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The double red clump (RC) observed in color-magnitude diagrams of the MilkyWay bulge is at the heart of the current debate on the structure and formationorigin of the bulge. This feature can be explained by the difference betweenthe two RCs either in distance ("X-shaped scenario") or in chemical composition("multiple-population scenario"). Here we report our high-resolutionspectroscopy for the RC and red giant branch stars in a high-latitude field (b~ -8.5$\deg$) of the bulge. We find a difference in [Fe/H] between the stars inthe bright and faint RC regimes, in the sense that the bright stars areenhanced in [Fe/H] with respect to the faint stars by 0.149 $\pm$ 0.036 dex.The stars on the bright RC are also enhanced in [Na/Fe] but appear to bedepleted in [Al/Fe] and [O/Fe], although more observations are required toconfirm the significance of these differences. Interestingly, these chemicalpatterns are similar to those observed among multiple stellar populations inthe metal-rich bulge globular cluster Terzan 5. In addition, we find a numberof Na-rich stars, which would corroborate the presence of multiple populationsin the bulge. Our results support an origin of the double RC from dissolvedglobular clusters that harbor multiple stellar populations. Thus, our studysuggests that a substantial fraction of the outer bulge stars would haveoriginated from the assembly of such stellar systems in the early phase of theMilky Way formation.

Difference in chemical composition between the bright and faint red clump stars in the Milky Way bulge