AI 中文总结
研究发现原型矮新星U Gem周围存在两个同心H-alpha亮壳，其可能对应约1000年前的新星抛射物，中国唐代记录的客星或为该新星，但日韩无相关记录存疑。
AI 中文摘要
自被发现以来的170年间，U Gem作为典型的激变双星被深入研究。其质量约为1.2倍太阳质量的白矮星（WD）正在吞噬质量约为0.42倍太阳质量的红矮星伴星。白矮星由此吸积的富氢包层此前经历了热核失控，表现为持续数周、亮度达到视星等m~-3的新星爆发，并以数千千米每秒的速度抛射出约0.00001倍太阳质量的吸积包层。紫外观测显示，U Gem白矮星的吸积包层氮含量相对于太阳组成大幅增强，碳含量则大幅耗尽，且该白矮星的有效温度远高于大多数激变双星中的白矮星。这些特征表明U Gem近期经历了一次经典新星爆发，因此其周围应仍存在该事件的抛射物。对U Gem的模型预测显示，其约在1000年前发生过一次新星事件，且周围存在两个大小各约1度的同心壳层。我们使用Condor Array Telescope获得了U Gem的深场窄带H-alpha成像，发现以U Gem为中心的两个同心H-alpha亮壳层，可能是首个被预测到的古老新星抛射物。中国古代星象学家在公元829年11月记录的“水尾”星官中的 transient“客星”，与U Gem最后一次预测的新星爆发的时间和位置一致，但该瞬变源未出现在日本和韩国的记录中，这对上述推测不利。
英文摘要
In the 170 years since its discovery, U Gem has been intensively studied as the prototypical cataclysmic binary star. Its massive white dwarf (WD) (~ 1.2 Msun) is cannibalizing its ~ 0.42 Msun red dwarf companion. The WD's resulting accreted hydrogen-rich envelope has previously undergone thermonuclear runaways seen as nova eruptions. These weekslong transient events brighten U Gem to m ~ -3 and eject the accreted envelope (~ 0.00001 Msun) at thousands of km/s. Ultraviolet observations show that the accreted envelope of U Gem's WD is greatly enhanced in nitrogen and depleted in carbon relative to solar composition, and that the WD's effective temperature is much hotter than that of most cataclysmic binary WDs. These suggest that U Gem underwent a classical nova eruption quite recently and should therefore still be surrounded by the ejecta of that event. Modeling of U Gem predicts a nova event ~ 1000 years ago, and the existence of two concentric shells, each of order 1 degree in size, surrounding U Gem. We obtained deep narrowband H-alpha imaging of U Gem with the Condor Array Telescope. The two concentric H-alpha-bright shells that we find, centered on U Gem, may be the first-ever predicted old nova ejecta. A transient "guest star" in the asterism Shuiwei, recorded by Chinese imperial astrologers in November 829 CE is consistent with the timing and location of U Gem's last predicted nova eruption, but the transient's absence in Japanese and Korean records weighs against this suggestion.
Comments14 pages, 7 figures
