Abundance Patterns of $\alpha$ and Neutron-capture Elements in the Helmi Stream.

We identified 8 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 $\sim$0.5 dex) metallicity interval ($-2.5 \lesssim \rm[Fe/H] +0.3$ and $\rm[Ba/Eu] < 0.0$) metal-poor category, providing remarkable evidence that, at such 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 $\rm[Ba/Eu]$ for higher $\rm[Fe/H]$, in conformity with other surviving dwarf satellite galaxies of the Milky Way.