The R-Process Alliance: First Release from the Northern Search for
  r-Process Enhanced Metal-Poor Stars in the Galactic Halo
  This paper presents the detailed abundances and r-process classifications of
126 newly identified metal-poor stars as part of an ongoing collaboration, the
R-Process Alliance. The stars were identified as metal-poor candidates from the
RAdial Velocity Experiment (RAVE) and were followed-up at high spectral
resolution (R~31,500) with the 3.5~m telescope at Apache Point Observatory. The
atmospheric parameters were determined spectroscopically from Fe I lines,
taking into account <3D> non-LTE corrections and using differential abundances
with respect to a set of standards. Of the 126 new stars, 124 have [Fe/H]<-1.5,
105 have [Fe/H]<-2.0, and 4 have [Fe/H]<-3.0. Nine new carbon-enhanced
metal-poor stars have been discovered, 3 of which are enhanced in r-process
elements. Abundances of neutron-capture elements reveal 60 new r-I stars (with
+0.3<=[Eu/Fe]<=+1.0 and [Ba/Eu]<0) and 4 new r-II stars (with [Eu/Fe]>+1.0).
Nineteen stars are found to exhibit a `limited-r' signature ([Sr/Ba]>+0.5,
[Ba/Eu]<0). For the r-II stars, the second- and third-peak main r-process
patterns are consistent with the r-process signature in other metal-poor stars
and the Sun. The abundances of the light, alpha, and Fe-peak elements match
those of typical Milky Way halo stars, except for one r-I star which has high
Na and low Mg, characteristic of globular cluster stars. Parallaxes and proper
motions from the second Gaia data release yield UVW space velocities for these
stars which are consistent with membership in the Milky Way halo. Intriguingly,
all r-II and the majority of r-I stars have retrograde orbits, which may
indicate an accretion origin.
