双子座η：一颗被扩展盘环绕的伴星环绕的半规则变星
Eta Geminorum: An Eclipsing Semiregular Variable Star Orbited by a Companion Surrounded by an Extended Disc
摘要：
我们报告了对M型渐近巨星分支星eta Gem的11年光谱监测。eta Gem是一颗半正则变星，是一颗周期为8.2年的光谱双星。我们结合我们的径向速度与其他文献提供了一个改进的光谱轨道解决方案，给出了一个为期2979天，然后我们用它来预测过去的日食时间。我们检查档案测光从业余变星观测者，和其他来源，并发现许多情况下，在正确的时间发生的调光。这证实了之前的迹象表明，该系统正在日食，它现在是已知周期最长的系统之一。没有看到二次日食。持续约5个月的$\sim$ 0.4等日食太深了，不可能是恒星伴星产生的。相反，我们认为伴星被一个直径至少为1.5天文单位的大圆盘包围，但可能更大。我们预测下一次日食的中心将发生在2029年元旦。
英文摘要：
We report 11 yr of spectroscopic monitoring of the M-type asymptotic giant branch star eta Gem, a semiregular variable and a known spectroscopic binary with a period of 8.2 yr. We combine our radial velocities with others from the literature to provide an improved spectroscopic orbital solution giving a period of 2979 days, which we then use to predict past times of eclipse. We examine archival photometry from amateur variable star observers, and other sources, and find many instances of dimmings that occurred at the right time. This confirms previous indications that the system is eclipsing, and it now ranks among those with the longest known periods. No secondary eclipses are seen. The $\sim$0.4 mag eclipses lasting about 5 months are much too deep to be produced by a stellar companion. We propose instead that the companion is surrounded by a large disk that is at least 1.5 au in diameter, but is likely larger. We predict the center of the next eclipse will occur on New Year's day, 2029.
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