We report the detailed history of spin-period changes in five intermediate polars (DQ Herculis, AO Piscium, FO Aquarii, V1223 Sagittarii, and BG Canis Minoris) during the 30-60 years since their original discovery. Most are slowly spinning up, although there are sometimes years-long episodes of spin-down. This is supportive of the idea that the underlying magnetic white dwarfs are near spin equilibrium. In addition to the ~40 stars sharing many properties and defined by their strong, pulsed X-ray emission, there are a few rotating much faster (P<80 s), whose membership in the class is still in doubt -- and who are overdue for closer study.

中文翻译：

---

中间极地的自旋周期历史

我们报告了五个中间极地（DQ Herculis、AO Piscium、FO Aquarii、V1223 Sagittarii 和 BG Canis Minoris）自最初发现以来的 30-60 年自旋周期变化的详细历史。大多数都在缓慢旋转，尽管有时会出现长达数年的减速期。这支持了下面的磁性白矮星接近自旋平衡的想法。除了大约 40 颗共享许多特性并由其强烈的脉冲 X 射线发射定义的恒星之外，还有一些旋转得更快（P <80 s），其在该类中的成员资格仍然存在疑问——并且谁是逾期进行更深入的研究。