According to most stellar dynamo theories, differential rotation (DR) plays a crucial role for the generation of toroidal magnetic fields. Numerical models predict surface differential rotation to be anti-solar for rapidly-rotating giant stars, i.e., their surface angular velocity could increase with stellar latitude. However, surface differential rotation has been derived only for a handful of individual giant stars to date.
The spotted surface of the K-giant KU Pegasi is investigated in order to detect its time evolution and quantify surface differential rotation.
We present altogether 11 Doppler images from spectroscopic data collected with the robotic telescope STELLA between 2006--2011. All maps are obtained with the surface reconstruction code iMap. Differential rotation is extracted from these images by detecting systematic (latitude-dependent) spot displacements. We apply a cross-correlation technique to find the best differential rotation law.
The surface of KU Peg shows cool spots at all latitudes and one persistent warm spot at high latitude. A small cool polar spot exists for most but not all of the epochs. Re-identification of spots in at least two consecutive maps is mostly possible only at mid and high latitudes and thus restricts the differential-rotation determination mainly to these latitudes. Our cross-correlation analysis reveals solar-like differential rotation with a surface shear of $α=+0.040\pm0.006$, i.e., approximately five times weaker than on the Sun. We also derive a more accurate and consistent set of stellar parameters for KU Peg including a small Li abundance of ten times less than solar.
Doppler-shifted Signatures in the Chromospheric Line Profiles of II Pegasi
Yunnan Observatories, Chinese Academy of Sciences（中国科学院云南天文台）；Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences（中国科学院天体结构与演化重点实验室）；International Centre of Supernovae, Yunnan Key Laboratory（超新星国际中心，云南省重点实验室）；School of Astronomy and Space Science, University of Chinese Academy of Sciences（中国科学院大学天文与空间科学学院）
Doppler imaging combined with high-cadence photometry. I. Revisiting the surface of a pre-main-sequence flare star
Kyoto University（京都大学）；Ankara University（安卡拉大学）；Max-Planck-Institut für Sonnensystemforschung（马克斯·普朗克太阳系研究所）；Hitotsubashi University（一桥大学）；The Hakubi Center for Advanced Research, Kyoto University（京都大学哈库比高级研究中心）；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）；National Astronomical Observatory of Japan（日本国立天文台）；Nishi-Harima Astronomical Observatory, University of Hyogo（兵库县立西播磨天文台）
Lithium enrichment on the single active K1-giant DI Piscium -- Possible joint origin of differential rotation and Li enrichment
我们研究了快速旋转的富锂活动单K巨星DI Psc的表面斑点活动，以测量表面微分旋转并了解锂富集背后的机制。多普勒成像被应用于恢复的表面温度分布的DI Psc在两个随后的旋转周期中使用单独的映射线Ca I 6439，Fe I 6430，Fe I 6421和Li I 6708。通过后续地图的互相关推导出表面差异旋转。差图的产生，以研究锂富集的均匀性的表面上。这些地图进行了比较与旋转调制的Li I 6708线等效宽度。多普勒图像获得的钙和铁映射线同意，并揭示了强大的极地斑点，以及在低纬度地区的凉爽功能。对连续的地图进行互相关，得到切变系数为-0.083 +-0.021的反日差异自转。平均值和Li图的差异表明锂丰度与活动无关。也有一个显着的旋转调制的Li等效宽度。
Adaptive multi-line fitting for stable line-core intensity and Doppler velocity
Queen’s University Belfast（贝尔法斯特女王大学）；California State University Northridge（北岭加州州立大学）；ASI Italian Space Agency（意大利航天局）；University of Trento（特伦托大学）；University of Rome Tor Vergata（罗马托尔维尔加塔大学）
Discovery of a rapidly evolving global magnetic field in the M-dwarf YZ Cet and constraints on the magnetic field of its planet YZ Cet b
Queen’s University（女王大学）；Royal Military College of Canada（加拿大皇家军事学院）；National Centre for Radio Astrophysics, Tata Institute of Fundamental Research（塔塔基础研究所国家射电天体物理中心）；University of Tartu（塔尔图大学）
研究发现M矮星YZ Cet磁场快速演变，揭示其行星YZ Cet b磁场约束，强调监测恒星磁场变化对理解系外行星磁层的重要性。
