# The Gaia-ESO Survey: low-alpha element stars in the Galactic Bulge

## TL;DR

This study analyzes Gaia-ESO Survey data to identify low-alpha element stars in the Galactic Bulge, revealing a complex, composite formation history with evidence of multiple stellar populations.

## Contribution

It reports the first detection of low-alpha stars in the bulge and links their chemical patterns to the thin disc, highlighting bulge complexity.

## Key findings

- Identification of 18 low-alpha stars deviating from the bulge sequence.
- Low-alpha stars show chemical patterns similar to the thin disc.
- Evidence supporting a complex, multi-component bulge formation process.

## 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.