Light and Heavy Element Abundance Variations in the Outer Halo Globular Cluster NGC 6229

Johnson, Christian I.; Caldwell, Nelson; Rich, R. Michael; Walker, Matthew G.

doi:10.3847/1538-3881/aa86ac

Cited by 22 publications

(14 citation statements)

References 117 publications

(197 reference statements)

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“…These results were later confirmed by Yong et al (2016), who analysed a large sample of CaT spectroscopy of this cluster and found a range of [Fe/H] values spanning ∼ 1 dex ( = 0.17). This was followed up by Johnson et al (2017) who used a large sample of high and medium resolution spectra of NGC 6273 members, and found a dispersion in [Fe/H] of ∼ 0.2 dex, with a full range of values from [Fe/H] ∼ −2 to −1 dex 1 . Additionally, they find some evidence for three discrete sub-populations in metallicity space with each sub-populations exhibiting the classic signatures of MPs.…”

Section: Ngc 6273 (M19)mentioning

confidence: 96%

“…They also identified a population of at least five peculiar "low-" stars that have [ /Fe] ∼ 0.0 and low [Na/Fe] and [Al/Fe] abundances. 1 We note that while Johnson et al (2015Johnson et al ( , 2017 used the 'spectroscopic' approach to determine the Fe spread within M 19, which can lead to an artificial broadening of the intrinsic Fe spread (e.g., Lardo et al 2016;Mucciarelli et al 2016), the large spread found in M 19 (∼ 1 dex) argues that a large and true Fe spread exists within this cluster. Future work using the "photometric" method on this cluster will be able to confirm this.…”

Section: Ngc 6273 (M19)mentioning

confidence: 98%

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The accreted nuclear clusters of the Milky Way

Pfeffer

Lardo

Bastian

et al. 2020

Monthly Notices of the Royal Astronomical Society

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A number of the massive clusters in the halo, bulge and disc of the Galaxy are not genuine globular clusters (GCs), but instead are different beasts altogether. They are the remnant nuclear star clusters (NSCs) of ancient galaxies since accreted by the Milky Way. While some clusters are readily identifiable as NSCs, and can be readily traced back to their host galaxy (e.g., M54 and the Sagittarius Dwarf galaxy) others have proven more elusive. Here we combine a number of independent constraints, focusing on their internal abundances and overall kinematics, to find NSCs accreted by the Galaxy and trace them to their accretion event. We find that the true NSCs accreted by the Galaxy are: M54 from the Sagittarius Dwarf, ω Centari from Gaia-Enceladus/Sausage, NGC 6273 from Kraken and (potentially) NGC 6934 from the Helmi Streams. These NSCs are prime candidates for searches of intermediate mass black holes (BHs) within star clusters, given the common occurrence of galaxies hosting both NSCs and central massive BHs. No NSC appears to be associated with Sequoia or other minor accretion events. Other claimed NSCs are shown not to be such. We also discuss the peculiar case of Terzan 5, which may represent a unique case of a cluster-cluster merger.

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Section: Ngc 6273 (M19)mentioning

confidence: 96%

Section: Ngc 6273 (M19)mentioning

confidence: 98%

The accreted nuclear clusters of the Milky Way

Pfeffer

Lardo

Bastian

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…In particular, clusters possessing warmer blue HB populations and larger present-day masses tend to exhibit more extreme [O/Na] and [Mg/Al] abundance ranges (Carretta et al 2007(Carretta et al , 2010a; Gratton et al 2010). A significant fraction of clusters with M V < ∼ −8 exhibit variations in Fe-peak and s-process abundances as well, and some evidence indicates that many of these "Fe-complex" or "Type II" clusters may be the remnant cores of former dwarf galaxies (e.g., Da Costa 2016;Johnson et al 2017a;Marino et al 2018). In fact, Lee et al (2007) suggests that most or all clusters with significant blue HB populations have an accretion origin.…”

Section: Introductionmentioning

confidence: 99%

“…Clusters such as M 4(Marino et al 2008;Villanova & Geisler 2011) also exhibit significant composition gaps but do not contain E stars Lapenna et al (2015),. andJohnson et al (2017aJohnson et al ( , 2018). The literature sources were shifted to have approximately the same upper [O/Fe] and lower [Na/Fe] bounds as NGC 6402, and were resampled 10 4 times.…”

mentioning

confidence: 99%

Light element discontinuities suggest an early termination of star formation in the globular cluster NGC 6402 (M14)

Johnson

Caldwell

Rich

et al. 2019

Monthly Notices of the Royal Astronomical Society

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NGC 6402 is among the most massive globular clusters in the Galaxy, but little is known about its detailed chemical composition. Therefore, we obtained radial velocities and/or chemical abundances of 11 elements for 41 red giant branch cluster members using high resolution spectra obtained with the Magellan-M2FS instrument. We find NGC 6402 to be only moderately metal-poor with [Fe/H] = −1.13 dex (σ = 0.05 dex) and to have a mean heliocentric radial velocity of −61.1 km s −1 (σ = 8.5 km s −1 ). In general, NGC 6402 exhibits mean composition properties that are similar to other inner Galaxy clusters, such as [α/Fe] ∼ +0.3 dex, [Cr,Ni/Fe] ∼ 0.0 dex, and [La/Eu] = −0.08 dex. Similarly, we find large star-to-star abundance variations for O, Na, Mg, Al, and Si that are indicative of gas that experienced high temperature proton-capture burning. Interestingly, we detect three distinct populations, but also find large gaps in the [O/Fe], [Na/Fe], and [Al/Fe] distributions that may provide the first direct evidence of delayed formation for intermediate composition stars. A qualitative enrichment model is discussed where clusters form stars through an early ( < ∼ 5−10 Myr) phase, which results in first generation and "extreme" composition stars, and a delayed phase ( > ∼ 40 Myr), which results in the dilution of processed and pristine gas and the formation of intermediate composition stars. For NGC 6402, the missing intermediate composition stars suggest the delayed phase terminated prematurely, and as a result the cluster may uniquely preserve details of the chemical enrichment process.

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“…For NGC 6569, which has E(B − V )>0.55 (see Section 4.1), a near-infrared calibration is preferred over those using V-band magnitudes (e.g., Starkenburg et al 2010;Saviane et al 2012;Carrera et al 2013) Given the moderately high resolution and S/N of our data, the internal abundance uncertainties are dominated by errors in model atmosphere parameter determinations. For T eff , we have adopted an uncertainty value of 100 K based on the log ò(Fe I) versus lower excitation potential plots, previous comparisons of spectroscopic and photometric temperatures using low reddening clusters (e.g., Johnson et al 2015aJohnson et al , 2017c, and the scatter present in a plot of J-K S versus spectroscopic temperature for the current data set. Similarly, we have adopted a conservative log(g) uncertainty of 0.15 cgs for all stars based on an examination of the scatter present when binning the data into groups spanning ∼100 K each (see also Section 4.1 and Figure 4).…”

Section: Calcium Triplet [Fe/h] Determinationsmentioning

confidence: 99%

Exploring the Chemical Composition and Double Horizontal Branch of the Bulge Globular Cluster NGC 6569

Johnson

Rich

Caldwell

et al. 2018

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Photometric and spectroscopic analyses have shown that the Galactic bulge cluster Terzan 5 hosts several populations with different metallicities and ages that manifest as a double red horizontal branch (HB). A recent investigation of the massive bulge cluster NGC 6569 revealed a similar, though less extended, HB luminosity split, but little is known about the cluster's detailed chemical composition. Therefore, we have used high-resolution spectra from the Magellan-M2FS and VLT-FLAMES spectrographs to investigate the chemical compositions and radial velocity distributions of red giant branch and HB stars in NGC 6569. We found the cluster to have a mean heliocentric radial velocity of −48.8 km s 11 dex indicates significant pollution with r-process material. We confirm that both HBs contain cluster members, but metallicity and lightelement variations are largely ruled out as sources for the luminosity difference. However, He mass fraction differences as small as ΔY∼0.02 cannot be ruled out and may be sufficient to reproduce the double HB.

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Light and Heavy Element Abundance Variations in the Outer Halo Globular Cluster NGC 6229

Cited by 22 publications

References 117 publications

The accreted nuclear clusters of the Milky Way

The accreted nuclear clusters of the Milky Way

Light element discontinuities suggest an early termination of star formation in the globular cluster NGC 6402 (M14)

Exploring the Chemical Composition and Double Horizontal Branch of the Bulge Globular Cluster NGC 6569

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