A photometric study of globular clusters observed by the APOGEE survey

Mészáros, Szabolcs; García-Hernández, D. A.; Cassisi, S.; Monelli, M.; Szigeti, László; Dell’Agli, F.; Derekas, A.; Masseron, T.; Shetrone, Matthew; Stetson, P. B.; Zamora, Olga

doi:10.1093/mnras/stx3275

Cited by 12 publications

(31 citation statements)

References 71 publications

(94 reference statements)

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“…1g. Figure 1g indicates that [Ce/Fe] is slightly more enhanced than in NRSs, GCs, or MW stars, but agrees with GC stars (Mészáros et al 2020) at similar metallicities. However, there is currently no explanation for this unexpected tendency.…”

Section: The S-process Element: Cesupporting

confidence: 63%

“…These stars exhibit Al abundances well above typical Galactic levels ([Al/Fe] +0.5) over a range of metallicities, and resemble those known for a long time to exist in Galactic GCs (see, e.g. Mészáros et al 2020). However, they are unlikely to be linked to the accretion of dwarf galaxies, for which larger Al abundance ratios have not been observed to date (Hasselquist et al 2019, and references therein).…”

Section: Introductionmentioning

confidence: 65%

“…Overall, Fig. 1h displays the chemical-abundance pattern of GC stars from ω Cen (Mészáros et al 2020); this GC spans as wide a metallicity range as our observed Al-rich stars. The star-to-star scatter of the Al-rich stars for almost all the chemical species is similar to that typically found in ω Cen stars.…”

Section: The Odd-z Elements: Almentioning

confidence: 79%

“…[Fe/H] > −2, allows for the inclusion of metal-poor stars with high-quality spectra with reliable parameters and chemical abundances, while requiring stars with metallicity below [Fe/H] = −0.7 minimises the presence of disc stars; (ii) stars with S /N > 60 were selected to ensure that we are selecting spectra that have wellknown uncertainties in their stellar parameters and chemical abundances, and to remove stars with lower quality spectra; (iii) 3200 K < T eff < 5500 K, this temperature range ensures that stellar parameters are reliably and consistently determined, and maximises the overall quality of the abundances considered; (iv) the estimated surface gravity (log g) must be less than 3.6, to ensure inclusion of giant and subgiant stars, which have more accurate ASPCAP parameters than the dwarf stars with log g > 3.6 (due to the lack of asteroseismic surface gravities for dwarfs, only stars with log g < 3.6 have calibrated surface gravities); (v) ASPCAPFLAG == 0; this cut ensures that there are no major flagged issues, i.e. low signal-to-noise ratio, poor synthetic spectral fit, stellar parameters near grid boundaries, among others; and (vi) stars belonging to Galactic GCs from Mészáros et al (2020), anomalous stars from Martell et al (2016), Schiavon et al (2017), and Fernández-Trincado et al (2016, 2019a, and stars with carbon abundances [C/Fe] +0.15 (to ensure the low carbon abundances typical of GC stars) were excluded from the sample.…”

Section: Discussionmentioning

confidence: 99%

“…The remaining stars in our sample are located within ∼13 kpc from the Galactic centre. The light elements (C, N), the α elements (O, Mg, Si), the odd-Z element (Al), the iron-peak element (Fe), and the s-process element (Ce) of these stars are compared to those for GC stars from Mészáros et al (2020), and the local MW disc, halo, and bulge population from APOGEE DR16 (Ahumada et al 2020). Abundances were determined from a χ 2 minimisation of synthesised spectra using the BACCHUS code.…”

Section: Elemental Abundance Analysismentioning

confidence: 99%

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Aluminium-enriched metal-poor stars buried in the inner Galaxy

Fernández-Trincado

Beers

Minniti

et al. 2020

A&A

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Stars with higher levels of aluminium and nitrogen enrichment are often key pieces in the chemical makeup of multiple populations in almost all globular clusters (GCs). There is also compelling observational evidence that some Galactic components could be partially built from dissipated GCs. The identification of such stars among metal-poor field stars may therefore provide insight into the composite nature of the Milky Way (MW) bulge and inner stellar halo, and could also reveal other chemical peculiarities. Here, based on APOGEE spectra, we report the discovery of 29 mildly metal-poor ([Fe/H] ≲ −0.7) stars with stellar atmospheres strongly enriched in aluminium (Al-rich stars: [Al/Fe] ≳ +0.5), well above the typical Galactic levels, located within the solar radius toward the bulge region, which lies in highly eccentric orbits (e ≳ 0.6). We find many similarities for almost all of the chemical species measured in this work with the chemical patterns of GCs, and therefore we propose that they have likely been dynamically ejected into the bulge and inner halo from GCs formed in situ and/or GCs formed in different progenitors of known merger events experienced by the MW, such as the Gaia-Sausage-Enceladus and/or Sequoia.

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Section: The S-process Element: Cesupporting

confidence: 63%

Section: Introductionmentioning

confidence: 65%

Section: The Odd-z Elements: Almentioning

confidence: 79%

Section: Discussionmentioning

confidence: 99%

Section: Elemental Abundance Analysismentioning

confidence: 99%

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Aluminium-enriched metal-poor stars buried in the inner Galaxy

Fernández-Trincado

Beers

Minniti

et al. 2020

A&A

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H-band discovery of additional second-generation stars in the Galactic bulge globular cluster NGC 6522 as observed by APOGEE and Gaia

Fernández-Trincado

Zamora

Souto

et al. 2019

A&A

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We present elemental abundance analysis of high-resolution spectra for five giant stars, deriving Fe, Mg, Al, C, N, O, Si and Ce abundances, and spatially located within the innermost regions of the bulge globular cluster NGC 6522, based on H-band spectra taken with the multi-object APOGEE-north spectrograph from the SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. Of the five cluster candidates, two previously unremarked stars are confirmed to have second-generation (SG) abundance patterns, with the basic pattern of depletion in C and Mg simultaneous with enrichment in N and Al as seen in other SG globular cluster populations at similar metallicity. In agreement with the most recent optical studies, the NGC 6522 stars analyzed exhibit (when available) only mild overabundances of the s-process element Ce, contradicting the idea of the NGC 6522 stars being formed from gas enriched by spinstars and indicating that other stellar sources such as massive AGB stars could be the primary intracluster medium polluters. The peculiar abundance signature of SG stars have been observed in our data, confirming the presence of multiple generations of stars in NGC 6522.

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Homogeneous analysis of globular clusters from the APOGEE survey with the BACCHUS code

Masseron

García–Hernández

Mészáros

et al. 2019

A&A

158

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Aims. We aim at providing abundances of a large set of light and neutron-capture elements homogeneously analyzed and covering a wide range of metallicity to constrain globular cluster (GC) formation and evolution models. Methods. We analyze a large sample of 885 GCs giants from the APOGEE survey. We used the Cannon results to separate the red giant branch and the asymptotic giant branch stars, not only allowing for a refinement of surface gravity from isochrones, but also providing an independent H-band spectroscopic method to distinguish stellar evolutionary status in clusters. We then use the BACCHUS code to derive metallicity, microturbulence, macroturbulence and many light-element abundances as well as the neutron-capture elements Nd and Ce for the first time from the APOGEE GCs data. Results. Our independent analysis helped us to diagnose issues regarding the standard analysis of the APOGEE DR14 for lowmetallicity GC stars. Furthermore, while we confirm most of the known correlations and anti-correlation trends (Na-O, Mg-Al, C-N), we discover that some stars within our most metal-poor clusters show an extreme Mg depletion and some Si enhancement but at the same time show some relative Al depletion, displaying a turnover in the Mg-Al diagram. These stars suggest that Al has been partially depleted in their progenitors by very hot proton-capture nucleosynthetic processes. Furthermore, we attempted to quantitatively correlate the spread of Al abundances with the global properties of GCs. We find an anti-correlation of the Al spread against clusters metallicity and luminosity, but the data do not allow to find clear evidence of a dependence of N against metallicity in the more metal-poor clusters. Conclusions. Large and homogeneously analyzed samples from on-going spectroscopic surveys unveil unseen chemical details for many clusters, including a turnover in the Mg-Al anti-correlation, thus yielding new constrains for GCs formation/evolution models.

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A photometric study of globular clusters observed by the APOGEE survey

Cited by 12 publications

References 71 publications

Aluminium-enriched metal-poor stars buried in the inner Galaxy

Aluminium-enriched metal-poor stars buried in the inner Galaxy

H-band discovery of additional second-generation stars in the Galactic bulge globular cluster NGC 6522 as observed by APOGEE and Gaia

Homogeneous analysis of globular clusters from the APOGEE survey with the BACCHUS code

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