EK波江座：从磁性Ap星演化而来的巨星的冰山一角
EK Eridani: the tip of the iceberg of giants which have evolved from magnetic Ap stars
摘要：
我们观测缓慢旋转的活动单巨星EKEri，直接研究和推断其磁场的性质。我们使用伯纳德·李奥望远镜的分光偏振计NARVAL，南峰天文台，和最小二乘反卷积方法来创建高信噪比斯托克斯V轮廓。我们用大尺度磁场模型拟合了斯托克斯V型分布。我们研究了经典的活性指示剂，CaII的H和K线，CaII的红外三线态，和Hα线。我们安全地探测到了EK Eri的斯托克斯V信号，并测量了跨越60%旋转周期的七个单独日期的纵向磁场BI。测得的Ek Eri的纵向磁场达到约100 G，与在RSCVn或FK Com型恒星中观察到的磁场一样强：这与在缓慢旋转的MS恒星或任何先前用NARVAL观察到的单个红巨星表面观察到的弱磁场相比，是非常不寻常的。从我们的模型，我们推断，平均表面磁场约为270 G，和大规模的磁场是由极向分量占主导地位。这与对强磁性Ap星的后代的期望是一致的。
英文摘要：
We observe the slowly-rotating, active, single giant, EK Eri, to study and infer the nature of its magnetic field directly. We used the spectropolarimeter NARVAL at the Telescope Bernard Lyot, Pic du Midi Observatory, and the Least Square Deconvolution method to create high signal-to-noise ratio Stokes V profiles. We fitted the Stokes V profiles with a model of the large-scale magnetic field. We studied the classical activity indicators, the CaII H and K lines, the CaII infrared triplet, and Hαline. We detected the Stokes V signal of EK Eri securely and measured the longitudinal magnetic field Bl for seven individual dates spanning 60% of the rotational period. The measured longitudinal magnetic field of EK Eri reached about 100 G and was as strong as fields observed in RSCVn or FK Com type stars: this was found to be extraordinary when compared with the weak fields observed at the surfaces of slowly-rotating MS stars or any single red giant previously observed with NARVAL. From our modeling, we infer that the mean surface magnetic field is about 270 G, and that the large scale magnetic field is dominated by a poloidal component. This is compatible with expectations for the descendant of a strongly magnetic Ap star.
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