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SDSSJ0018-0939：亚钱德拉塞卡质量Ia型超新星的清晰特征

SDSSJ0018-0939: A Clear Signature of Sub-Chandrasekhar Mass Type 1a Supernova

S. K. Jeena, Projjwal Banerjee

备注：
14 pages, 4 figures, 2 tables. Submitted to journal
发表信息：
The Astrophysical Journal, 2024, 975, 108
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AI总结：

本研究通过分析极贫金属星形成通道，发现α贫VMP星SDSSJ0018-0939是亚钱德拉塞卡质量Ia型超新星的清晰特征，验证了早期星系中该类超新星占主导的结论。

摘要：

极贫金属（VMP）星（${\rm [Fe/H]}\leq -2$）若其镁、硅、钙等α元素的${\rm [X/Fe]}$值低于太阳值，则被称为α贫VMP星。这类恒星在VMP星中相当罕见，据信它们主要由单次Ia型超新星（SN1a）增丰的气体形成，而大多数VMP星为α增丰型，通常与核坍缩超新星相关。这类恒星中观测到的丰度模式可为研究单个SN1a的核合成过程提供直接途径。尽管部分α贫VMP星的丰度模式已被证明与SN1a抛射物一致，但由近钱德拉塞卡质量（near-${\rm M_{Ch}}$）或亚钱德拉塞卡质量（sub-${\rm M_{Ch}}$）白矮星爆炸产生的SN1a的明确核合成特征，尚未被明确探测到。我们对VMP星的各种形成通道开展了详细分析，发现此前被报道可能起源于对不稳定超新星的α贫VMP星SDSSJ0018-0939，几乎是氦爆轰引发的sub-${\rm M_{Ch}}$ SN1a的确凿特征。我们发现，与此前被认定与SN1a相关的其他α贫VMP星相比，SDSSJ0018-0939是唯一一颗具有清晰、明确SN1a特征的恒星。值得注意的是，我们的结果与近期银河系化学演化研究对SN1a的约束一致，这些研究表明sub-${\rm M_{Ch}}$ SN1a占所有SN1a的约50-75%，可能是早期宇宙中占主导地位的SN1a形成通道。

英文摘要：

Very metal-poor (VMP) stars (${\rm [Fe/H]}\leq -2$) that have sub-solar values of ${\rm [X/Fe]}$ for $α$ elements such as Mg, Si, and Ca, are referred to as $α$-poor VMP stars. They are quite rare among VMP stars and are thought to have formed from gas enriched predominantly by a single Type Ia supernovae (SN1a) in contrast to most VMP stars which are $α$-enhanced and usually associated with core-collapse supernovae. The observed abundance pattern in such stars can provide a direct way to probe the nucleosynthesis in individual SN1a. Although the abundance patterns in some $α$-poor VMP stars have been shown to be consistent with SN1a ejecta, a clear nucleosynthetic signature for SN1a resulting from the explosion of a near Chandrasekhar mass (near-${\rm M_{Ch}}$) or a sub-Chandrasekhar mass (sub-${\rm M_{Ch}}$) white dwarf, has not been unambiguously detected. We perform a detailed analysis of various formation channels of VMP stars and find that the $α$-poor VMP star SDSSJ0018-0939, which was earlier reported as a star with potential pair-instability supernova origin, provides almost a smoking-gun signature of a sub-${\rm M_{Ch}}$ SN1a resulting from He detonation. We find that compared to other $α$-poor VMP stars that were previously identified with SN1a, SDSSJ0018-0939 is the only star that has a clear and unambiguous signature of SN1a. Interestingly, our results are consistent with constraints on SN1a from recent galactic chemical evolution studies that indicate that sub-${\rm M_{Ch}}$ SN1a account for $\sim 50\hbox{--}75\,\%$ of all SN1a and are possibly the dominant channel in the early Galaxy.

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