在盖亚DR2中发现的星际物体“Oumuamua”的可能母星
Plausible home stars of the interstellar object 'Oumuamua found in Gaia DR2
摘要：
第一个被发现的星际物体Oumuamua于2017年9月9日在距离太阳0.25天文单位的范围内通过，据推测是从恒星系统中喷射出来的。我们使用它新确定的非开普勒轨道，以及来自盖亚DR 2的700万颗恒星的重建银河系轨道来识别过去的近距离接触。这样的“遭遇”可能会揭示“Oumuamua”被驱逐出的家园系统。最近的一次相遇，在0.60秒差距（0.53- 0.67秒差距，90%置信区间），是在100万年前与M2.5矮星HIP 3757相遇，相对速度为24.7公里/秒。一个更远的相遇（1.6pc），但以10.7km/s的较低相遇（喷射）速度与G5矮星HD 292249相遇，380万年前。另外两颗恒星的相遇距离和速度都在这两者之间。在“Oumuamua”的六个不同的非引力轨道上，遭遇参数是相似的。在其中一个系统中，'Oumuamua被一颗巨大的行星散射而抛射出来是合理的，但需要一个相当不可能的配置来实现所发现的高速度。双星系统更有可能产生所观察到的速度。四个候选者中没有一个发表过系外行星或已知是双星。考虑到盖亚DR 2中具有6D相空间信息的700万颗恒星只是我们最终可以重建轨道的所有恒星的一小部分，我们目前的搜索不太可能找到Oumuamua的母星系统。由于'Oumuamua预计每百万年会在大约20颗恒星和棕矮星的1 pc范围内通过，因此家庭系统的可扩展性也取决于适当的（低）遭遇速度。
英文摘要：
The first detected interstellar object 'Oumuamua that passed within 0.25au of the Sun on 2017 September 9 was presumably ejected from a stellar system. We use its newly determined non-Keplerian trajectory together with the reconstructed Galactic orbits of 7 million stars from Gaia DR2 to identify past close encounters. Such an "encounter" could reveal the home system from which 'Oumuamua was ejected. The closest encounter, at 0.60pc (0.53-0.67pc, 90% confidence interval), was with the M2.5 dwarf HIP 3757 at a relative velocity of 24.7km/s, 1Myr ago. A more distant encounter (1.6pc) but with a lower encounter (ejection) velocity of 10.7km/s was with the G5 dwarf HD 292249, 3.8Myr ago. Two more stars have encounter distances and velocities intermediate to these. The encounter parameters are similar across six different non-gravitational trajectories for 'Oumuamua. Ejection of 'Oumuamua by scattering from a giant planet in one of the systems is plausible, but requires a rather unlikely configuration to achieve the high velocities found. A binary star system is more likely to produce the observed velocities. None of the four home candidates have published exoplanets or are known to be binaries. Given that the 7 million stars in Gaia DR2 with 6D phase space information is just a small fraction of all stars for which we can eventually reconstruct orbits, it is a priori unlikely that our current search would find 'Oumuamua's home star system. As 'Oumuamua is expected to pass within 1pc of about 20 stars and brown dwarfs every Myr, the plausibility of a home system depends also on an appropriate (low) encounter velocity.
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