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1. Correction to: Conversions between gas-phase metallicities in MaNGA

   https://doi.org/10.1093/mnras/stae1765  

   Scudder, Jillian M; Ellison, Sara L; El Meddah El Idrissi, Loubna; Poetrodjojo, Henry (August 2024, Monthly Notices of the Royal Astronomical Society)

   A brief correction to a publication published in 2020, which created a 0.03 dex offset in published calibrations. 

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2. Metallicities from high-resolution spectra of 49 RR Lyrae variables

   https://doi.org/10.1093/mnras/stab857  

   Gilligan, Christina K; Chaboyer, Brian; Marengo, Massimo; Mullen, Joseph P; Bono, Giuseppe; Braga, Vittorio F; Crestani, Juliana; Dall’Ora, Massimo; Fiorentino, Giuliana; Monelli, Matteo; et al (April 2021, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT Accurate metallicities of RR Lyrae are extremely important in constraining period–luminosity–metallicity (PLZ) relationships, particularly in the near-infrared. We analyse 69 high-resolution spectra of Galactic RR Lyrae stars from the Southern African Large Telescope. We measure metallicities of 58 of these RR Lyrae stars with typical uncertainties of 0.15 dex. All but one RR Lyrae in this sample has accurate ($$\sigma _{\varpi }\lesssim 10{{\ \rm per\ cent}}$$) parallax from Gaia. Combining these new high-resolution spectroscopic abundances with similar determinations from the literature for 93 stars, we present new PLZ relationships in WISE W1 and W2 magnitudes, and the Wesenheit magnitudes W(W1, V − W1) and W(W2, V − W2). 

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3. Condensation at Varying Total Pressures and Metallicities: Rare Earth Elements

   Lodders, K.; Fegley, B. (July 2017, LPI Contribution No. 1987)

   Condensation of the ultrarefractory REE as oxides before Ca-bearing condensates at lower total pressures and [Fe/H] removes the need for removal of hibonite or perovskite from equilibrium with gas within an extremely small T interval after they become stable. 

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4. Improving White Dwarfs as Chronometers with Gaia Parallaxes and Spectroscopic Metallicities

   https://doi.org/10.3847/1538-4357/ac5ac0  

   Moss, Adam; von Hippel, Ted; Robinson, Elliot; El-Badry, Kareem; Stenning, David C.; van Dyk, David; Fouesneau, Morgan; Bailer-Jones, Coryn A. L.; Jeffery, Elizabeth; Sargent, Jimmy; et al (April 2022, The Astrophysical Journal)

   Abstract White dwarfs (WDs) offer unrealized potential in solving two problems in astrophysics: stellar age accuracy and precision. WD cooling ages can be inferred from surface temperatures and radii, which can be constrained with precision by high-quality photometry and parallaxes. Accurate and precise Gaia parallaxes along with photometric surveys provide information to derive cooling and total ages for vast numbers of WDs. Here we analyze 1372 WDs found in wide binaries with main-sequence (MS) companions and report on the cooling and total age precision attainable in these WD+MS systems. The total age of a WD can be further constrained if its original metallicity is known because the MS lifetime depends on metallicity at fixed mass, yet metallicity is unavailable via spectroscopy of the WD. We show that incorporating spectroscopic metallicity constraints from 38 wide binary MS companions substantially decreases internal uncertainties in WD total ages compared to a uniform constraint. Averaged over the 38 stars in our sample, the total (internal) age uncertainty improves from 21.04% to 16.77% when incorporating the spectroscopic constraint. Higher mass WDs yield better total age precision; for eight WDs with zero-age MS masses ≥2.0M_⊙, the mean uncertainty in total ages improves from 8.61% to 4.54% when incorporating spectroscopic metallicities. We find that it is often possible to achieve 5% total age precision for WDs with progenitor masses above 2.0M_⊙if parallaxes with ≤1% precision and Pan-STARRSg,r, andiphotometry with ≤0.01 mag precision are available. 

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5. Metallicities of 20 Million Giant Stars Based on Gaia XP Spectra

   https://doi.org/10.3847/1538-4365/add5e3  

   Yang_杨, Lin 琳; Yuan_苑, Haibo 海波; Huang_黄, Bowen 博闻; Zhang_张, Ruoyi 若羿; Beers, Timothy C; Xiao_肖, Kai 凯; Xu_徐, Shuai 帅; Huang_黄, Yang 样; Xiang_向, Maosheng 茂盛; Zhang_张, Meng 萌; et al (June 2025, The Astrophysical Journal Supplement Series)

   Abstract We design an uncertainty-aware cost-sensitive neural network (UA-CSNet) to estimate metallicities from dereddened and corrected Gaia BP/RP (XP) spectra for giant stars. This method accounts for both stochastic errors in the input spectra and the imbalanced density distribution in [Fe/H] values. With a specialized architecture and training strategy, the UA-CSNet improves the precision of the predicted metallicities, especially for very metal-poor (VMP; [Fe/H] ≤ −2.0) stars. With the PASTEL catalog as the training sample, our model can estimate metallicities down to [Fe/H] ∼ −4. We compare our estimates with a number of external catalogs and conduct tests using star clusters, finding overall good agreement. We also confirm that our estimates for VMP stars are unaffected by carbon enhancement. Applying the UA-CSNet, we obtain reliable and precise metallicity estimates for approximately 20 million giant stars, including 360,000 VMP stars and 50,000 extremely metal-poor ([Fe/H] ≤ −3.0) stars. The resulting catalog is publicly available via the Chinese Virtual Observatory at doi: 10.12149/101604. This work highlights the potential of low-resolution spectra for metallicity estimation and provides a valuable data set for studying the formation and chemodynamical evolution of our Galaxy. 

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