本文通过 TESS 候选体的高分辨率光谱观测确认了 17 颗超慢自转 Ap 星，新测得一批磁场数据并发现多个分光双星，验证了搜寻方法并支持了 Ap 星磁场强度与自转周期关系的初步结论。
摘要：
为了更好地理解自转周期最长的 Ap 星，我们获取了一批由 TESS 测光巡天识别出的超慢自转 Ap（ssrAp）星候选体的高分辨率光谱，以确认它们确为 Ap 星，检验其 v sin i 值是否与超慢自转相符，并首次估计它们的磁场强度。我们尽可能确定了它们的平均磁场模量、平均二次磁场以及投影赤道速度的上限。在所研究的 27 颗恒星中，有 18 颗是典型的 Ap 星；其余 9 颗中的大多数似乎被错误分类。其中一颗 Ap 星并非慢自转体；它必定几乎以极向视角被观测到。其余 17 颗的性质与中等至极端长的自转周期相符。我们新发现了 8 颗在可见光波段具有可分辨磁分裂线的恒星，并测量了它们的平均磁场模量和平均二次磁场；另有 5 颗恒星也测得了平均二次磁场。我们还识别出 5 个包含 Ap 星的新分光双星系统。在被错误分类的恒星中，还发现了一个由两颗相似、谱线锐利的 Am 型子星组成的 SB2 系统。我们利用 TESS 数据搜寻 ssrAp 星候选体的技术得到了验证，但似乎受到 Ap 星光谱分类不确定性的限制。本研究获得的新磁场测量结果进一步支持了我们此前研究的初步结论：在磁场强于约 7.5 kG 的恒星中不存在长于约 150 天的周期；磁场强度低于约 2 kG 时超慢自转的出现率低于约 3-7.5 kG 范围；以及磁场强度在约 2 至 3 kG 之间的慢自转 Ap 星存在缺失。
英文摘要：
To gain better understanding of the Ap stars with the longest rotation periods, we obtained high resolution spectra of a sample of super-slowly rotating Ap (ssrAp) star candidates identified by a TESS photometric survey, to confirm that they are indeed Ap stars, to check that their v sin i values are compatible with super-slow rotation, and to obtain a first estimate of their magnetic field strengths. We determined whenever possible their mean magnetic field modulus, their mean quadratic magnetic field, and an upper limit of their projected equatorial velocities. Eighteen of the 27 stars studied are typical Ap stars; most of the other nine appear to be misclassified. One of the Ap stars is not a slow rotator; it must be seen nearly pole-on. The properties of the remaining 17 are compatible with moderately to extremely long rotation periods. Eight new stars with resolved magnetically split lines in the visible range were discovered; their mean magnetic field modulus and their mean quadratic magnetic field were measured. The mean quadratic field could also be determined in five more stars. Five new spectroscopic binaries containing an Ap star were identified. Among the misclassified stars, one SB2 system with two similar, sharp-lined Am components was also discovered. The technique that we used to carry out a search for ssrAp star candidates using TESS data is validated, but appears limited by uncertainties in the spectral classification of Ap stars. The new magnetic field measurements obtained as part of this study lend further support to the tentative conclusions of our previous studies: the absence of periods longer than ~150 d in stars with magnetic fields stronger than ~7.5 kG, the lower rate of occurrence of super-slow rotation for field strengths less than ~2 kG than in the range ~3-7.5 kG, and the deficiency of slowly rotating Ap stars with field strengths between ~2 and ~3 kG.
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The transport of angular momentum for massive stars I. Formation of slowly rotating WNE stars
Yunnan Observatories, Chinese Academy of Sciences（中国科学院云南天文台）；University of Chinese Academy of Sciences（中国科学院大学）；Key Laboratory for Structure and Evolution of Celestial Objects, Chinese Academy of Sciences（中国科学院天体结构与演化重点实验室）；International Centre of Supernovae, Yunnan Key Laboratory（国际超新星中心云南省重点实验室）；Center for Astronomical Mega-Science, Chinese Academy of Sciences（中国科学院天文大科学研究中心）
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