The $R$-Process Alliance: Fourth Data Release from the Search for
  $r$-Process-Enhanced Stars in the Galactic Halo
  This compilation is the fourth data release from the $R$-Process Alliance
(RPA) search for $r$-process-enhanced stars, and the second release based on
"snapshot" high-resolution ($R \sim 30,000$) spectra collected with the du Pont
2.5m Telescope. In this data release, we propose a new delineation between the
$r$-I and $r$-II stellar classes at $\mathrm{[Eu/Fe]} = +0.7$, instead of the
empirically chosen $\mathrm{[Eu/Fe]} = +1.0$ level previously in use, based on
statistical tests of the complete set of RPA data released to date. We also
statistically justify the minimum level of [Eu/Fe] for definition of the $r$-I
stars, [Eu/Fe] $> +0.3$. Redefining the separation between $r$-I and $r$-II
stars will aid in analysis of the possible progenitors of these two classes of
stars and whether these signatures arise from separate astrophysical sources at
all. Applying this redefinition to previous RPA data, the number of identified
$r$-II and $r$-I stars changes to 51 and 121, respectively, from the initial
set of data releases published thus far. In this data release, we identify 21
new $r$-II, 111 new $r$-I (plus three re-identified), and 7 new (plus one
re-identified) limited-$r$ stars out of a total of 232 target stars, resulting
in a total sample of 72 new $r$-II stars, 232 new $r$-I stars, and 42 new
limited-$r$ stars identified by the RPA to date.
