MMT超高速恒星巡天III：北Milky Way晕中微弱B型恒星的全面巡天
MMT Hypervelocity Star Survey III: A Complete Survey of Faint B-type Stars in the Northern Milky Way Halo
摘要：
我们描述了我们完成的光谱调查未绑定的超高速恒星（HVS）从银河系喷射。三个新发现使未结合的HVS总数达到21个。我们使用中等分辨率的MMT光谱对HVS的性质及其距离施加了新的限制。一半的HVS是快速旋转的，它们是一些2.5-4 Msun的主序星，距离50 - 120 kpc。修正恒星寿命后，我们的调查表明，未束缚的2.5-4 Msun恒星以1.5e-6 /yr的速率从银河系中被弹射出来。所观测到的HVS可能在过去的2亿年中连续喷出，并且不共享共同的飞行时间。HVS在天空中的各向异性空间分布仍然令人困惑。像SkyMapper这样的南半球调查将很快使我们能够绘制HVS的全天分布图。未来用哈勃太空望远镜和盖亚进行的自行测量将对起源提供强有力的约束。所有现有的观测结果都与银河系中心大质量黑洞遭遇时的HVS喷射相一致。
英文摘要：
We describe our completed spectroscopic survey for unbound hypervelocity stars (HVSs) ejected from the Milky Way. Three new discoveries bring the total number of unbound HVSs to 21. We place new constraints on the nature of HVSs and on their distances using moderate resolution MMT spectroscopy. Half of the HVSs are fast rotators; they are certain 2.5-4 Msun main sequence stars at 50 - 120 kpc distances. Correcting for stellar lifetime, our survey implies that unbound 2.5-4 Msun stars are ejected from the Milky Way at a rate of 1.5e-6 /yr. The observed HVSs are likely ejected continuously over the past 200 Myr and do not share a common flight time. The anisotropic spatial distribution of HVSs on the sky remains puzzling. Southern hemisphere surveys like SkyMapper will soon allow us to map the all-sky distribution of HVSs. Future proper motion measurements with Hubble Space Telescope and Gaia will provide strong constraints on origin. All existing observations are consistent with HVS ejections from encounters with the massive black hole in the Galactic center.
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