Variable magnetic field geometry of the young sun HN Pegasi (HD 206860)
Variable magnetic field geometry of the young sun HN Pegasi (HD 206860)
复制标题
年轻太阳 HN Pegasi (HD 206860) 的可变磁场几何结构
DOI：
10.1051/0004-6361/201424096
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发表时间：
2015
影响因子：
6.5
通讯作者：
Jeffers
中科院分区：
文献类型：
--
作者：
Boro Saikia;Jeffers
从太阳型恒星的偏振光谱观测中重建的大尺度磁场为了解其潜在的动力过程提供了重要的见解。我们的目的是研究一个年轻的太阳类似物G0矮星HN Peg的大尺度表面磁场和色球活动的时间变化。方法利用塞曼多普勒成像技术，在7年6个观测期重建大尺度地表磁场拓扑结构。我们还通过测量三种色球活性指标（Ca II HK、Hα和Ca II IRT）线核的通量来研究色球活性的变化。结果HN - Peg的磁性拓扑结构具有复杂多变的几何结构。在每个观测年代，径向磁场在两极呈现稳定的正极性磁场区，而方位角磁场的强度变化很大，在赤道纬度存在一个强的正极性磁场带。这个场在我们的时间跨度的中间消失，在最后两个观测时期再次出现。从磁图中得到的平均磁场也遵循与环面磁场相似的趋势，磁场强度在2009.54历元达到最小值。将每次观测的可见表面上的视线磁场相加，HN Peg显示出弱的纵向磁场（Bl），范围为- 14 G至13 G，尽管在每个历元内存在显著的旋转变化，但没有明显的长期趋势。这些色球活动指标在观测的时间跨度中表现出更长期的变化，其中最小的观测是在Epoch 2008.71。
ContextThe large-scale magnetic field of solar-type stars reconstructed from their spectropolarimetric observations provide important insight into their underlying dynamo processes.AimsWe aim to investigate the temporal variability of the large-scale surface magnetic field and chromospheric activity of a young solar analogue, the G0 dwarf HN Peg.MethodsThe large-scale surface magnetic field topology is reconstructed using Zeeman Doppler imaging at six observational epochs covering seven years. We also investigated the chromospheric activity variations by measuring the flux in the line cores of the three chromospheric activity indicators: Ca II HK, Hα, and the Ca II IRT lines.ResultsThe magnetic topology of HN Peg shows a complex and variable geometry. While the radial field exhibits a stable positive polarity magnetic region at the poles at each observational epoch, the azimuthal field is strongly variable in strength, where a strong band of positive polarity magnetic field is present at equatorial latitudes. This field disappears during the middle of our timespan, reappearing again during the last two epochs of observations. The mean magnetic field derived from the magnetic maps also follow a similar trend to the toroidal field, with the field strength at a minimum in epoch 2009.54. Summing the line of sight magnetic field over the visible surface at each observation, HN Peg exhibits a weak longitudinal magnetic field (Bl) ranging from −14 G to 13 G, with no significant long-term trend, although there is significant rotational variability within each epoch. Those chromospheric activity indicators exhibit more long-term variations over the time span of observations, where the minimal is observed in Epoch 2008.71.