  We present a detailed chemical-abundance analysis of a highly $r$-process
enhanced (RPE) star, 2MASS J00512646-1053170, using high-resolution
spectroscopic observations with $Hubble\ Space\ Telescope$/STIS in the UV and
Magellan/MIKE in the optical. We determined abundances for 41 elements in
total, including 23 $r$-process elements and rarely probed species such as Al
II, Ge I, Mo II, Cd I, Os II, Pt I, and Au I. We find that [Ge/Fe] $= +0.10$,
which is an unusually high Ge enhancement for such a metal-poor star and
indicates contribution from a production mechanism decoupled from that of Fe.
We also find that this star has the highest Cd abundance observed for a
metal-poor star to date. We find that the dispersion in the Cd abundances of
metal-poor stars can be explained by the correlation of Cd I abundances with
the stellar parameters of the stars, indicating the presence of NLTE effects.
We also report that this star is now only the 6th star with Au abundance
determined. This result, along with abundances of Pt and Os, uphold the case
for the extension of the universal $r$-process pattern to the third $r$-process
peak and to Au. This study adds to the sparse but growing number of RPE stars
with extensive chemical-abundance inventories and highlights the need for not
only more abundance determinations of these rarely probed species, but also
advances in theoretical NLTE and astrophysical studies to reliably understand
the origin of $r$-process elements.
