The<i>Gaia</i>-ESO Survey: A globular cluster escapee in the Galactic halo

Lind, Karin; Koposov, S. E.; Battistini, C.; Marino, A. F.; Ruchti, G.; Serenelli, Aldo; Worley, C. C.; Alves-Brito, Alan; Asplund, Martin; Barklem, P. S.; Bensby, T.; Bergemann, M.; Blanco-Cuaresma, S.; Bragaglia, A.; Edvardsson, B.; Feltzing, Sofia; Gruyters, Pieter; Heiter, U.; Jofré, P.; Korn, A. J.; Nordlander, Thomas; Ryde, Nils; Soubiran, C.; Gilmore, G.; Randich, S.; Ferguson, Annette M. N.; Jeffries, R. D.; Vallenari, A.; Prieto, C. Allende; Pancino, E.; Recio–Blanco, A.; Romano, D.; Smiljanić, R.; Bellazzini, M.; Damiani, F.; Hill, V.; Laverny, P. de; Jackson, R. J.; Lardo, C.; Zaggia, S.

doi:10.1051/0004-6361/201425554

Cited by 54 publications

(56 citation statements)

References 50 publications

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“…Previous work has indeed suggested the presence of a possible gradient in the incidence of N-rich stars (Carollo et al 2013) in the Galactic halo. Considering also the fact that stars with second generation abundances have been found in the halo (e.g., Martell et al 2011;Carretta et al 2010;Carollo et al 2013;Lind et al 2015;Fernandez-Trincado et al 2016), it seems natural to conclude that an association of our N-rich population to the inner halo seems more likely than to the thick disk. The discrepancy with the numbers expected in other regions of the halo (e.g., Martell et al 2011Martell et al , 2016 indicates that the frequency of N-rich stars may be higher in the inner halo, which is in and of itself an important constraint on models for the origin of this population.…”

Section: Bulge Thick Disk or Halo?mentioning

confidence: 97%

Chemical tagging with APOGEE: discovery of a large population of N-rich stars in the inner Galaxy

Schiavon

Zamora

Carrera

et al. 2016

Mon. Not. R. Astron. Soc.

186

157

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Formation of globular clusters (GCs), the Galactic bulge, or galaxy bulges in general, are important unsolved problems in Galactic astronomy. Homogeneous infrared observations of large samples of stars belonging to GCs and the Galactic bulge field are one of the best ways to study these problems. We report the discovery by APOGEE of a population of field stars in the inner Galaxy with abundances of N, C, and Al that are typically found in GC stars. The newly discovered stars have high [N/Fe], which is correlated with [Al/Fe] and anti-correlated with [C/Fe]. They are homogeneously distributed across, and kinematically indistinguishable from, other field stars in the same volume. Their metallicity distribution is seemingly unimodal, peaking at [Fe/H]∼-1, thus being in disagreement with that of the Galactic GC system. Our results can be understood in terms of different scenarios. N-rich stars could be former members of dissolved GCs, in which case the mass in destroyed GCs exceeds that of the surviving GC system by a factor of ∼8. In that scenario, the total mass contained in so-called "first-generation" stars cannot be larger than that in "second-generation" stars by more than a factor of ∼9 and was certainly smaller. Conversely, our results may imply the absence of a mandatory genetic link between "second generation" stars and GCs. Last, but not least, N-rich stars could be the oldest stars in the Galaxy, the by-products of chemical enrichment by the first stellar generations formed in the heart of the Galaxy.

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Section: Bulge Thick Disk or Halo?mentioning

confidence: 97%

Chemical tagging with APOGEE: discovery of a large population of N-rich stars in the inner Galaxy

Schiavon

Zamora

Carrera

et al. 2016

Mon. Not. R. Astron. Soc.

186

157

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“…A small number of studies have done exactly this, searching large collections of spectroscopic data for field stars that follow the globular cluster abundance pattern. Martell & Grebel (2010) and Martell et al (2011) used the Sloan Digital Sky Survey (SDSS)-II/SEGUE (Yanny et al 2009) and SDSS-III/SEGUE-2 (Eisenstein et al 2011) surveys, respectively, as their data sources, while Carretta et al (2010a) and Ramírez et al (2012) used literature compilations originally assembled for other purposes, and Lind et al (2015) used the Gaia-ESO Survey (Gilmore et al 2012). Due to differences in the data available to the various authors, a number of different chemical tags have been used to identify these migrant stars, but all involve some part of the characteristic globular cluster abundance pattern.…”

Section: Chemical Tagging Of Migrant Field Starsmentioning

confidence: 99%

Chemical Tagging in the SDSS-Iii/Apogee Survey: New Identifications of Halo Stars With Globular Cluster Origins

Martell

Shetrone²,

Lucatello

et al. 2016

ApJ

104

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We present new identifications of five red giant stars in the Galactic halo with chemical abundance patterns that indicate they originally formed in globular clusters. Using data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) Survey available through Sloan Digital Sky Survey (SDSS) Data Release 12, we first identify likely halo giants, and then search those for the well-known chemical tags associated with globular clusters, specifically enrichment in nitrogen and aluminum. We find that 2% of the halo giants in our sample have this chemical signature, in agreement with previous results. Following the interpretation in our previous work on this topic, this would imply that at least 13% of halo stars originally formed in globular clusters. Recent developments in the theoretical understanding of globular cluster formation raise questions about that interpretation, and we concede the possibility that these migrants represent a small fraction of the halo field. There are roughly as many stars with the chemical tags of globular clusters in the halo field as there are in globular clusters, whether or not they are accompanied by a much larger chemically untaggable population of former globular cluster stars.

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“…Lind et al (2015) argue that stars with low [Mg/Fe] ratios are commonly found in dSph galaxies. However, [Al/Fe] enhancement is not expected in these systems (see Koch & McWilliam 2008).…”

Section: Possible Originsmentioning

confidence: 99%

Discovery of a Metal-Poor Field Giant With a Globular Cluster Second-Generation Abundance Pattern

Fernández-Trincado

Robin

Moreno

et al. 2016

ApJ

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We report on the detection, from observations obtained with the Apache Point Observatory Galactic Evolution Experiment spectroscopic survey, of a metal-poor ([Fe/H]=−1.3 dex) field giant star with an extreme Mg-Al abundance ratio ([Mg/Fe]=−0.31 dex; [Al/Fe]=1.49 dex). Such low Mg/Al ratios are seen only among the second-generation population of globular clusters (GCs) and are not present among Galactic disk field stars. The light-element abundances of this star, 2M16011638-1201525, suggest that it could have been born in a GC. We explore several origin scenarios, studying the orbit of the star in particular to check the probability of its being kinematically related to known GCs. We performed simple orbital integrations assuming the estimated distance of 2M16011638-1201525 and the available six-dimensional phase-space coordinates of 63 GCs, looking for close encounters in the past with a minimum distance approach within the tidal radius of each cluster. We found a very low probability that 2M16011638-1201525 was ejected from most GCs; however, we note that the best progenitor candidate to host this star is GC ω Centauri (NGC 5139). Our dynamical investigation demonstrates that 2M16011638-1201525 reaches a distance < Z 3 kpc max | | from the Galactic plane and minimum and maximum approaches to the Galactic center of R min <0.62 kpc and R max <7.26 kpc in an eccentric (e ∼ 0.53) and retrograde orbit. Since the extreme chemical anomaly of 2M16011638-1201525 has also been observed in halo field stars, this object could also be considered a halo contaminant, likely to have been ejected into the Milky Way disk from the halo. We conclude that 2M16011638-20152 is also kinematically consistent with the disk but chemically consistent with halo field stars.

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

Cited by 54 publications

References 50 publications

Chemical tagging with APOGEE: discovery of a large population of N-rich stars in the inner Galaxy

Chemical tagging with APOGEE: discovery of a large population of N-rich stars in the inner Galaxy

Chemical Tagging in the SDSS-Iii/Apogee Survey: New Identifications of Halo Stars With Globular Cluster Origins

Discovery of a Metal-Poor Field Giant With a Globular Cluster Second-Generation Abundance Pattern

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