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 α-element (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-α element abundance stars with respect to the standard bulge sequence in the [α/ Fe] versus [Fe/H] plane. Eighteen objects present deviations in [α/ Fe] ranging from 2.1 to 5.3σ 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-α abundance stars have chemical patterns that are compatible with those of the thin disc. Their link with massive dwarf galaxies accretion seems unlikely, as larger deviations in α abundance and Al would be expected. The vision of a bulge composite nature and a complex formation process is reinforced by our results. The approach used, which is a multi-method and model-driven analysis of high resolution data, seems crucial to reveal this complexity.
Recio-Blanco A., Rojas-Arriagada A., De Laverny P., Mikolaitis S., Hill V., Zoccali M., et al. (2017). The Gaia-ESO Survey: Low-α element stars in the Galactic bulge. ASTRONOMY & ASTROPHYSICS, 602, L14-L14 [10.1051/0004-6361/201630220].
The Gaia-ESO Survey: Low-α element stars in the Galactic bulge
Lardo C.;
2017
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 α-element (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-α element abundance stars with respect to the standard bulge sequence in the [α/ Fe] versus [Fe/H] plane. Eighteen objects present deviations in [α/ Fe] ranging from 2.1 to 5.3σ 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-α abundance stars have chemical patterns that are compatible with those of the thin disc. Their link with massive dwarf galaxies accretion seems unlikely, as larger deviations in α abundance and Al would be expected. The vision of a bulge composite nature and a complex formation process is reinforced by our results. The approach used, which is a multi-method and model-driven analysis of high resolution data, seems crucial to reveal this complexity.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
