Abundance patterns of α and neutron-capture elements in the helmi stream
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2021
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We identified eight additional stars as members of the Helmi stream (HStr) in the combined GALAH+ DR3 and
Gaia EDR3 catalog. By consistently reevaluating claimed members from the literature, we consolidate a sample of
22 HStr stars with parameters determined from high-resolution spectroscopy and spanning a considerably wider
(by ∼0.5 dex) metallicity interval (− 2.5 [Fe/H] < − 1.0) than previously reported. Our study focuses on α (Mg
and Ca) and neutron-capture (Ba and Eu) elements. We find that the chemistry of HStr is typical of dwarf
spheroidal (dSph) galaxies, in good agreement with previous N-body simulations of this merging event. Stars of
HStr constitute a clear declining sequence in [α/Fe] for increasing metallicity up to [Fe/H] ∼ −1.0. Moreover,
stars of HStr show a median value of +0.5 dex for [Eu/Fe] with a small dispersion (±0.1 dex). Every star analyzed
with [Fe/H] < −1.2 belongs to the r-process enhanced ([Eu/Fe] > +0.3 and [Ba/Eu] < 0.0) metal-poor category,
providing remarkable evidence that, at such a low-metallicity regime, stars of HStr experienced enrichment in
neutron-capture elements predominantly via r-process nucleosynthesis. Finally, the extended metallicity range also
suggests an increase in [Ba/Eu] for higher [Fe/H], in conformity with other surviving dwarf satellite galaxies of
the Milky Way.
Unified Astronomy
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LIMBERG, Guilherme et al. Abundance patterns of α and neutron-capture elements in the helmi stream. Astrophysical Journal Letters, Bristol, v. 913, n. 2, e28, 2021. DOI: 10.3847/2041-8213/ac0056. Disponível em: https://iopscience.iop.org/article/10.3847/2041-8213/ac0056.m. Acesso em: 11 maio 20.