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The Gaia-ESO Survey: A globular cluster escapee in the Galactic halo

Lind, K and Koposov, SE and Battistini, C and Marino, AF and Ruchti, G and Serenelli, A and Worley, CC and Alves-Brito, A and Asplund, M and Barklem, PS and Bensby, T and Bergemann, M and Blanco-Cuaresma, S and Bragaglia, A and Edvardsson, B and Feltzing, S and Gruyters, P and Heiter, U and Jofre, P and Korn, AJ and Nordlander, T and Ryde, N and Soubiran, C and Gilmore, G and Randich, S and Ferguson, AMN and Jeffries, RD and Vallenari, A and Allende Prieto, C and Pancino, E and Recio-Blanco, A and Romano, D and Smiljanic, R and Bellazzini, M and Damiani, F and Hill, V and de laverny, P and Jackson, RJ and Lardo, C and Zaggia, S (2015) The Gaia-ESO Survey: A globular cluster escapee in the Galactic halo. Astronomy & Astrophysics, 575. ISSN 1432-0746

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Abstract

A small fraction of the halo field is made up of stars that share the light element (Z ≤ 13) anomalies characteristic of second generation globular cluster (GC) stars. The ejected stars shed light on the formation of the Galactic halo by tracing the dynamical history of the clusters, which are believed to have once been more massive. Some of these ejected stars are expected to show strong Al enhancement at the expense of shortage of Mg, but until now no such star has been found. We search for outliers in the Mg and Al abundances of the few hundreds of halo field stars observed in the first eighteen months of the Gaia-ESO public spectroscopic survey. One halo star at the base of the red giant branch, here referred to as 22593757-4648029 is found to have [ Mg/Fe ] = −0.36 ± 0.04 and [ Al/Fe ] = 0.99 ± 0.08, which is compatible with the most extreme ratios detected in GCs so far. We compare the orbit of 22593757-4648029 to GCs of similar metallicity andfind it unlikely that this star has been tidally stripped with low ejection velocity from any of the clusters. However, both chemical and kinematic arguments render it plausible that the star has been ejected at high velocity from the anomalous GC ω Centauri within the last few billion years. We cannot rule out other progenitor GCs, because some may have disrupted fully, and the abundance and orbital data are inadequate for many of those that are still intact.

Item Type: Article
Uncontrolled Keywords: 0201 Astronomical And Space Sciences
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: EDP Sciences
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Date Deposited: 23 Nov 2016 11:37
Last Modified: 23 Nov 2016 11:37
DOI or Identification number: 10.1051/0004-6361/201425554
URI: http://researchonline.ljmu.ac.uk/id/eprint/4847

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