The bulge is the oldest component of the Milky Way. Since numerous simulations of Milky Way formation have predicted that the oldest stars at a given metallicity are found on tightly bound orbits, the Galaxy's oldest stars are likely metal-poor stars in the inner bulge with small apocenters (i.e., $R_{\mathrm{apo}}\lesssim4$ kpc). In the past, stars with these properties have been impossible to find due to extreme reddening and extinction along the line of sight to the inner bulge. We have used the mid-infrared metal-poor star selection of Schlaufman & Casey (2014) on Spitzer/GLIMPSE data to overcome these problems and target candidate inner bulge metal-poor giants for moderate-resolution spectroscopy with AAT/AAOmega. We used those data to select three confirmed metal-poor giants ($[\mathrm{Fe/H}]=-3.15,-2.56,-2.03$) for follow-up high-resolution Magellan/MIKE spectroscopy. A comprehensive orbit analysis using Gaia DR2 astrometry and our measured radial velocities confirms that these stars are tightly bound inner bulge stars. We determine the elemental abundances of each star and find high titanium and iron-peak abundances relative to iron in our most metal-poor star. We propose that the distinct abundance signature we detect is a product of nucleosynthesis in the Chandrasekhar-mass thermonuclear supernova of a CO white dwarf accreting from a helium star with a delay time of about 10 Myr. Even though chemical evolution is expected to occur quickly in the bulge, the intense star formation in the core of the nascent Milky Way was apparently able to produce at least one Chandrasekhar-mass thermonuclear supernova progenitor before chemical evolution advanced beyond $[\mathrm{Fe/H}]\sim-3$.

中文翻译：

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内凸起中金属含量最高的恒星

凸起是银河系最古老的组成部分。由于对银河系形成的大量模拟预测，在给定金属丰度的最古老恒星是在紧密结合的轨道上发现的，因此银河系最古老的恒星很可能是内部凸起中具有小顶点的贫金属恒星（即，$R_{\mathrm{ apo}}\lesssim4$ kpc）。在过去，由于沿视线到内部凸起的极度红化和灭绝，因此无法找到具有这些特性的恒星。我们在 Spitzer/GLIMPSE 数据上使用 Schlaufman & Casey (2014) 的中红外贫金属恒星选择来克服这些问题，并利用 AAT/AAOmega 将候选的内部膨胀金属贫乏巨星定位为中等分辨率光谱。我们使用这些数据选择了三个已确认的贫金属巨头 ($[\mathrm{Fe/H}]=-3.15,-2.56,-2. 03$) 用于后续高分辨率麦哲伦/迈克光谱。使用 Gaia DR2 天体测量和我们测量的径向速度进行的综合轨道分析证实，这些恒星是紧密结合的内部膨胀恒星。我们确定每颗恒星的元素丰度，并在我们最缺乏金属的恒星中找到相对于铁的高钛和铁峰丰度。我们提出，我们检测到的独特丰度特征是从一颗氦星以大约 10 Myr 的延迟时间吸积的 CO 白矮星的钱德拉塞卡质量热核超新星中核合成的产物。尽管预计化学演化会在凸起中迅速发生，