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1. CAPOS: the bulge Cluster APOgee Survey IV elemental abundances of the bulge globular cluster NGC 6558

   https://doi.org/10.1093/mnras/stad3178  

   González-Díaz, Danilo; Fernández-Trincado, José G.; Villanova, Sandro; Geisler, Doug; Barbuy, Beatriz; Minniti, Dante; Beers, Timothy C.; Moni Bidin, Christian; Mauro, Francesco; Muñoz, Cesar; et al (October 2023, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT This study presents the results concerning six red giant stars members of the globular cluster NGC 6558. Our analysis utilized high-resolution near-infrared spectra obtained through the CAPOS initiative (the APOgee Survey of Clusters in the Galactic Bulge), which focuses on surveying clusters within the Galactic Bulge, as a component of the Apache Point Observatory Galactic Evolution Experiment II survey (APOGEE-2). We employ the Brussels Automatic Code for Characterizing High accUracy Spectra (BACCHUS) code to provide line-by-line elemental-abundances for Fe-peak (Fe, Ni), α-(O, Mg, Si, Ca, Ti), light-(C, N), odd-Z (Al), and the s-process element (Ce) for the four stars with high-signal-to-noise ratios. This is the first reliable measure of the CNO abundances for NGC 6558. Our analysis yields a mean metallicity for NGC 6558 of 〈[Fe/H]〉 = −1.15 ± 0.08, with no evidence for a metallicity spread. We find a Solar Ni abundance, 〈[Ni/Fe]〉 ∼ +0.01, and a moderate enhancement of α-elements, ranging between +0.16 and <+0.42, and a slight enhancement of the s-process element 〈[Ce/Fe]〉 ∼ +0.19. We also found low levels of 〈[Al/Fe]〉 ∼ +0.09, but with a strong enrichment of nitrogen, [N/Fe] > +0.99, along with a low level of carbon, [C/Fe] < −0.12. This behaviour of Nitrogen-Carbon is a typical chemical signature for the presence of multiple stellar populations in virtually all GCs; this is the first time that it is reported in NGC 6558. We also observed a remarkable consistency in the behaviour of all the chemical species compared to the other CAPOS bulge GCs of the same metallicity. 

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2. The Open Cluster Chemical Abundances and Mapping Survey. IV. Abundances for 128 Open Clusters Using SDSS/APOGEE DR16

   https://doi.org/10.3847/1538-3881/ab77bc  

   Donor, John; Frinchaboy, Peter M.; Cunha, Katia; O’Connell, Julia E.; Prieto, Carlos Allende; Almeida, Andrés; Anders, Friedrich; Beaton, Rachael; Bizyaev, Dmitry; Brownstein, Joel R.; et al (May 2020, The Astronomical Journal)
3. The Open Cluster Chemical Abundances and Mapping Survey. V. Chemical Abundances of CTIO/Hydra Clusters Using The Cannon

   https://doi.org/10.3847/1538-3881/ac5835  

   Ray, Amy E.; Frinchaboy, Peter M.; Donor, John; Chojnowski, S. D.; Melendez, Matthew (April 2022, The Astronomical Journal)

   Abstract Open clusters are key chemical and age tracers of Milky Way evolution. While open clusters provide significant constraints on galaxy evolution, their use has been limited due to discrepancies in measuring abundances from different studies. We analyze medium-resolution (R∼ 19,000) Cerro Tololo Inter-American Observatory/Hydra spectra of giant stars in 58 open clusters using The Cannon to determine [Fe/H], [Mg/Fe], [Si/Fe], [Al/Fe], and [O/Fe]. This work adds an additional 55 primarily southern hemisphere open clusters calibrated to the Sloan Digital Sky Survey/Apache Point Observatory Galactic Evolution Experiment DR16 metallicity system. This uniform analysis is compared to previous studies [Fe/H] measurements for 23 clusters and we present spectroscopic metallicities for the first time for 35 open clusters. 

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4. Cosmological constraints from DES Y1 cluster abundances and SPT multiwavelength data

   https://doi.org/10.1103/PhysRevD.103.043522  

   Costanzi, M.; Saro, A.; Bocquet, S.; Abbott, T. M. C.; Aguena, M.; Allam, S.; Amara, A.; Annis, J.; Avila, S.; Bacon, D.; et al (February 2021, Physical Review D)

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5. Chemical Abundances in the Metal-Poor Globular Cluster ESO 280-SC06: A Formerly Massive, Tidally Disrupted Globular Cluster

   https://doi.org/10.33232/001c.141756  

   Usman, Sam A; Ji, Alexander P; Rodriguez, Jandrie; Simpson, Jeffrey D; Martell, Sarah L; Li, Ting S; Bonaca, Ana; Shah, Shivani; McKenzie, Madeleine (January 2025, The Open Journal of Astrophysics)

   We present the first high-resolution abundance study of ESO 280-SC06, one of the least luminous and most metal-poor gravitationally bound Milky Way globular clusters. Using Magellan/MIKE spectroscopy for ten stars, we confirm the cluster’s low metallicity as [Fe/H] = $-2.54\pm 0.06$and the presence of a nitrogen-enhanced star enriched by binary mass transfer. We determine abundances or abundance upper limits for 21 additional elements from the light, alpha, odd-Z, iron peak, and neutron-capture groups for all ten stars. We find no spread in neutron-capture elements, unlike previous trends identified in some metal-poor globular clusters such as M15 and M92. Eight of the ten stars have light-element abundance patterns consistent with second-population globular cluster stars, which is a significantly larger second-population fraction than would be expected from the low present-day mass of ${10}^{4.1}$Msun. We estimate the initial mass of the cluster as ${10}^{5.4-5.7}$Msun based on its orbit in the Milky Way. A preferential loss of first-population stars could explain the high fraction of second-population stars at the present time. Our results emphasize the importance of considering mass loss when studying globular clusters and their enrichment patterns. 

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