极性相反的温暖和寒冷的恒星黑子。用PEPSI对飞马座II的高分辨率塞曼多普勒成像研究
Warm and cool starspots with opposite polarities. A high-resolution Zeeman-Doppler-Imaging study of II Pegasi with PEPSI
摘要：
我们提出了一个温度和磁场的表面地图的K2次巨星的活动二世钉。采用的是高分辨率斯托克斯IV光谱获得的新波茨坦Echelle偏振和光谱仪（PEPSI）在大双目望远镜（LBT）。我们的主要结果是，II Peg上的温度特征与其磁场拓扑结构密切相关。我们发现一个正极性的暖点（相对于有效温度温暖350 K）和径向场密度为1.1kG的冷点（780 K冷却器）共存的负极性的2kG。其他几个很酷的功能重建包含两个极性和（径向）场密度高达2千克。最大的冷点重建的温度对比度为550 K，几乎10%的可见半球的面积，并与多极磁形态。在两个表面区域中检测到高达+/-500G的场的角向分量和方位分量，这两个表面区域在具有强径向场但不同极性的斑点之间。一个无力的磁场外推表明，不同的极性的冷点和积极的极性的暖点是物理相关的，通过一个系统的日冕环的典型高度约。2颗R星。虽然H-α线核心和它的红边翼在所有旋转阶段都表现出变化，但当暖点接近恒星中央子午线时，H-α发射的蓝移主要增加，表明其环路内的高速质量运动。我们解释了温暖的斑点，由于光球加热的冲击波前从不同极性的区域之间的虹吸式流动，而大多数的冷点可能是由于预期的对流抑制，如在太阳上形成。
英文摘要：
We present a temperature and a magnetic-field surface map of the K2 subgiant of the active binary II Peg. Employed are high resolution Stokes IV spectra obtained with the new Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT). Our main result is that the temperature features on II Peg closely correlate with its magnetic field topology. We find a warm spot (350K warmer with respect to the effective temperature) of positive polarity and radial field density of 1.1 kG coexisting with a cool spot (780K cooler) of negative polarity of 2 kG. Several other cool features are reconstructed containing both polarities and with (radial) field densities of up to 2 kG. The largest cool spot is reconstructed with a temperature contrast of 550 K, an area of almost 10% of the visible hemisphere, and with a multipolar magnetic morphology. A meridional and an azimuthal component of the field of up to +/-500G is detected in two surface regions between spots with strong radial fields but different polarities. A force-free magnetic-field extrapolation suggests that the different polarities of cool spots and the positive polarity of warm spots are physically related through a system of coronal loops of typical height of approx. 2 Rstar. While the H-alpha line core and its red-side wing exhibit variations throughout all rotational phases, a major increase of blue-shifted H-alpha emission was seen for the phases when the warm spot is approaching the stellar central meridian indicating high-velocity mass motion within its loop. We explain the warm spots due to photospheric heating by a shock front from a siphon-type flow between regions of different polarities while the majority of the cool spots is likely formed due to the expected convective suppression like on the Sun.
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