前主序星双星系统HD 155555的第一张磁图
The first magnetic maps of a pre-main sequence binary star system - HD 155555
摘要：
本文首次给出了一个前主序星双星系统的表面磁场图。2004年和2007年，英澳望远镜获得了年轻的1800万年前HD 155555（V824 Ara，G5 IV + K 0 IV）系统的分光偏振观测。这两个数据集进行了分析，使用一个新的二进制塞曼多普勒成像（ZDI）代码。这使我们能够同时模拟每个组分对所观察到的圆偏振光谱的贡献。恒星亮度地图也产生了HD 155555和以前的多普勒图像相比。我们的径向磁图揭示了一个复杂的表面磁拓扑结构与混合极性在所有纬度。我们发现两颗恒星的方位场环，其中大部分被发现是非轴对称的恒星旋转轴。我们还研究了磁场强度和相对分数的磁能存储在径向和方位角的字段组件在这两个时代。在2004年和2007年之间，观测到二级恒星的磁场强度明显减弱。这是伴随着一个明显的移位的位置的磁能从方位角的径向场。我们认为，这可能是一个磁活动周期的指示。我们使用径向磁场图来外推每颗恒星的日冕场（通过假设一个势场）-目前忽略任何可能的相互作用。在这两个历元中，次级恒星的大尺度磁场都与其自转轴呈极端倾斜（~75度）。场的复杂性，这是明显的表面映射持续到一个显着的分数的二进制分离。因此，两颗恒星的场之间的任何相互作用也可能是复杂的。对此进行建模将需要完整的二元场外推。
英文摘要：
We present the first maps of the surface magnetic fields of a pre-main sequence binary system. Spectropolarimetric observations of the young, 18 Myr, HD 155555 (V824 Ara, G5IV + K0IV) system were obtained at the Anglo-Australian Telescope in 2004 and 2007. Both datasets are analysed using a new binary Zeeman Doppler imaging (ZDI) code. This allows us to simultaneously model the contribution of each component to the observed circularly polarised spectra. Stellar brightness maps are also produced for HD 155555 and compared to previous Doppler images. Our radial magnetic maps reveal a complex surface magnetic topology with mixed polarities at all latitudes. We find rings of azimuthal field on both stars, most of which are found to be non-axisymmetric with the stellar rotational axis. We also examine the field strength and the relative fraction of magnetic energy stored in the radial and azimuthal field components at both epochs. A marked weakening of the field strength of the secondary star is observed between the 2004 and 2007 epochs. This is accompanied by an apparent shift in the location of magnetic energy from the azimuthal to radial field. We suggest that this could be indicative of a magnetic activity cycle. We use the radial magnetic maps to extrapolate the coronal field (by assuming a potential field) for each star individually - at present ignoring any possible interaction. The secondary star is found to exhibit an extreme tilt (~75 deg) of its large scale magnetic field to that of its rotation axis for both epochs. The field complexity that is apparent in the surface maps persists out to a significant fraction of the binary separation. Any interaction between the fields of the two stars is therefore likely to be complex also. Modelling this would require a full binary field extrapolation.
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