2021ApJ...913L..28L -
Astrophys. J., 913, L28-L28 (2021/June-1)
Abundance patterns of α and neutron-capture elements in the Helmi stream.
LIMBERG G., SANTUCCI R.M., ROSSI S., QUEIROZ A.B.A., CHIAPPINI C., SOUZA S.O., PEROTTONI H.D., PEREZ-VILLEGAS A. and BARBOSA F.O.
Abstract (from CDS):
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.
Abstract Copyright:
© 2021. The American Astronomical Society. All rights reserved.
Journal keyword(s):
Dwarf galaxies - Milky Way stellar halo - Milky Way dynamics - Milky Way evolution - Milky Way formation - Population II stars - Stellar populations - Chemical abundances - R-process
Simbad objects:
29
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