Abundance Patterns of α and Neutron-capture Elements in the Helmi Stream

Abstract 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 spectroscop...

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Bibliographic Details
Published in:	Astrophysical journal. Letters 2021-06, Vol.913 (2), p.L28
Main Authors:	Limberg, Guilherme, Santucci, Rafael M., Rossi, Silvia, Queiroz, Anna B. A., Chiappini, Cristina, Souza, Stefano O., Perottoni, Hélio D., Pérez-Villegas, Angeles, Barbosa, Fabrícia O.
Format:	Article
Language:	eng
Subjects:	Barium Chemical abundances Dwarf galaxies Galaxies Iron Metallicity Milky Way Milky Way dynamics Milky Way evolution Milky Way formation Milky Way stellar halo Nuclear capture Nuclear fusion Population II stars R-process Spectroscopy Stars Stars & galaxies Stellar populations
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Summary:	Abstract 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.
ISSN:	2041-8205 2041-8213