论文标题
强烈磁性迅速振荡AP星HD 166473的10.5年旋转周期
The 10.5 year rotation period of the strongly magnetic rapidly oscillating Ap star HD 166473
论文作者
论文摘要
磁场如何有助于AP恒星的旋转速率的差异，并影响其中某些旋转速率的发生是重要的开放问题。通过研究其中一些最极端的示例，可以从这些问题中获得宝贵的见解。超慢旋转的迅速振荡AP（ROAP）星HD 166473就是一个例子。我们根据1992年至2019年之间在各种观测值和各种仪器配置之间获得的高分辨率光谱对56个平均磁场模量<b>的56测量的分析进行了第一个精确测定（3836 +/- 30）d。我们考虑了一组不均匀的纵向磁场<b_z>跨越相同时间间隔的21个确定的不均匀组。这使得HD 166473成为仅有超过10年时间的四个AP恒星之一，而该恒星超过了10年，而磁场测量已超过整个周期。余弦波很好地近似<b>和<b_z>的变化曲线。 HD 166473的磁场似乎仅偏离轴对称性，但肯定涉及相当大的非偶极成分。在具有全相覆盖的磁场测量值的旋转周期超过1000 d的恒星中，HD 166473具有最强的场。它的磁场也是ROAP恒星中最强的磁场之一。总体而言，HD 166473的磁性似乎与更快的旋转AP星的磁性不同。然而，考虑到一组精确确定的周期长于1000 d并且其磁变化在整个周期中的表征的八个AP恒星表明其磁性和旋转轴之间的角度往往是系统上大的。
How magnetic fields contribute to the differentiation of the rotation rates of the Ap stars and affect the occurrence of non-radial pulsation in some of them are important open questions. Valuable insight can be gained into these questions by studying some of the most extreme examples of the processes at play. The super-slowly rotating rapidly oscillating Ap (roAp) star HD 166473 is such an example. We performed the first accurate determination of its rotation period, (3836 +/- 30)d, from the analysis of 56 measurements of the mean magnetic field modulus <B> based on high-resolution spectra acquired between 1992 and 2019 at various observatories and with various instrumental configurations. We complemented this analysis with the consideration of an inhomogeneous set of 21 determinations of the mean longitudinal magnetic field <B_z> spanning the same time interval. This makes HD 166473 one of only four Ap stars with a period longer than 10 years for which magnetic field measurements have been obtained over more than a full cycle. The variation curves of <B> and of <B_z> are well approximated by cosine waves. The magnetic field of HD 166473 only seems to deviate slightly from axisymmetry, but it definitely involves a considerable non-dipolar component. Among the stars with rotation periods longer than 1000 d for which magnetic field measurements with full phase coverage are available, HD 166473 has the strongest field. Its magnetic field is also one of the strongest known among roAp stars. Overall, the magnetic properties of HD 166473 do not seem fundamentally distinct from those of the faster-rotating Ap stars. However, considering as a group the eight Ap stars that have accuractely determined periods longer than 1000 d and whose magnetic variations have been characterised over a full cycle suggests that the angles between their magnetic and rotation axes tend to be systematically large.
