标题： 掩食后公共包层双星的轨道周期变化 显示英文标题

标题： Orbital Period Variations in Eclipsing Post Common Envelope Binaries

摘要： 我们展示了高速ULTRACAM测光观测DE CVn、GK Vir、NN Ser、QS Vir、RR Cae、RX J2130.6+4710、SDSS 0110+1326和SDSS 0303+0054食双星，并利用这些数据来测量精确的掩食中时刻以检测周期变化。 我们发现QS Vir的掩食时间存在约250秒的大偏差，这与Applegate机制预测的结果相差一个量级。 唯一能够驱动这种周期变化的机制是处于高度椭圆轨道上的第三天体。 然而，先前提出的该系统中存在的行星/亚恒星伴星被我们的数据排除。 我们的掩食时间表明，NN Ser中检测到的周期减小现象仍在继续，只有磁制动或第三天体能解释这一变化。 先前提出的NN Ser中存在的行星/亚恒星伴星也被我们的数据排除。 我们的精确掩食时间还改进了DE CVn和GK Vir的星历表。 主食甚的宽度直接与次级星的大小相关，而此星大小的变化可能是Applegate机制或Wilson（星斑）凹陷引起的，这可能会导致O-C曲线的抖动。 我们在几年内测量了NN Ser和GK Vir系统的主食甚宽度，但未发现次级星半径有明确变化。 然而，我们的数据足够精确（dRsec / Rsec < 10^-5），未来可以显示Applegate机制的影响。 我们在两个系统中均未发现Wilson凹陷的证据。 我们还初步发现，次级星的耀发率可能与其质量而非自转速率有关。 显示英文摘要

摘要： We present high speed ULTRACAM photometry of the eclipsing post common envelope binaries DE CVn, GK Vir, NN Ser, QS Vir, RR Cae, RX J2130.6+4710, SDSS 0110+1326 and SDSS 0303+0054 and use these data to measure precise mid-eclipse times in order to detect any period variations. We detect a large (~ 250 sec) departure from linearity in the eclipse times of QS Vir which Applegate's mechanism fails to reproduce by an order of magnitude. The only mechanism able to drive this period change is a third body in a highly elliptical orbit. However, the planetary/sub-stellar companion previously suggested to exist in this system is ruled out by our data. Our eclipse times show that the period decrease detected in NN Ser is continuing, with magnetic braking or a third body the only mechanisms able to explain this change. The planetary/sub-stellar companion previously suggested to exist in NN Ser is also ruled out by our data. Our precise eclipse times also lead to improved ephemerides for DE CVn and GK Vir. The width of a primary eclipse is directly related to the size of the secondary star and variations in the size of this star could be an indication of Applegate's mechanism or Wilson (starspot) depressions which can cause jitter in the O-C curves. We measure the width of primary eclipses for the systems NN Ser and GK Vir over several years but find no definitive variations in the radii of the secondary stars. However, our data are precise enough (dRsec / Rsec < 10^-5) to show the effects of Applegate's mechanism in the future. We find no evidence of Wilson depressions in either system. We also find tentative indications that flaring rates of the secondary stars depend on their mass rather than rotation rates.