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1. The open cluster NGC 2345: a study of chemical abundances with near-infrared IGRINS high-resolution spectra

   https://doi.org/10.1093/mnras/stad3280  

   Holanda, N. ; Roriz, M. P. ; Drake, N. A. ; Junqueira, S. ; Daflon, S. ; da Silva, J. R. P. ; Pereira, C. B. ( October 2023 , Monthly Notices of the Royal Astronomical Society)

   Open clusters are relatively young and numerous. These systems are distributed throughout the Galactic disc and provide insights on the chemistry of the Milky Way. In this study, we provide a near-infrared spectroscopic analysis of four stars of the young open cluster NGC 2345. Our infrared data present a resolving power of R ≈ 45 000, covering the H- and K-bands (1.5–2.5 μm), and high-signal-to-noise ratio, which are gathered with the Immersion Grating Infrared Spectrograph (IGRINS) at the Gemini Observatory. From atmospheric parameters previously derived via optical spectroscopy, we obtain abundances for C (12C16O), N (12C14N), O (16OH), F (H19F), Na, Mg, Al, Si, P, S, K, Ca, Sc, Ti, Cr, Fe, Ni, Ce, Nd, and Yb. Additionally, the 12C/13C (13C16O), 16O/17O (12C17O), and 16O/18O (12C18O) isotopic ratios are obtained. We compare the infrared results with a previous work based on optical spectral analysis, but chemical species such as F, S, P, K, and Yb are determined for the first time in stars of NGC 2345. We also confirm a low metallicity ([Fe/H]  =  −0.32 ± 0.04) and slight enrichment in s-process elements, as already noticed in works available in the literature, but we do not find any enrichment in F. Our results demonstrate excellent agreement between our measured isotopic ratios 12C/13C and 16C/17O and models of stellar nucleosynthesis, while we find that the abundance of 18O is overestimated in comparison to our measurements. Finally, we assess our findings in comparison to the chemical patterns observed in open clusters, classified by both their age and Galactocentric distances, and highlight the need for a more comprehensive sample of young clusters within the 9–11 kpc range for a proper comparison.

    

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2. Assessment of interatomic parameters for the reproduction of borosilicate glass structures via DFT‐GIPAW calculations

   https://doi.org/10.1111/jace.16655  

   Fortino, Mariagrazia ; Berselli, Alessandro ; Stone‐Weiss, Nicholas ; Deng, Lu ; Goel, Ashutosh ; Du, Jincheng ; Pedone, Alfonso ( June 2019 , Journal of the American Ceramic Society)

   Borates and borosilicates are potential candidates for the design and development of glass formulations with important industrial and technological applications. A major challenge that retards the pace of development of borate/borosilicate based glasses using predictive modeling is the lack of reliable computational models to predict the structure‐property relationships in these glasses over a wide compositional space. A major hindrance in this pursuit has been the complexity of boron‐oxygen bonding due to which it has been difficult to develop adequate B–O interatomic potentials. In this article, we have evaluated the performance of three B–O interatomic potential models recently developed by Bauchy et al [J.Non‐Cryst. Solids, 2018, 498, 294–304], Du et al [J. Am. Ceram. Soc.https://doi.org/10.1111/jace.16082] and Edèn et al [Phys. Chem. Chem. Phys., 2018, 20, 8192–8209] aiming to reproduce the short‐to‐medium range structures of sodium borosilicate glasses in the system 25 Na₂OxB₂O₃(75 − x) SiO₂(x = 0‐75 mol%). To evaluate the different force fields, we have computed at the density functional theory level the NMR parameters of¹¹B,²³Na, and²⁹Si of the models generated with the three potentials and the simulated MAS NMR spectra compared with the experimental counterparts. It was observed that the rigid ionic models proposed by Bauchy and Du can both reliably reproduce the partitioning between BO₃and BO₄species of the investigated glasses, along with the local environment around sodium in the glass structure. However, they do not accurately reproduce the second coordination sphere of silicon ions and the Si–O–T (T = Si, B) and B‐O‐T distribution angles in the investigated compositional space which strongly affect the NMR parameters and final spectral shape. On the other hand, the core‐shell parameterization model proposed by Edén underestimates the fraction of BO₄species of the glass with composition 25Na₂O 18.4B₂O₃56.6SiO₂but can accurately reproduce the shape of the¹¹B and²⁹Si MAS‐NMR spectra of the glasses investigations due to the narrower B–O–T and Si‐O‐T bond angle distributions. Finally, the effect of the number of boron atoms (also distinguishing the BO₃and BO₄units) in the second coordination sphere of the network former cations on the NMR parameters have been evaluated.

    

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3. Stellar Neutrino Emission across the Mass–Metallicity Plane

   https://doi.org/10.3847/1538-4365/ad0787  

   Farag, Ebraheem ; Timmes, F. X. ; Chidester, Morgan T. ; Anandagoda, Samalka ; Hartmann, Dieter H. ( December 2023 , The Astrophysical Journal Supplement Series)

   We explore neutrino emission from nonrotating, single-star models across six initial metallicities and 70 initial masses from the zero-age main sequence to the final fate. Overall, across the mass spectrum, we find metal-poor stellar models tend to have denser, hotter, and more massive cores with lower envelope opacities, larger surface luminosities, and larger effective temperatures than their metal-rich counterparts. Across the mass–metallicity plane we identify the sequence (initial CNO →¹⁴N →²²Ne →²⁵Mg →²⁶Al →²⁶Mg →³⁰P →³⁰Si) as making primary contributions to the neutrino luminosity at different phases of evolution. For the low-mass models we find neutrino emission from the nitrogen flash and thermal pulse phases of evolution depend strongly on the initial metallicity. For the high-mass models, neutrino emission at He-core ignition and He-shell burning depends strongly on the initial metallicity. Antineutrino emission during C, Ne, and O burning shows a strong metallicity dependence with²²Ne(α,n)²⁵Mg providing much of the neutron excess available for inverse-βdecays. We integrate the stellar tracks over an initial mass function and time to investigate the neutrino emission from a simple stellar population. We find average neutrino emission from simple stellar populations to be 0.5–1.2 MeV electron neutrinos. Lower metallicity stellar populations produce slightly larger neutrino luminosities and averageβdecay energies. This study can provide targets for neutrino detectors from individual stars and stellar populations. We provide convenient fitting formulae and open access to the photon and neutrino tracks for more sophisticated population synthesis models.

    

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4. UVES analysis of red giants in the bulge globular cluster NGC 6522

   Barbuy, B ; Cantelli, E ; Muniz, L ; Souza, S.~O ; Chiappini, C ; Hirschi, R ; Cescutti, G ; Pignatari, M ; Ortolani, S ; Kerber, L ; et al ( July 2021 , ArXivorg)

   null (Ed.)

   Context. NGC 6522 is a moderately metal-poor bulge globular cluster ([Fe/H]∼−1.0), and it is a well-studied representative among a number of moderately metal-poor blue horizontal branch clusters located in the bulge. The NGC 6522 abundance pattern can give hints on the earliest chemical enrichment in the central Galaxy. Aims. The aim of this study is to derive abundances of the light elements C and N; alpha elements O, Mg, Si, Ca, and Ti; odd-Z elements Na and Al; neutron-capture elements Y, Zr, Ba, La, and Nd; and the r-process element Eu. We verify if there are first- and second-generation stars: we find clear evidence of Na-Al, Na-N, and Mg-Al correlations, while we cannot identify the Na-O anti-correlation from our data. Methods. High-resolution spectra of six red giants in the bulge globular cluster NGC 6522 were obtained at the 8m VLT UT2-Kueyen telescope with both the UVES and GIRAFFE spectrographs in FLAMES+UVES configuration. In light of Gaia data, it turned out that two of them are non-members, but these were also analysed. Spectroscopic parameters were derived through the excitation and ionisation equilibrium of Fe i and Fe ii lines from UVES spectra. The abundances were obtained with spectrum synthesis. Comparisons of abundances derived from UVES and GIRAFFE spectra were carried out. Results. The present analysis combined with previous UVES results gives a mean radial velocity of vhel = −15.62±7.7 km s−1 and a r metallicity of [Fe/H] = −1.05±0.20 for NGC 6522. Mean abundances of alpha elements for the present four member stars are enhanced with [O/Fe]=+0.38, [Mg/Fe]=≈+0.28, [Si/Fe]≈+0.19, and [Ca/Fe]≈+0.13, together with the iron-peak element [Ti/Fe]≈+0.13, and the r-process element [Eu/Fe]=+0.40. The neutron-capture elements Y, Zr, Ba, and La show enhancements in the +0.08 < [Y/Fe] < +0.90, 0.11 < [Zr/Fe] < +0.50, 0.00 < [Ba/Fe] < +0.63, 0.00 < [La/Fe] < +0.45, and -0.10 < [Nd/Fe] < +0.70 ranges. We also discuss the spread in heavy-element abundances. 

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5. UVES analysis of red giants in the bulge globular cluster NGC 6522

   https://doi.org/10.1051/0004-6361/202140815  

   Barbuy, B. ; Cantelli, E. ; Muniz, L. ; Souza, S. O. ; Chiappini, C. ; Hirschi, R. ; Cescutti, G. ; Pignatari, M. ; Ortolani, S. ; Kerber, L. ; et al ( October 2021 , Astronomy & Astrophysics)

   Context. NGC 6522 is a moderately metal-poor bulge globular cluster ([Fe/H] ~ −1.0), and it is a well-studied representative among a number of moderately metal-poor blue horizontal branch clusters located in the bulge. The NGC 6522 abundance pattern can give hints on the earliest chemical enrichment in the central Galaxy. Aims. The aim of this study is to derive abundances of the light elements C and N; alpha elements O, Mg, Si, Ca, and Ti; odd-Z elements Na and Al; neutron-capture elements Y, Zr, Ba, La, and Nd; and the r -process element Eu. We verify if there are first- and second-generation stars: we find clear evidence of Na–Al, Na–N, and Mg–Al correlations, while we cannot identify the Na–O anti-correlation from our data. Methods. High-resolution spectra of six red giants in the bulge globular cluster NGC 6522 were obtained at the 8m VLT UT2-Kueyen telescope with both the UVES and GIRAFFE spectrographs in FLAMES+UVES configuration. In light of Gaia data, it turned out that two of them are non-members, but these were also analysed. Spectroscopic parameters were derived through the excitation and ionisation equilibrium of Fe  I and Fe  II lines from UVES spectra. The abundances were obtained with spectrum synthesis. Comparisons of abundances derived from UVES and GIRAFFE spectra were carried out. Results. The present analysis combined with previous UVES results gives a mean radial velocity of v r hel = −15.62±7.7 km s −1 and a metallicity of [Fe/H] = −1.05 ± 0.20 for NGC 6522. Mean abundances of alpha elements for the present four member stars are enhanced with [O/Fe] = +0.38, [Mg/Fe] = ≈+0.28, [Si/Fe] ≈ +0.19, and [Ca/Fe] ≈ +0.13, together with the iron-peak element [Ti/Fe] ≈ +0.13, and the r -process element [Eu/Fe] = +0.40. The neutron-capture elements Y, Zr, Ba, and La show enhancements in the +0.08 < [Y/Fe] < +0.90, 0.11 < [Zr/Fe] < +0.50, 0.00 < [Ba/Fe] < +0.63, 0.00 < [La/Fe] < +0.45, and −0.10 < [Nd/Fe] < +0.70 ranges. We also discuss the spread in heavy-element abundances. 

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