发表机构
INAF – Osservatorio Astrofisico di Arcetri; Institute of Theoretical Physics and Astronomy, Faculty of Physics, Vilnius University（意大利国家天体物理研究所阿切特里天文台; 维尔纽斯大学物理学院理论与天体物理研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究利用GALAH DR4数据发现银河系薄盘中存在年龄高达125亿年的低α元素恒星，表明薄盘形成可能早于预期，并提供星表供后续观测。
AI 中文摘要
$\alpha$元素贫乏的银河系薄盘的形成路径仍存在争议。最新观测数据表明，在低和高$\alpha$盘成分中都存在数量相当的老年恒星，这暗示它们的形成时代要么同时，要么部分重叠。利用GALAH DR4数据，我们提供了证据表明$\alpha$贫乏恒星与$\alpha$丰富恒星共存的时间可追溯至约125亿年。我们利用红外通量法（IRFM）获得的精确有效温度（$T_{\rm{eff}}$）以及基于Gaia视差的距离，为近30,000颗亚巨星重新推导了精度为5亿年的恒星年龄。样本中约22%的恒星构成一个峰值在92亿年的星族，并有证据表明其老年尾部延伸至125亿年。在年龄超过100亿年和110亿年的恒星中，有20%至30%的恒星具有相对较低的[α/Fe]比值和类太阳金属丰度（$-0.5 \leq \mathrm{[Fe/H]} \leq +0.5$ dex）。这些恒星的运动学特征与薄盘中接近太阳年龄的$\alpha$贫乏恒星一致。这些恒星可能是演化后的类太阳恒星，即古老的太阳相似体，其$T_{\rm{eff}}$和引力随时间而改变。与经过充分验证的银河系盘化学演化模型比较，支持存在大量古老的、$\alpha$贫乏的盘恒星，证实了我们选择标准的合理性。我们提供了一个所选样本的星表，以促进高分辨率光谱后续观测。
英文摘要
The formation pathway of the $α$-poor Milky Way thin disc remains under debate. The latest observational data indicates the presence of comparable numbers of old stars in both the low- and high-$α$ disc components, suggesting either coeval or overlapping formation epochs. Using GALAH DR4, we provide evidence that the $α$-poor stars coexist with $α$-rich stars up to $\sim$12.5 Gyr. Stellar ages of 0.5 Gyr precision were re-derived for nearly $30\,000$ subgiant stars using accurate effective temperatures ($T_{\rm{eff}}$) from the infrared flux method (IRFM) together with distances based on Gaia parallaxes. About 22\% of the sample constitutes a population peaking at 9.2 Gyr, with evidence for an extended old-age tail reaching 12.5 Gyr. Among stars older than 10 and 11 Gyr, between 20 and 30\% have relative low [$α$/Fe] and solar-like metallicities ($-0.5 \leq \mathrm{[Fe/H]} \leq +0.5$ dex). These stars exhibit kinematics consistent with those of near solar-age $α$-poor stars in the thin disc. These stars can be evolved Sun-like stars, i.e. old solar analogues, whose $T_{\rm{eff}}$ and gravity modified with the time. Comparison with a well-tested Galactic disc chemical evolution model supports the presence of a significant fraction of old, $α$-poor disc stars, confirming the plausibility of our selection criteria. We provide a catalogue with the selected sample to facilitate spectroscopic follow-ups at high resolution.
CommentsAccepted in A&A
