GHOST调试科学结果II：一颗见证银河系早期组装的极贫金属恒星
GHOST Commissioning Science Results II: a very metal-poor star witnessing the early Galactic assembly
AI总结：
研究利用GHOST观测PIGS中的极贫金属恒星P180956，通过其元素丰度与轨道特征推断它形成于早期被吸积的超暗矮星系样系统。
摘要：
本研究聚焦于Pristine_180956.78−294759.8（以下简称P180956，[Fe/H]=−1.95±0.02），这是一颗从Pristine Inner Galaxy Survey（PIGS）中选出的恒星，并利用近期在Gemini South望远镜完成调试的Gemini High-resolution Optical SpecTrograph（GHOST）进行了后续观测。GHOST光谱仪在蓝色光谱区（3700–4800 Å）的高效率，使其能够探测早期超新星的元素示踪物（例如Al、Mn、Sr、Eu）。该恒星表现出类似于超暗矮星系系统中所见的化学特征，其特点是中子俘获元素（Sr、Ba、Eu）丰度非常低，这在银河系银晕恒星中并不常见。我们的分析表明，P180956带有少量（2或4个）低质量超超新星（约10–15 M⊙）的化学印记，这些恒星是大体重现轻元素丰度模式（例如[Si, Ti/Mg, Ca]约为0.6）所必需的；同时还带有一颗快速旋转的大质量超新星（约300 km s−1，约80–120 M⊙）的印记，这是造成高[Sr/Ba]（约+1.2）的主要渠道。约0.7 kpc的小近心距和约13 kpc的远心距，以及其局限于银道面（≲2 kpc）的轨道，表明这颗恒星很可能是在银河系早期组装阶段被吸积的。其化学—动力学性质表明，P180956形成于一个类似超暗矮星系的系统中，该系统要么作为原银河系的低质量组成单元之一被单独吸积，要么作为Gaia-Sausage-Enceladus的卫星被吸积。Gemini的大口径与GHOST的高效率和宽光谱覆盖相结合，使这台新光谱仪成为近场宇宙学研究的领先仪器之一。
英文摘要：
This study focuses on Pristine$\_180956.78$$-$$294759.8$ (hereafter P180956, $[Fe/H] =-1.95\pm0.02$), a star selected from the Pristine Inner Galaxy Survey (PIGS), and followed-up with the recently commissioned Gemini High-resolution Optical SpecTrograph (GHOST) at the Gemini South telescope. The GHOST spectrograph's high efficiency in the blue spectral region ($3700-4800$~Å) enables the detection of elemental tracers of early supernovae (\eg Al, Mn, Sr, Eu). The star exhibits chemical signatures resembling those found in ultra-faint dwarf systems, characterised by very low abundances of neutron-capture elements (Sr, Ba, Eu), which are uncommon among stars in the Milky Way halo. Our analysis suggests that P180956 bears the chemical imprints of a small number (2 or 4) of low-mass hypernovae ($\sim10-15 M_{\odot}$), which are needed to mostly reproduce the abundance pattern of the light-elements (\eg [Si, Ti/Mg, Ca] $\sim0.6$), and one fast-rotating intermediate-mass supernova ($\sim300\kms$, $\sim80-120 M_{\odot}$), which is the main channel contributing to the high [Sr/Ba] ($\sim +1.2$). The small pericentric ($\sim0.7$ kpc) and apocentric ($\sim13$ kpc) distances and its orbit confined to the plane ($\lesssim 2$ kpc), indicate that this star was likely accreted during the early Galactic assembly phase. Its chemo-dynamical properties suggest that P180956 formed in a system similar to an ultra-faint dwarf galaxy accreted either alone, as one of the low-mass building blocks of the proto-Galaxy, or as a satellite of Gaia-Sausage-Enceladus. The combination of Gemini's large aperture with GHOST's high efficiency and broad spectral coverage makes this new spectrograph one of the leading instruments for near-field cosmology investigations.
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