论文标题
超安全矮星系的S过程
s-process Enirchment of Ultrafaint Dwarf Galaxies
论文作者
论文摘要
我们研究超级矮星系（UFDS）中钡（BA）和锶（SR）的产生。 R-和S-过程都会产生这些元素，并且可以从特征性的R-过程丰度模式中推断出R过程的贡献，而S过程的贡献仍然在很大程度上未知。我们表明，渐近巨型分支（AGB）恒星的当前S过程不足以解释UFD中观察到的BA和SR丰度。从星系中的恒星形成开始，这些元素的产生将需要有效。即使我们考虑在超级AGB恒星中的S过程，几乎或大于1个DEX的差异也不会调和。我们将可能的分辨率视为旋转巨大的恒星（RMS）和电子捕获超新星（ECSNE）作为其他贡献者。我们发现，如果约有10％的大恒星在300 km S^{ - 1}旋转，则RMS可以是UFD中BA的起源。至于Ecsne，我们认为它们的分数不到核心折叠超新星的2％。它将祖先质量范围缩小到-3 <[fe/h] <-2时<0.1 msun。我们还通过修改UFD中的出色初始质量函数（IMF），并找到一个重现观察到的BA富集水平的顶级IMF模型来探索另一种分辨率。确定或严格限制Europium和氮丰度的未来观察对于确定UFD中BA和SR的起源至关重要。
We study the production of barium (Ba) and strontium (Sr) in ultrafaint dwarf galaxies (UFDs). Both r- and s- processes produce these elements, and one can infer the contribution of the r-process from the characteristic r-process abundance pattern, whereas the s-process contribution remains largely unknown. We show that the current s-process yield from asymptotic giant branch (AGB) stars is not sufficient to explain the Ba and Sr abundances observed in UFDs. Production of these elements would need to be efficient from the beginning of star formation in the galaxies. The discrepancy of nearly or more than 1 dex is not reconciled even if we consider s-process in super-AGB stars. We consider a possible resolution by assuming rotating massive stars (RMSs) and electron-capture supernovae (ECSNe) as additional contributors. We find that the RMSs could be the origin of Ba in UFDs if ~ 10 per cent of massive stars are rotating at 300 km s^{-1}. As for ECSNe, we argue that their fraction is less than 2 per cent of core-collapse supernova. It narrows the progenitor mass-range to < 0.1 Msun at -3 < [Fe/H] < -2. We also explore another resolution by modifying the stellar initial mass function (IMF) in UFDs and find a top-light IMF model that reproduces the observed level of Ba-enrichment. Future observations that determine or tightly constrain the europium and nitrogen abundances are crucial to identify the origin of Ba and Sr in UFDs.
