论文标题
早期银河化学富集的不均匀性，由极为金属贫困的恒星中的铍丰度暴露
Inhomogeneity in the early Galactic chemical enrichment exposed by beryllium abundances in extremely metal-poor stars
论文作者
论文摘要
金属贫困恒星中铍的丰度与金属度线性缩放至[Fe/H]〜 -3.0。在这种极为贫穷的恒星中检测到的恒星中，先前已经报道了丰度增加。这种散射可能表明BE和[Fe/H]之间的关系存在平坦。我们的目的是对极为贫困的明星中的丰富性进行新的调查，并试图阐明是否存在丰富的高原。我们在[Fe/H]〜 -3.0的九个矮人样本中重新审视了丰富的体重。此外，我们首次分析了恒星BPS BS 16968-0061和CD-33 1173中的BE线。我们利用Gaia DR2视差来完善恒星表面重力的值。使用光谱合成确定BE的丰度。一些恒星确实暗示着变平。在[fe/h]〜 -2.70和-3.26之间，be beundances在log（be/h）〜 -13.2 dex中大部分保持恒定。然而，对于几个恒星，我们只能将高于该水平的上限放置。大多数样品恒星与所谓的Gaia-enceladus合并的祖细胞形成一致。可能形成原位的三个恒星中有两颗是偏离线性关系的恒星。这些恒星的混合起源为理解扁平化提供了线索。我们建议我们的观察结果可以理解是由于早期星系中不均匀的恒星形成条件的结果。没有有效的混合，早期的ISM的特征是在给定时刻的Fe丰度大量散射。另一方面，由于其起源于宇宙射线散布，它将具有更大的均匀丰富性（从星系范围内的意义上）。因此，我们建议观察到的Be-vers-FE关系的扁平化反映了给定年龄的银河系丰度的散布[删节]。
Abundances of beryllium in metal-poor stars scale linearly with metallicity down to [Fe/H] ~ -3.0. In the stars where Be has been detected at this extremely metal-poor regime, an increased abundance scatter has been previously reported. This scatter could indicate a flattening of the relation between Be and [Fe/H]. Our aim is to perform a new investigation of Be abundances in extremely metal-poor stars and try to clarify whether a Be abundance plateau exists. We revisited the Be abundances in a sample of nine dwarfs with [Fe/H] ~ -3.0. Additionally, we analysed the Be lines in the spectra of stars BPS BS 16968-0061 and CD-33 1173 for the first time. We took advantage of Gaia DR2 parallaxes to refine values of the surface gravity of the stars. Abundances of Be were determined using spectrum synthesis. Some of the stars indeed suggest a flattening. Between [Fe/H] ~ -2.70 and -3.26, the Be abundances stay mostly constant at log(Be/H) ~ -13.2 dex. Nevertheless, for several stars we could only place upper limits that are below that level. Most of the sample stars are consistent with having been formed at the progenitor of the so-called Gaia-Enceladus merger. Two out of the three stars likely formed in-situ are the ones that deviate the most from the linear relation. The mixed origin of these stars offers a clue to understanding the flattening. We suggest that our observations can be understood as a consequence of the inhomogeneous star forming conditions in the early Galaxy. Without efficient mixing, the early ISM would be characterised by a large scatter in Fe abundances at a given moment. Beryllium, on the other hand, because of its origins in cosmic-ray spallation, would have more homogeneous abundances (in a Galaxy-wide sense). We therefore suggest that the observed flattening of the Be-versus-Fe relation reflects a stronger scatter in the Galactic Fe abundances at a given age [abridged].
