The R-Process Alliance: A Nearly Complete R-Process Abundance Template
  Derived from Ultraviolet Spectroscopy of the R-Process-Enhanced Metal-Poor
  Star HD 222925
  We present a nearly complete rapid neutron-capture process (r-process)
chemical inventory of the metal-poor ([Fe/H] = -1.46 +/- 0.10)
r-process-enhanced ([Eu/Fe] = +1.32 +/- 0.08) halo star HD 222925. This
abundance set is the most complete for any object beyond the solar system,
totaling 63 metals detected and 7 with upper limits. It comprises 42 elements
from 31 <= Z <= 90, including elements rarely detected in r-process-enhanced
stars, such as Ga, Ge, As, Se, Cd, In, Sn, Sb, Te, W, Re, Os, Ir, Pt, and Au.
We derive these abundances from an analysis of 404 absorption lines in
ultraviolet spectra collected using the Space Telescope Imaging Spectrograph on
the Hubble Space Telescope and previously analyzed optical spectra. A series of
appendices discusses the atomic data and quality of fits for these lines. The
r-process elements from Ba to Pb, including all elements at the third r-process
peak, exhibit remarkable agreement with the Solar r-process residuals, with a
standard deviation of the differences of only 0.08 dex (17%). In contrast,
deviations among the lighter elements from Ga to Te span nearly 1.4 dex, and
they show distinct trends from Ga to Se, Nb through Cd, and In through Te. The
r-process contribution to Ga, Ge, and As is small, and Se is the lightest
element whose production is dominated by the r-process. The lanthanide
fraction, log(X_La) = -1.40 +/- 0.09, is typical for r-process-enhanced stars
and higher than that of the kilonova from the GW170817 neutron-star merger
event. We advocate adopting this pattern as an alternative to the Solar
r-process-element residuals when confronting future theoretical models of
heavy-element nucleosynthesis with observations.
