高速恒星 II：一颗未束缚恒星、年轻恒星、核球贫金属恒星及 Aurora 候选体
High-speed stars. II. An unbound star, young stars, bulge metal-poor stars, and Aurora candidates
AI总结：
基于盖亚数据，利用化学与动力学性质分类高速恒星，发现一颗未束缚的落入恒星、年轻贫金属星族、核球贫金属星族 SpiteF 及 102 个 Aurora 候选体，揭示银河系结构新认知。
摘要：
盖亚卫星的数据促使我们修正了对银河系结构和历史的认知。迄今未知的组分被发现，对银河系晕的深入反思正在进行中。我们从盖亚星表中挑选出相对于太阳具有极端横向速度（|V_T| > 500 km/s）的恒星，并使用 ESO VLT 上的 FORS2 仪器进行观测，以通过化学和动力学性质对它们进行分类。论文 I 中识别的两颗明显年轻的恒星，使用 UVES 进行了观测。我们推导了 Na、Mg、Ca、Ti、Mn 和 Fe 的丰度，通过分析光谱得到，而 Ba 则使用谱线轮廓拟合。我们根据视差和运动学数据计算了作用量。这些恒星跨越的金属丰度范围为 [Fe/H] = -0.5 至 [Fe/H] = -1.6。恒星 GHS143 的总速度约为 1440 km/s，几乎是当地逃逸速度 522 km/s 的三倍，强烈表明该恒星未束缚于银河系。值得注意的是，这颗恒星并非正在逃离银河系，而是正在落入其中。十颗恒星明显年轻，质量超过 1.3 倍太阳质量。将它们解释为演化后的蓝离散星是可疑的。存在年轻贫金属星族的可能性是存在的。用 UVES 观测的两颗恒星未显示锂，表明它们是蓝离散星。我们探测到一个局限于核球的贫金属星族，称之为 SpiteF，并认为它是近期吸积事件的结果。我们探测到 102 个 Aurora 星族候选体，它们应形成于银盘形成之前。我们的样本是非均匀的，且主要为逆行轨道。这些恒星是贫金属的，其中 23% 的 [Fe/H] < -2.0。我们的选择方法在寻找极贫金属恒星方面是高效的，但它也选出了特殊星族。
英文摘要：
The data from the Gaia satellite led us to revise our conception of the Galaxy structure and history. Hitherto unknown components have been discovered and a deep re-thinking of what the Galactic halo is is in progress. We selected from the Gaia catalogue stars with extreme transverse velocities with respect to the Sun ($|V_T| > 500 $ and observed them with FORS2 at the ESO VLT, to classify them using both their chemical and dynamical properties. Two apparently young stars, identified in paper\,I, were observed with UVES. We derived abundances for Na, Mg, Ca, Ti, Mn, and Fe, analysing the spectra with while for Ba we used line profile fitting. We computed actions from parallaxes and kinematical data. The stars span the metallicity range $ Fe/H -0.5$ with $ Fe/H = -1.6$. Star GHS143 has a total speed of about 1440 which is almost three times faster than the local escape velocity of 522 strongly implying this star is unbound to the Galaxy. Remarkably, this star is not escaping from the Galaxy, but it is falling into it. Ten stars are apparently young with masses in excess of 1.3M. Their interpretation as evolved blue stragglers is doubtful. The existence of a young metal-poor population is possible. The two stars observed with UVES show no lithium, suggesting they are blue stragglers. We detected a metal-poor population, confined to the bulge, that we call SpiteF, and argue that it is the result of a recent accretion event. We detect 102 candidates of the Aurora population that should have formed prior to the formation of the disc. Our sample is non-homogeneous and mainly retrograde. The stars are metal poor, and 23<!PCT!> have Fe/H -2.0$. Our selection is efficient at finding very metal-poor stars, but it selects peculiar populations.
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