Volume 602, June 2017
|Number of page(s)||6|
|Published online||27 June 2017|
The Gaia-ESO Survey: Low-α element stars in the Galactic bulge⋆
1 Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, 06300 Laboratoire Lagrange, France
2 Institute of Theoretical Physics and Astronomy, Vilnius University, A. Goštauto 12, 01108 Vilnius, Lithuania
3 Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Santiago, Chile
4 Millennium Institute of Astrophysics, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, Chile
5 Institut Utinam, CNRS, Université de Franche-Comté, OSU THETA Franche-Comté-Bourgogne, Obs. de Besançon, 25000 Besançon, France
6 GEPI, Observatoire de Paris, CNRS, Université Paris Diderot, 5 Place Jules Janssen, 92190 Meudon, France
7 Institute of Astronomy, Cambridge University, Madingley Road, Cambridge CB3 0HA, UK
8 INAF–Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 5, 50125 Firenze, Italy
9 Instituto de Astrofísica de Andalucía-CSIC, Apdo. 3004, 18080 Granada, Spain
10 Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
11 INAF−Osservatorio Astronomico di Bologna, via Ranzani 1, 40127, Bologna, Italy
12 Dip. di Fisica e Astronomia, Univ. de Padova, Vicolo Osservatorio 3, 35122 Padova, Italy
13 Núcleo de Astronomía, Facultad de Ingeniería, Universidad Diego Portales, Av. Ejercito 441, Santiago, Chile
14 Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK
15 Departamento de Ciencias Fisicas, Universidad Andres Bello, Republica 220, Santiago, Chile
16 INAF–Padova Observatory, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
Received: 8 December 2016
Accepted: 14 February 2017
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.
Key words: Galaxy: bulge / Galaxy: abundances / Galaxy: stellar content
Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 188.B-3002. These data products have been processed by the Cambridge Astronomy Survey Unit (CASU) at the Institute of Astronomy, University of Cambridge, and by the FLAMES/UVES reduction team at INAF/Osservatorio Astrofisico di Arcetri. These data have been obtained from the Gaia-ESO Survey Data Archive, and prepared and hosted by the Wide Field Astronomy Unit, Institute for Astronomy, University of Edinburgh, which is funded by the UK Science and Technology Facilities Council.
© ESO, 2017
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