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] < -1.0$) than previously reported. Our study focuses on $\alpha$ (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 $\rm[\alpha/Fe]$ for increasing metallicity up to
$\rm[Fe/H] \sim -1.0$. Moreover, stars of HStr show a median value of $+$0.5
dex for $\rm[Eu/Fe]$ with a small dispersion ($\pm$0.1 dex). Every star
analyzed with $\rm[Fe/H] < -1.2$ belong to the $r$-process enhanced
($\rm[Eu/Fe] > +0.3$ 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.
