Metal-poor stars in the Galactic halo often show strong enhancements in carbon and/or neutron-capture elements .
However , the Galactic bulge is notable for its paucity of these carbon-enhanced metal-poor ( CEMP ) and/or CH-stars , with only two such objects known to date .
This begs the question whether the processes that produced their abundance distribution were governed by a comparable nucleosynthesis in similar stellar sites as for their more numerous counterparts in the halo .
Recently , two contenders of these classes of stars were discovered in the bulge , at [ Fe/H ] = -1.5 and - 2.5 dex , both of which show enhancements in [ C/Fe ] of 0.4 and 1.4 dex ( respectively ) , [ Ba/Fe ] in excess of 1.3 dex , and also elevated nitrogen .
The more metal-poor of the stars can be well matched by standard s -process nucleosynthesis in low-mass Asymptotic Giant Branch ( AGB ) polluters .
The other star shows an abnormally high [ Rb/Fe ] ratio .
Here , we further investigate the origin of the abundance peculiarities in the Rb-rich star by new , detailed measurements of heavy element abundances and by comparing the chemical element ratios of 36 species to several models of neutron-capture nucleosynthesis .
The i -process with intermediate neutron densities between those of the slow ( s - ) and rapid ( r ) -neutron-capture processes has been previously found to provide good matches of CEMP stars with enhancements in both r - and s -process elements ( class CEMP- r / s ) , rather than invoking a superposition of yields from the respective individual processes .
However , the peculiar bulge star is incompatible with a pure i -process from a single ingestion event .
Instead , it can , statistically , be better reproduced by more convoluted models accounting for two proton ingestion events , or by an i -process component in combination with s -process nucleosynthesis in low-to-intermediate mass ( 2–3 M _ { \odot } ) AGB stars , indicating multiple polluters .
Finally , we discuss the impact of mixing during stellar evolution on the observed abundance peculiarities .