Chemical Abundance Signature of J0023+0307: A Second-generation Main-sequence Star with [Fe/H] < −6
Chemical Abundance Signature of J0023+0307: A Second-generation Main-sequence Star with [Fe/H] < −6
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DOI：
10.3847/1538-4357/aae848
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发表时间：
2018-10
期刊：
影响因子：
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通讯作者：
A. Frebel;A. Ji;R. Ezzeddine;T. Hansen;A. Chiti;I. Thompson;T. Merle
中科院分区：
文献类型：
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作者：
A. Frebel;A. Ji;R. Ezzeddine;T. Hansen;A. Chiti;I. Thompson;T. Merle
我们基于高分辨率（R = 35，000）麦哲伦/MIKE光谱，对微弱的晕贫金属主序星星星J 0023 +0307进行了化学丰度分析，[Fe/H] < −6.3。这颗星星最初被发现[Fe/H] < −6.6，是基于R 2500光谱中的Ca ii K测量。在我们的MIKE光谱中没有检测到铁谱线。检测到Li、C、Na、Mg、Al、Si和Ca的谱线。Li丰度接近Spite Plateau，（Li）= 1.7，与其他贫金属恒星不同，尽管与发现的极低值形成鲜明对比，例如，在HE 1327-2326中以类似的[Fe/H]值。碳G带被探测到，并显示出强烈的C增强，这是典型的低铁丰度的恒星。从Na到Si的元素显示出强烈的奇偶效应，J 0023 +0307显示出第二低的[Ca/H]丰度。总的来说，J 0023 +0307的丰度模式表明它是一颗第二代星星，是由一颗大质量的第三星族第一颗星星作为后备超新星爆炸而富集的气体形成的。喷出物的稀释质量为105±0.5 M H2O，强烈表明J 0023 +0307形成于一个消失的微晕。J 0023 +0307很可能非常古老，因为它的轨道非常偏心，近心点位于银河系凸起。
We present a chemical abundance analysis of the faint halo metal-poor main-sequence star J0023+0307, with [Fe/H] < −6.3, based on a high-resolution (R ∼ 35,000) Magellan/MIKE spectrum. The star was originally found to have [Fe/H] < −6.6 based on a Ca ii K measurement in an R ∼ 2500 spectrum. No iron lines could be detected in our MIKE spectrum. Spectral lines of Li, C, Na, Mg, Al, Si, and Ca were detected. The Li abundance is close to the Spite Plateau, (Li) = 1.7, not unlike that of other metal-poor stars, although in stark contrast to the extremely low value found, e.g., in HE 1327–2326 at a similar [Fe/H] value. The carbon G-band is detected and indicates strong C-enhancement, as is typical for stars with low Fe abundances. Elements from Na through Si show a strong odd–even effect, and J0023+0307 displays the second-lowest known [Ca/H] abundance. Overall, the abundance pattern of J0023+0307 suggests that it is a second-generation star that formed from gas enriched by a massive Population III first star exploding as a fallback supernova. The inferred dilution mass of the ejecta is 105±0.5 M⊙ of hydrogen, strongly suggesting J0023+0307 formed in a recollapsed minihalo. J0023+0307 is likely very old because it has a very eccentric orbit with a pericenter in the Galactic bulge.