在类太阳恒星异常宽的轨道上发现$0.2\,M_\odot$白矮星的自透镜现象
Self-lensing Discovery of a $0.2\,M_\odot$ White Dwarf in an Unusually Wide Orbit Around a Sun-like Star
摘要：
我们报告了第五个自透镜双星的发现，其中一个低质量的白矮星（WD）引力放大其15等的G星同伴，KIC 8145411，在日食期间。该系统在开普勒测光中从一对这样的自透镜事件中被识别出来，并在弗雷德·劳伦斯·惠普尔天文台的1.5米望远镜和斯巴鲁8.2米望远镜上的高色散光谱仪（HDS）上进行了跟踪。对TRES径向速度、HDS光谱和开普勒测光的联合分析确定了WD质量$0.20\pm0.01\,M_\odot$、轨道半长轴$1.28\pm0.03\,\mathrm{au}$和轨道偏心率$0.14\pm0.02$。由于这种极低质量的WD不能在银河系的年龄内孤立地形成，因此它们的形成被认为涉及到截断WD祖先进化的二元相互作用。然而，KIC 8145411系统的观测轨道至少比这种情况下所需的宽十倍。这个系统的存在下，在开普勒样本，随着其相似性领域的蓝色离散双星推测含有WD，可能表明，约10%的后AGB双星与太阳一样的原色含有这种异常WD。
英文摘要：
We report the discovery of the fifth self-lensing binary in which a low-mass white dwarf (WD) gravitationally magnifies its 15th magnitude G-star companion, KIC 8145411, during eclipses. The system was identified from a pair of such self-lensing events in the Kepler photometry, and was followed up with the Tillinghast Reflector Echelle Spectrograph (TRES) on the 1.5m telescope at the Fred Lawrence Whipple Observatory and the High-Dispersion Spectrograph (HDS) on the Subaru 8.2m telescope. A joint analysis of the TRES radial velocities, the HDS spectrum, and the Kepler photometry of the primary star determines the WD mass $0.20\pm0.01\,M_\odot$, orbital semi-major axis $1.28\pm0.03\,\mathrm{au}$, and orbital eccentricity $0.14\pm0.02$. Because such extremely low-mass WDs cannot be formed in isolation within the age of the Galaxy, their formation is believed to involve binary interactions that truncated evolution of the WD progenitor. However, the observed orbit of the KIC 8145411 system is at least ten times wider than required for this scenario to work. The presence of this system in the Kepler sample, along with its similarities to field blue straggler binaries presumably containing WDs, may suggest that some 10% of post-AGB binaries with Sun-like primaries contain such anomalous WDs.
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