中间极MU Cam的广泛测光：自旋周期变化的探测
Extensive photometry of the intermediate polar MU Cam: detection of a spin period change
摘要：
具有已知自旋周期变化率的中间极并不多，因为这样的任务需要长时间进行测量。为了测量自旋周期变化，MU Cam是一个很好的候选者，因为它具有大幅度的自旋振荡，能够实现高精度的测量。幸运的是，在过去的旋转周期的MU凸轮测量精度很高。为了重新测量旋转周期，在2014-2015年，我们对MU Cam进行了广泛的光度观测，在46个夜晚内总共持续了208小时。我们发现自旋、边带和轨道周期分别等于1187.16245+/-0.00047 s、1276.3424+/-0.0022 s和4.71942+/-0.00016 h。将测量的自旋周期与过去MU Cam的自旋周期进行比较，我们检测到自旋周期变化为dP/dt=-（2.17+/-0.10）X 10^（-10）。自转周期的变化率并不稳定，而且在几年的时间尺度内变化。在2014年4月至5月的四个晚上，MU Cam比平时暗了0.8等，边带振荡的幅度是平时的五倍，这表明盘溢出吸积的比例很大。在正常亮度状态下，边带振荡呈现双峰脉冲波形。当恒星亮度降低0.8等时，边带振荡呈现单峰脉冲轮廓。相比之下，自旋脉冲，这是准正弦曲线，保持非常稳定的轮廓和幅度。此外，自旋脉冲在几年甚至几十年的时间尺度上也非常稳定。MU凸轮是非常感兴趣的，因为它代表了一个独特的对象与一个大的和不稳定的自旋周期变化率，并表现出独特的行为的脉冲轮廓。
英文摘要：
Intermediate polars with known rates of spin period changes are not numerous because such tasks require measurements performed for a long time. To measure a spin period change, MU Cam is a good candidate because it has a spin oscillation with a large amplitude enabling measurements with high precision. Fortunately, in the past the spin period of MU Cam was measured with high precision. To measure the spin period anew, in 2014-2015 we performed extensive photometric observations of MU Cam, spanning a total duration of 208 h within 46 nights. We found that the spin, sideband and orbital periods are equal to 1187.16245+/-0.00047 s, 1276.3424+/-0.0022 s and 4.71942+/-0.00016 h, respectively. Comparing the measured spin period with the spin period of MU Cam in the past, we detected the spin period change with dP/dt=-(2.17+/-0.10) X 10^(-10). This rate of the spin period change was not stable and varied in a time scale of years. During four nights in 2014 April-May MU Cam was fainter than usual by 0.8 mag, and the amplitude of the sideband oscillation was five times larger, denoting significant fraction of disc-overflow accretion. The sideband oscillation showed a double-peaked pulse profile in the normal brightness state. When the star brightness was decreased by 0.8 mag, the sideband oscillation showed a single-peaked pulse profile. In contrast, the spin pulse, which was quasi-sinusoidal, remained remarkably stable both in profile and in amplitude. Moreover, the spin pulse was also remarkably stable in a time scale of years and even decades. MU Cam is of great interest because it represents a distinctive object with a large and unstable rate of the spin period change and exhibits a distinctive behaviour of the pulse profiles.
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