Title: The Gaia-ESO Survey: low-alpha element stars in the Galactic Bulge,
Abstract: We take advantage of the Gaia-ESO Survey iDR4 bulge data to search for
abundance anomalies that could shed light on the composite nature of the Milky
Way bulge. The alpha-elements (Mg, Si, and whenever available, Ca) abundances,
and their trends with Fe abundances have been analysed for a total of 776 bulge
stars. In addition, the aluminum abundances and their ratio to Fe and Mg have
also been examined. Our analysis reveals the existence of low-alpha element
abundance stars with respect to the standard bulge sequence in the [alpha/Fe]
vs. [Fe/H] plane. 18 objects present deviations in [alpha/Fe] ranging from 2.1
to 5.3 sigma with respect to the median standard value. Those stars do not show
Mg-Al anti-correlation patterns. Incidentally, this sign of the existence of
multiple stellar populations is reported firmly for the first time for the
bulge globular cluster NGC 6522. The identified low-alpha abundance stars have
chemical patterns compatible with those of the thin disc. Their link with
massive dwarf galaxies accretion seems unlikely, as larger deviations in alpha
abundance and Al would be expected. The vision of a bulge composite nature and
a complex formation process is reinforced by our results. The used approach, a
multi-method and model-driven analysis of high resolution data seems crucial to
reveal this complexity.