%0 Journal Article %T High-precision chemical abundances of Galactic building blocks. II. Revisiting the chemical distinctness of the Helmi streams %+ Observatoire astronomique de Strasbourg (ObAS) %A Matsuno, Tadafumi %A Dodd, Emma %A Koppelman, Helmer H. %A Helmi, Amina %A Ishigaki, Miho N. %A Aoki, Wako %A Zhao, Jingkun %A Yuan, Zhen %A Hattori, Kohei %< avec comité de lecture %@ 0004-6361 %J Astronomy and Astrophysics - A&A %I EDP Sciences %V 665 %8 2022 %D 2022 %Z 2203.11808 %Z 2022A&A...665A..46M %R 10.1051/0004-6361/202243609 %K Galaxy: abundances %K Galaxy: halo %K stars: abundances %K Galaxy: stellar content %K Astrophysics - Astrophysics of Galaxies %K Astrophysics - Solar and Stellar Astrophysics %Z Sciences of the Universe [physics] %Z Sciences of the Universe [physics]/Astrophysics [astro-ph]Journal articles %X Context. The Helmi streams are a kinematic substructure whose progenitor is likely a dwarf galaxy. Although 20 years have passed since their discovery, it is still unclear whether their members are chemically distinguishable from other halo stars in the Milky Way.
Aims: We aim to precisely characterize the chemical properties of the Helmi streams.
Methods: We analyzed high-resolution, high signal-to-noise ratio spectra for 11 Helmi stream stars through a line-by-line abundance analysis. We compared the derived abundances to homogenized literature abundances of the other halo stars, including those belonging to other kinematic substructures, such as Gaia-Enceladus and Sequoia.
Results: Compared to typical halo stars, the Helmi stream members clearly show low values of [X/Fe] in elements produced by massive stars, such as Na and α-elements. This tendency is seen down to metallicities of at least [Fe/H] ∼ − 2.2, suggesting type Ia supernovae already started to contribute to the chemical evolution at this metallicity. We find that the [α/Fe] ratio does not evolve significantly with metallicity, making the Helmi stream stars less distinguishable from Gaia-Enceladus stars at [Fe/H] ≳ − 1.5. The almost constant but low value of [α/Fe] might be indicative of quiescent star formation with low efficiency at the beginning and bursty star formation at later times. We also find extremely low values of [Y/Fe] at low metallicity, providing further support for the claim that light neutron-capture elements are deficient in Helmi streams. While Zn is deficient at low metallicity, it shows a large spread at high metallicity. The origin of the extremely low Y abundances and Zn variations remains unclear.
Conclusions: The Helmi stream stars are distinguishable from the majority of the halo stars if homogeneously derived abundances are compared.

Full Table 5 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/665/A46 %G English %2 https://insu.hal.science/insu-03781617/document %2 https://insu.hal.science/insu-03781617/file/aa43609-22.pdf %L insu-03781617 %U https://insu.hal.science/insu-03781617 %~ INSU %~ CNRS %~ UNIV-STRASBG %~ SITE-ALSACE %~ ANR