Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 496, Issue 3, Pages 2902-2909Publisher
OXFORD UNIV PRESS
DOI: 10.1093/mnras/staa1653
Keywords
stars: abundances; Galaxy: halo; Galaxy: stellar content; galaxies: abundances; galaxies: individual: Gaia-Enceladus; primordial nucleosynthesis
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Funding
- EU COST Action [CA16117]
- National Natural Science Foundation of China [11973001]
- National Key Research and Development Program of China [2019YFA0405504]
- Australian Astronomical Observatory [A/2013B/13, A/2014A/25, A/2015A/19, A/2017A/18]
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Data from Gaia DR2 and The Apache Point Observatory Galactic Evolution Experiment 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 Gyr 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-7 and Be-9 in dwarf stars that are out of reach even in Local Group galaxies. Searching in GALAH, Gaia-ESO survey and in literature, we found several existing Li-7 abundance determinations of stars belonging to the Gaia-Enceladus galaxy. The Li-7 abundances of stars at the low metallicity end overlap with those of the Galactic halo. These are effective extragalactic Li-7 measurements, which suggest that the Li-7 Spite plateau is universal, as is the cosmological Li-7 problem. We found a Li-7-rich giant out of 101 stars, which suggests a small percentage similar to that of the Milky Way. We also collect Be-9 abundance 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 Be-9 evolution patterns of different stellar components that are mixed-up in the Galactic halo.
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