The r-Process Pattern of a Bright, Highly r-Process-Enhanced, Metal-Poor
  Halo Star at [Fe/H] ~ -2
  A high-resolution spectroscopic analysis is presented for a new highly
r-process-enhanced ([Eu/Fe] = 1.27, [Ba/Eu] = -0.65), very metal-poor ([Fe/H] =
-2.09), retrograde halo star, RAVE J153830.9-180424, discovered as part of the
R-Process Alliance survey. At V = 10.86, this is the brightest and most
metal-rich r-II star known in the Milky Way halo. Its brightness enables
high-S/N detections of a wide variety of chemical species that are mostly
created by the r-process, including some infrequently detected lines from
elements like Ru, Pd, Ag, Tm, Yb, Lu, Hf, and Th, with upper limits on Pb and
U. This is the most complete r-process census in a very metal-poor r-II star.
J1538-1804 shows no signs of s-process contamination, based on its low [Ba/Eu]
and [Pb/Fe]. As with many other r-process-enhanced stars, J1538-1804's
r-process pattern matches that of the Sun for elements between the first,
second, and third peaks, and does not exhibit an actinide boost.
Cosmo-chronometric age-dating reveals the r-process material to be quite old.
This robust main r-process pattern is a necessary constraint for r-process
formation scenarios (of particular interest in light of the recent neutron star
merger, GW 170817), and has important consequences for the origins of r-II
stars. Additional r-I and r-II stars will be reported by the R-Process Alliance
in the near future.
