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1. The Open Cluster Chemical Abundances and Mapping Survey. VI. Galactic Chemical Gradient Analysis from APOGEE DR17

   https://doi.org/10.3847/1538-3881/ac7ce5  

   Myers, Natalie; Donor, John; Spoo, Taylor; Frinchaboy, Peter M.; Cunha, Katia; Price-Whelan, Adrian M.; Majewski, Steven R.; Beaton, Rachael L.; Zasowski, Gail; O’Connell, Julia; et al (August 2022, The Astronomical Journal)

   Abstract The goal of the Open Cluster Chemical Abundances and Mapping (OCCAM) survey is to constrain key Galactic dynamic and chemical evolution parameters by the construction and analysis of a large, comprehensive, uniform data set of infrared spectra for stars in hundreds of open clusters. This sixth contribution from the OCCAM survey presents analysis of SDSS/APOGEE Data Release 17 (DR17) results for a sample of stars in 150 open clusters, 94 of which we designate to be “high-quality” based on the appearance of their color–magnitude diagram. We find the APOGEE DR17-derived [Fe/H] values to be in good agreement with those from previous high-resolution spectroscopic open cluster abundance studies. Using a subset of the high-quality sample, the Galactic abundance gradients were measured for 16 chemical elements, including [Fe/H], for both Galactocentric radius ( R GC ) and guiding center radius ( R guide ). We find an overall Galactic [Fe/H] versus R GC gradient of −0.073 ± 0.002 dex kpc −1 over the range of 6 > R GC < 11.5 kpc, and a similar gradient is found for [Fe/H] versus R guide . Significant Galactic abundance gradients are also noted for O, Mg, S, Ca, Mn, Na, Al, K, and Ce. Our large sample additionally allows us to explore the evolution of the gradients in four age bins for the remaining 15 elements. 

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2. Exploring the S-process History in the Galactic Disk: Cerium Abundances and Gradients in Open Clusters from the OCCAM/APOGEE Sample

   https://doi.org/10.3847/1538-4357/ac4254  

   Sales-Silva, J. V.; Daflon, S.; Cunha, K.; Souto, D.; Smith, V. V.; Chiappini, C.; Donor, J.; Frinchaboy, P. M.; García-Hernández, D. A.; Hayes, C.; et al (February 2022, The Astrophysical Journal)

   Abstract The APOGEE Open Cluster Chemical Abundances and Mapping survey is used to probe the chemical evolution of the s-process element cerium in the Galactic disk. Cerium abundances were derived from measurements of Ce ii lines in the APOGEE spectra using the Brussels Automatic Code for Characterizing High Accuracy Spectra in 218 stars belonging to 42 open clusters. Our results indicate that, in general, for ages < 4 Gyr, younger open clusters have higher [Ce/Fe] and [Ce/ α -element] ratios than older clusters. In addition, metallicity segregates open clusters in the [Ce/X]–age plane (where X can be H, Fe, or the α -elements O, Mg, Si, or Ca). These metallicity-dependent relations result in [Ce/Fe] and [Ce/ α ] ratios with ages that are not universal clocks. Radial gradients of [Ce/H] and [Ce/Fe] ratios in open clusters, binned by age, were derived for the first time, with d [Ce/H]/ d R GC being negative, while d [Ce/Fe]/ d R GC is positive. [Ce/H] and [Ce/Fe] gradients are approximately constant over time, with the [Ce/Fe] gradient becoming slightly steeper, changing by ∼+0.009 dex kpc −1 Gyr −1 . Both the [Ce/H] and [Ce/Fe] gradients are shifted to lower values of [Ce/H] and [Ce/Fe] for older open clusters. The chemical pattern of Ce in open clusters across the Galactic disk is discussed within the context of s-process yields from asymptotic giant branch (AGB) stars, gigayear time delays in Ce enrichment of the interstellar medium, and the strong dependence of Ce nucleosynthesis on the metallicity of its AGB stellar sources. 

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3. Modeling the Ages and Chemical Abundances of Elliptical Galaxies

   https://doi.org/10.3847/1538-4357/adc4e6  

   Gountanis, Nicole Marcelina; Weinberg, David H; Beverage, Aliza G; Sandford, Nathan R; Conroy, Charlie; Kriek, Mariska (May 2025, The Astrophysical Journal)

   Abstract Spectroscopic studies of elliptical galaxies show that their stellar population ages, mean metallicity, andαenhancement traced by [Mg/Fe] all increase with galaxy stellar mass or velocity dispersion. We use one-zone galactic chemical evolution (GCE) models with a flexible star formation history (SFH) to model the age, [Mg/H], and [Mg/Fe] inferred from simple stellar population (SSP) fits to observed ellipticals atz∼ 0 andz∼ 0.7. We show that an SSP fit to the spectrum computed from a full GCE model gives ages and abundances close to the light-weighted, logarithmically averaged values of the composite stellar population, 〈age〉, 〈[Mg/H]〉, and 〈[Mg/Fe]〉. With supernova Mg and Fe yields fixed to values motivated by Milky Way stellar populations, we find that predicted 〈[Mg/H]〉–〈age〉 and 〈[Mg/Fe]〉–〈age〉 relations are surprisingly insensitive to SFH parameters: Older galaxies have higher 〈[Mg/Fe]〉, but the detailed form of the SFH has limited impact. The star formation efficiency (SFE) and outflow efficiency affect the early and late evolution of 〈[Mg/H]〉, respectively; explaining observed trends requires higher SFE and lower outflows in more massive galaxies. With core-collapse supernova yields calibrated to the plateau [Mg/Fe]_cc≈ 0.45 observed in many Milky Way studies, our models underpredict the observed 〈[Mg/Fe]〉 ratios of ellipticals by 0.05–0.1 dex. Increasing the core-collapse yield ratio to [Mg/Fe]_cc= 0.55 improves the agreement, though the models remain below the data. We discuss potential resolutions of this discrepancy, including the possibility that many ellipticals terminate their star formation with a self-enriching, terminating burst that reduces the light-weighted age and boosts 〈[Mg/Fe]〉. 

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4. Detailed Chemical Abundances for a Benchmark Sample of M Dwarfs from the APOGEE Survey

   https://doi.org/10.3847/1538-4357/ac4891  

   Souto, Diogo; Cunha, Katia; Smith, Verne V.; Prieto, C. Allende; Covey, Kevin; García-Hernández, D. A.; Holtzman, Jon A.; Jönsson, Henrik; Mahadevan, Suvrath; Majewski, Steven R.; et al (March 2022, The Astrophysical Journal)

   Abstract Individual chemical abundances for 14 elements (C, O, Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, Fe, and Ni) are derived for a sample of M dwarfs using high-resolution, near-infrared H -band spectra from the Sloan Digital Sky Survey-IV/Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. The quantitative analysis included synthetic spectra computed with 1D LTE plane-parallel MARCS models using the APOGEE Data Release 17 line list to determine chemical abundances. The sample consists of 11 M dwarfs in binary systems with warmer FGK dwarf primaries and 10 measured interferometric angular diameters. To minimize atomic diffusion effects, [X/Fe] ratios are used to compare M dwarfs in binary systems and literature results for their warmer primary stars, indicating good agreement (<0.08 dex) for all studied elements. The mean abundance difference in primaries minus this work’s M dwarfs is −0.05 ± 0.03 dex. It indicates that M dwarfs in binary systems are a reliable way to calibrate empirical relationships. A comparison with abundance, effective temperature, and surface gravity results from the APOGEE Stellar Parameter and Chemical Abundances Pipeline (ASPCAP) Data Release 16 finds a systematic offset of [M/H], T eff , log g = +0.21 dex, −50 K, and 0.30 dex, respectively, although ASPCAP [X/Fe] ratios are generally consistent with this study. The metallicities of the M dwarfs cover the range of [Fe/H] = −0.9 to +0.4 and are used to investigate Galactic chemical evolution via trends of [X/Fe] as a function of [Fe/H]. The behavior of the various elemental abundances [X/Fe] versus [Fe/H] agrees well with the corresponding trends derived from warmer FGK dwarfs, demonstrating that the APOGEE spectra can be used to examine Galactic chemical evolution using large samples of selected M dwarfs. 

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5. Chemical Abundances of M and G Dwarfs in the Hyades and Coma Berenices Open Clusters from APOGEE Spectra

   https://doi.org/10.3847/1538-4357/ae0930  

   Vilar, Deusalete; Souto, Diogo; Cunha, Katia; Andrade-Silva, Anderson; Loaiza-Tacuri, Verónica; Wanderley, Fábio; Smith, Verne V; Grilo, Vinicius; Martinez, Cintia F; Rojas-Ayala, Bárbara; et al (November 2025, The Astrophysical Journal)

   Open clusters are one of the best astrophysical laboratories we have available for stellar astrophysics studies. This work presents metallicities and individual abundances for 14 M dwarfs and six G dwarfs from two well-known open clusters: Hyades and Coma Berenices. Our analysis is based on near-infrared (1.51–1.69μm), high-resolution (R∼ 22,500) spectra obtained from the Sloan Digital Sky Survey (SDSS) IV/APOGEE Survey. Using one-dimensional, plane-parallel MARCS model atmospheres, the APOGEE line list, and the Turbospectrum radiative transfer code in local thermodynamic equilibrium, we derived spectroscopic stellar parameters for the M dwarfs, along with abundances of 13 elements (C, O, Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, and Fe) for both M and G dwarfs. We find a high degree of chemical homogeneity within each cluster when comparing abundances derived from M and G dwarfs:δ[M/H] (M dwarfs–G dwarfs) of 0.01 ± 0.04, and 0.02 ± 0.03 for the Hyades and Coma Berenices, respectively. The overall cluster metallicities derived from M dwarfs (Hyades: 0.16 ± 0.03 and Coma Berenices: 0.02 ± 0.06) are consistent with previous literature determinations. Finally, we demonstrate the value of M dwarfs as key tracers in Galactic archeology, emphasizing their potential for studying Galactic metallicity gradients and chemical evolution. 

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