We present a detailed analysis of the composition and nucleosynthetic origins of the heavy elements in the metal-poor ( [ Fe/H ] = - 1.62 \pm 0.09 ) star HD 94028 .
Previous studies revealed that this star is mildly enhanced in elements produced by the slow neutron-capture process ( s process ; e.g. , [ Pb/Fe ] = + 0.79 \pm 0.32 ) and rapid neutron-capture process ( r process ; e.g. , [ Eu/Fe ] = + 0.22 \pm 0.12 ) , including unusually large molybdenum ( [ Mo/Fe ] = + 0.97 \pm 0.16 ) and ruthenium ( [ Ru/Fe ] = + 0.69 \pm 0.17 ) enhancements .
However , this star is not enhanced in carbon ( [ C/Fe ] = - 0.06 \pm 0.19 ) .
We analyze an archival near-ultraviolet spectrum of HD 94028 , collected using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope , and other archival optical spectra collected from ground-based telescopes .
We report abundances or upper limits derived from 64 species of 56 elements .
We compare these observations with s -process yields from low-metallicity AGB evolution and nucleosynthesis models .
No combination of s - and r -process patterns can adequately reproduce the observed abundances , including the super-solar [ As/Ge ] ratio ( + 0.99 \pm 0.23 ) and the enhanced [ Mo/Fe ] and [ Ru/Fe ] ratios .
We can fit these features when including an additional contribution from the intermediate neutron-capture process ( i process ) , which perhaps operated by the ingestion of H in He-burning convective regions in massive stars , super-AGB stars , or low-mass AGB stars .
Currently , only the i process appears capable of consistently producing the super-solar [ As/Ge ] ratios and ratios among neighboring heavy elements found in HD 94028 .
Other metal-poor stars also show enhanced [ As/Ge ] ratios , hinting that operation of the i process may have been common in the early Galaxy .