Building the Galactic halo from globular clusters: evidence from chemically unusual red giants

Martell, Sarah L.; Smolinski, J.; Beers, Timothy C.; Grebel, Eva K.

doi:10.1051/0004-6361/201117644

Cited by 162 publications

(215 citation statements)

References 83 publications

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“…The missing 90%-95% of the G1 stars had to escape, and even more had to escape if G2 stars escaped too, which is likely. These escaping stars presumably comprise the halo of the Milky Way (Prantzos & Charbonnel 2006;Martell, et al 2011), but such large halo amounts are not evident in the Fornax or WLM dwarf galaxies (Larsen et al 2012(Larsen et al , 2014Elmegreen et al 2012).…”

Section: Introductionmentioning

confidence: 99%

Globular Cluster Formation at High Density: A Model for Elemental Enrichment with Fast Recycling of Massive-star Debris

Elmegreen

2017

ApJ

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The self-enrichment of massive star clusters by p-processed elements is shown to increase significantly with increasing gas density as a result of enhanced star formation rates and stellar scatterings compared to the lifetime of a massive star. Considering the type of cloud core where a globular cluster might have formed, we follow the evolution and enrichment of the gas and the time dependence of stellar mass. A key assumption is that interactions between massive stars are important at high density, including interactions between massive stars and massive star binaries that can shred stellar envelopes. Massive-star interactions should also scatter low-mass stars out of the cluster. Reasonable agreement with the observations is obtained for a cloud core mass of ∼ 4 × 10 6 M ⊙ and a density of ∼ 2 × 10 6 cm −3 . The results depend primarily on a few dimensionless parameters, including, most importantly, the ratio of the gas consumption time to the lifetime of a massive star, which has to be low, ∼ 10%, and the efficiency of scattering low-mass stars per unit dynamical time, which has to be relatively large, such as a few percent. Also for these conditions, the velocity dispersions of embedded globular clusters should be comparable to the high gas dispersions of galaxies at that time, so that stellar ejection by multi-star interactions could cause low-mass stars to leave a dwarf galaxy host altogether. This could solve the problem of missing first-generation stars in the halos of Fornax and WLM.

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Section: Introductionmentioning

confidence: 99%

Globular Cluster Formation at High Density: A Model for Elemental Enrichment with Fast Recycling of Massive-star Debris

Elmegreen

2017

ApJ

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“…Therefore, by finding out how many field stars have light element anomalies and thus likely originated in GCs, we can study the GC-field link. The largest systematic studies undertaken so far are those by Martell & Grebel (2010) and Martell et al (2011), who focussed on C and N anomalies as traced by molecular bands in SDSS/Segue spectra. The latter study reports that 3% of field stars display the chemical characteristics of GC stars.…”

Section: Introductionmentioning

confidence: 99%

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

Lind

Koposov

Battistini

et al. 2015

A&A

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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 and find 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.

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“…At least two bursts of star formation must have occurred in GCs with the second generation being formed from a mix of pristine gas and matter enriched by nuclear processing in the massive stars of the first generation (see Gratton et al 2001). The impact of this chain of events is not limited to the history of GCs, but it probably had a key role in the building of a considerable fraction of the Galactic halo (Carretta et al 2010a;Vesperini et al 2010;Martell et al 2011). Some important links to global cluster parameters (e.g., total mass, age, and location in the Galaxy, Carretta et al 2010a) were discovered, and the ouput of extensive surveys performed with multi-object facilities, like FLAMES, (see Carretta et al 2006Carretta et al , 2009a pointed out that the characteristics of the nuclear processing occurring in early phases differ from cluster to cluster.…”

Section: Introductionmentioning

confidence: 99%

NGC 362: another globular cluster with a split red giant branch

Carretta

Bragaglia

Gratton

et al. 2013

A&A

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We obtained FLAMES GIRAFFE+UVES spectra for both first-and second-generation red giant branch (RGB) stars in the globular cluster (GC) NGC 362 and used them to derive abundances of 21 atomic species for a sample of 92 stars. The surveyed elements include proton-capture (O, Na, Mg, Al, Si), α-capture (Ca, Ti), Fe-peak (Sc, V, Mn, Co, Ni, Cu), and neutron-capture elements (Y, Zr, Ba, La, Ce, Nd, Eu, Dy). The analysis is fully consistent with that presented for twenty GCs in previous papers of this series. Stars in NGC 362 seem to be clustered into two discrete groups along the Na-O anti-correlation with a gap at [O/Na] ∼ 0 dex. Na-rich, second generation stars show a trend to be more centrally concentrated, although the level of confidence is not very high. When compared to the classical second-parameter twin NGC 288 with similar metallicity but different horizontal branch type and a much lower total mass, the proton-capture processing in stars of NGC 362 seems to be more extreme, confirming previous analysis. We discovered the presence of a secondary RGB sequence, which is redder than the bulk of the RGB. A preliminary estimate shows that this sequence comprises about 6% of RGB stars. Our spectroscopic data and literature photometry indicate that this sequence is populated almost exclusively by giants rich in Ba and is probably rich in all s-process elements, as found in other clusters. In this regard, NGC 362 joins previously studied GCs like NGC 1851, NGC 6656 (M 22), and NGC 7089 (M 2).

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Building the Galactic halo from globular clusters: evidence from chemically unusual red giants

Cited by 162 publications

References 83 publications

Globular Cluster Formation at High Density: A Model for Elemental Enrichment with Fast Recycling of Massive-star Debris

Globular Cluster Formation at High Density: A Model for Elemental Enrichment with Fast Recycling of Massive-star Debris

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

NGC 362: another globular cluster with a split red giant branch

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