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arXiv 1802.01031astro-ph.SR
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冷、活跃、短周期双星系统$σ^2$ Coronae Borealis的磁场拓扑

Magnetic field topology of the cool, active, short-period binary system $σ^2$ Coronae Borealis

L. Rosén, O. Kochukhov, E. Alecian, C. Neiner, J. Morin, G. A. Wade, the BinaMIcS collaboration

备注：
12 pages, 9 figures; accepted for publication in A&A
发表信息：
A&A 613, A60 (2018)
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摘要：

这项工作的目标是研究冷，活跃的双星$σ^2$ CrB，重点是它的磁场。我们使用了TBL的Narval和CFHT的ESPaDOns双分光偏振计的斯托克斯$IV$数据。采用最小二乘多线反褶积技术提高了资料的信噪比。然后，我们采用了一种新的二进制塞曼多普勒成像代码，同时重建两个组件的磁拓扑结构和亮度分布。这项分析是在2014年和2017年的两个观测时期进行的。一个先前未经证实的主星磁场已经被安全地探测到。次级的极化特征似乎具有比初级更大的系统振幅。这对应于更强的磁场，对于该磁场，次级的磁能超过初级的磁能3.3-5.7倍。虽然在这两个时期，次级恒星的磁能是相似的，但在2017年，初级恒星的磁能大约是两倍。这两颗恒星在较早纪元（2014年）的磁场拓扑结构非常不同。在较早的时期，在可见极的磁场似乎是相反的极性为初级和次级，这表明连接磁层。这两个$σ^2$ CrB组件的视旋转周期长于轨道周期，我们解释为一个类似太阳的差异旋转的证据。尽管它们的基本参数几乎相同，$σ^2$ CrB系统的组件表现出不同的磁场特性。这表明磁发电机过程是恒星参数的一个非常敏感的函数。

英文摘要：

The goal of this work is to study the cool, active binary star $σ^2$ CrB, focussing on its magnetic field. We used Stokes $IV$ data from the twin spectropolarimeters Narval at the TBL and ESPaDOnS at the CFHT. The least-squares deconvolution multi-line technique was used to increase the signal-to-noise ratio of the data. We then applied a new binary Zeeman-Doppler imaging code to reconstruct simultaneously the magnetic topology and brightness distribution of both components. This analysis was carried out for two observational epochs in 2014 and 2017. A previously unconfirmed magnetic field of the primary star has been securely detected. The polarisation signatures of the secondary appear to have a systematically larger amplitude than that of the primary. This corresponds to a stronger magnetic field, for which the magnetic energy of the secondary exceeds that of the primary by a factor of 3.3-5.7. While the magnetic energy is similar for the secondary star in the two epochs, the magnetic energy is about twice as high in 2017 for the primary. The magnetic field topology of the two stars in the earlier epoch (2014) is very different. In the earlier epoch, the magnetic field at the visible pole appears to be of opposite polarity for the primary and secondary, suggesting linked magnetospheres. The apparent rotational periods of both $σ^2$ CrB components are longer than the orbital period, which we interpret as an evidence of a solar-like differential rotation. Despite their nearly identical fundamental parameters, the components of $σ^2$ CrB system exhibit different magnetic field properties. This indicates that the magnetic dynamo process is a very sensitive function of stellar parameters.

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