颗好奇的年轻太阳。这种复杂的磁场活动演化可能与适度活跃的年轻太阳同义，这是我们自己的太阳可能采取的演化路径。
Time-Resolved Connection between Starspots and Flares in Nearby Young Solar-type Stars Observed by TESS
Kyoto University（京都大学）；NASA Goddard Space Flight Center（美国国家航空航天局戈达德太空飞行中心）；The Catholic University of America（美利坚天主教大学）；The Hakubi Center for Advanced Research, Kyoto University（京都大学Hakubi高级研究中心）
Dynamo cycles in global convection simulations of solar-like stars
几颗类太阳恒星表现出类似于太阳的周期性磁场活动，如在光球和色球层发射中发现的。我们希望了解这些活动周期的旋转依赖性所涉及的物理机制。我们使用三维磁流体动力学模拟的全球对流发电机模型的类太阳恒星的发电机的旋转依赖性进行调查。我们进一步应用测试场方法来确定这些模拟中的$α$效应。我们发现发电机具有明确的振荡平均磁场为中度和快速旋转运行。对于较慢的旋转，场是恒定的或呈现不规则的周期。在中等和快速旋转区，循环周期随旋转而微弱增加。这种行为可以很好地解释与帕克-吉村发电机波赤道旅行。尽管$α$效应随着旋转的增加而变得更强，但剪切减小得更陡，导致这种对旋转的弱依赖性。与其他数值研究类似，我们没有发现Brandenburg等人（1998）提出的活动分支。然而，我们的模拟似乎更符合Distefano et al.（2017）和Olspert et al.（2017）提出的过渡分支。如果太阳表现出类似于我们在模拟中发现的发电机波，它将在对流区深处运行。
Algebraic Quantification of the Contribution of Active Regions to the Sun's Dipole Moment: Applications to Century-scale Polar Field Estimates and Solar Cycle Forecasting
Summary of the First Year of the Space Weather Around Young Suns Program: 900 Hours of Low-frequency Radio and Optical Data Dedicated to Young, Solar-type Stars
Cahill Center for Astronomy and Astrophysics, California Institute of Technology（加州理工学院卡希尔天文与天体物理中心）；Owens Valley Radio Observatory, California Institute of Technology（加州理工学院欧文斯谷射电天文台）；ASTRON, Netherlands Institute for Radio Astronomy（荷兰射电天文研究所 ASTRON）；Jet Propulsion Laboratory, California Institute of Technology（加州理工学院喷气推进实验室）；Caltech Optical Observatories, California Institute of Technology（加州理工学院光学天文台）；School of Earth and Space Exploration, Arizona State University（亚利桑那州立大学地球与空间探索学院）
Disambiguation of Vector Magnetograms by Stereoscopic Observations from the Solar Orbiter/Polarimetric and Helioseismic Imager (PHI) and the Solar Dynamic Observatory (SDO)/Helioseismic and Magnetic Imager (HMI)
