共生星AG天龙座的历史光变曲线：强烈的磁感应周期活动
The historical light curve of the symbiotic star AG Draconis: intense, magnetically induced cyclic activity
摘要：
我们分析了共生系统AG Draconis的光学光变曲线，涵盖了它过去120年的历史。在最初的32年里，系统处于静止状态。在1922年左右，恒星的平静光度增亮了0.29等。光变曲线（LC）的最后82年的特征是一系列亮度为1-2等的爆发，持续时间约为100天。爆发沿时间轴分布在6个集群与准周期约5300天的周期。爆发的时间间隔是373.5天的整数倍。在静止状态下，LC以550 d的系统的二进制周期振荡。LC还包含一个弱的周期信号，周期为350 d，归因于巨星的脉动。另一个1160 d的周期也出现在光变曲线中，这是巨星的恒星自转周期。我们认为，爆发是强烈的质量转移的事件从巨人到热组件。这些都是由一个类似太阳的磁发电机循环在巨人的外层，和这些层的潮汐变形之间的相互作用，循环与373.5地球日的会合日周期的巨人的表面调制。AG Dra是第五个共生系统，其光变曲线反映了如此强烈的磁场和磁调制活动。（节录）
英文摘要：
We analyze an optical light curve of the symbiotic system AG Draconis covering the last 120 years of its history. During the first 32 years the system was in a quiescence state. Around the year 1922 the star's quiescence luminosity brightened by 0.29 mag. The last 82 years of the light curve (LC) are characterized by a series of outbursts of 1-2 magnitude in brightness and about 100 days in duration. The outbursts are distributed along the time axis in 6 clusters with a quasi-periodic cycle of some 5300 days. The time intervals among the outbursts themselves are integral numbers of the period 373.5 days. During quiescence states the LC oscillates with the binary period of the system of 550 d. The LC contains also a weak periodic signal with a period of 350 d, attributed to pulsations of the giant star. Another period of 1160 d is also present in the light curve, being the sidereal rotation period of the giant star. We suggest that the outbursts are events of intense mass transfer from the giant onto the hot component. These are modulated by an interplay between a solar-like magnetic dynamo cycle operating in the outer layers of the giant, and a tidal deformation of these layers that circulates the surface of the giant with the synodic diurnal period of 373.5 Earth days. AG Dra is the 5th symbiotic system with a light curve that reflects such an intense magnetic and magnetically modulated activity. (Abridged)
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