We present a detailed abundance analysis of the bright ( V = 9.02 ) , metal-poor ( [ Fe/H ] = - 1.47 \pm 0.08 ) field red horizontal-branch star HD 222925 , which was observed as part of an ongoing survey by the R -Process Alliance .
We calculate stellar parameters and derive abundances for 46 elements based on 901 lines examined in a high-resolution optical spectrum obtained using the Magellan Inamori Kyocera Echelle spectrograph .
We detect 28 elements with 38 \leq Z \leq 90 ; their abundance pattern is a close match to the Solar r -process component .
The distinguishing characteristic of HD 222925 is an extreme enhancement of r -process elements ( [ Eu/Fe ] = + 1.33 \pm 0.08 , [ Ba/Eu ] = - 0.78 \pm 0.10 ) in a moderately metal-poor star , so the abundance of r -process elements is the highest ( [ Eu/H ] = - 0.14 \pm 0.09 ) in any known r -process-enhanced star .
The abundance ratios among lighter ( Z \leq 30 ) elements are typical for metal-poor stars , indicating that production of these elements was dominated by normal Type II supernovae , with no discernible contributions from Type Ia supernovae or asymptotic giant branch stars .
The chemical and kinematic properties of HD 222925 suggest it formed in a low-mass dwarf galaxy , which was enriched by a high-yield r -process event before being disrupted by interaction with the Milky Way .