盖亚-土卫二星系中的锂和铍
Lithium and Beryllium in the Gaia-Enceladus Galaxy
摘要：
来自盖亚DR 2和APOGEE调查的数据揭示了内星系晕中一个相对较新的组成部分，这可能是一个名为盖亚-土卫二的破裂矮星系的动力学残留物，该星系在大约10个Gyrs前与银河系相撞。这一合并事件为研究矮星系中元素的化学丰度提供了一个非凡的机会，因为它们通常在外部星系中受到阻碍。在GALAH、Gaia-ESO巡天和文献中，我们发现了几个现有的Gaia-Enceladus星系中恒星7 Li丰度的测定结果。在低金属丰度端的恒星的7 Li丰度与星系晕的7 Li丰度重叠，这些是有效的河外7 Li测量，这表明{ \it Spite plateau}是普遍存在的，就像宇宙学上的Li问题一样。我们在101颗恒星中发现了一颗富含锂的巨星，这表明与银河系相似的比例很小。我们还收集9 Be丰度的子样本的25盖亚-土卫二恒星的文献。它们的丰度在低金属丰度端与银河系的[Be/H]值相同，但随着[Fe/H]的增加而缓慢增长，并显示出减少的分散。这表明，在银河系中观测到的散射可以反映出混杂在星系晕中的不同恒星成分的不同\beix演化模式。
英文摘要：
Data from Gaia DR2 and APOGEE surveys revealed a relatively new component in the inner Galactic halo, which is likely the dynamical remnant of a disrupted dwarf galaxy named Gaia-Enceladus that collided with the Milky Way about 10 Gyrs ago. This merging event offers an extraordinary opportunity to study chemical abundances of elements in a dwarf galaxy, since they are generally hampered in external galaxies. Here, we focus on Li and Be in dwarf stars which are out of reach even in Local Group galaxies.Searching in GALAH, Gaia-ESO survey and in literature, we found several existing 7Li abundance determinations of stars belonging to the Gaia-Enceladus galaxy. The 7Li abundances of stars at the low metallicity end overlap with those of the Galactic halo.These are effective extragalactic 7Li measurements, which suggest that the {\it Spite plateau} is universal, as is the cosmological Li problem. We found a Li-rich giant out of 101 stars, which suggests a small percentage similar to that of the Milky Way. We also collect 9Be abundances for a subsample of 25 Gaia-Enceladus stars from literature. Their abundances share the Galactic [Be/H] values at the low metallicity end but grow slower with [Fe/H] and show a reduced dispersion. This suggests that the scatter observed in the Milky Way could reflect the different \beix\ evolution patterns of different stellar components which are mixed-up in the Galactic halo.
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