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1. Atomic Transition Probabilities for UV and Optical Lines of Gd ii *

   https://doi.org/10.3847/1538-4365/adbf1e  

   Voith, G T; Den_Hartog, E A; Roederer, I U (April 2025, The Astrophysical Journal Supplement Series)

   Abstract We report new branching fraction (BF) measurements for 156 ultraviolet and optical transitions of Gdii. These transitions range in wavelength (wavenumber) from 2574 to 6766 Å (38,838–14,777 cm⁻¹) and originate in one odd-parity and 11 even-parity upper levels. Nine of the 12 levels, accounting for 126 of the 156 transitions, are studied for the first time. BFs are determined for three levels studied previously for the purpose of comparison. The levels studied for the first time are high lying, ranging in energy from 36,845 to 40,774 cm⁻¹. The BFs are determined from emission spectra from two different high-resolution spectrometers. These are combined with radiative lifetimes reported in an earlier study to produce a set of transition probabilities and log(gf) values with accuracy ranging from 5% to 30%. Comparison is made to experimental and theoretical transition probabilities from the literature where such data exist. Abundances derived from these new log(gf) values for 21 Gdiilines in two metal-poor stars yield results consistent with previous studies, and they demonstrate that the new log(gf) values can be used in stellar abundance analysis as a self-consistent extension of previous work. 

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2. Atomic Transition Probabilities for Transitions of Si i and Si ii and the Silicon Abundances of Several Very Metal-poor Stars ^∗

   https://doi.org/10.3847/1538-4365/acb642  

   Den Hartog, E. A.; Lawler, J. E.; Sneden, C.; Roederer, I. U.; Cowan, J. J. (March 2023, The Astrophysical Journal Supplement Series)

   Abstract We report new measurements of branching fractions for 20 UV and blue lines in the spectrum of neutral silicon (Si i ) originating in the 3 s 2 3 p 4 s 3 P o 1,2 , 1 P o 1 , and 3 s 3 p 3 1 D o 1,2 upper levels. Transitions studied include both strong, nearly pure LS multiplets as well as very weak spin-forbidden transitions connected to these upper levels. We also report a new branching fraction measurement of the 4 P 1/2 – 2 P o 1/2,3/2 intercombination lines in the spectrum of singly ionized silicon (Si ii ). The weak spin-forbidden lines of Si i and Si ii provide a stringent test on recent theoretical calculations, to which we make comparison. The branching fractions from this study are combined with previously reported radiative lifetimes to yield transition probabilities and log( gf ) values for these lines. We apply these new measurements to abundance determinations in five metal-poor stars. 

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3. Analysis of $$ {\Lambda}_b^0 $$ → pK−μ+μ− decays

   https://doi.org/10.1007/JHEP12(2024)147  

   Aaij, R; Abdelmotteleb, A_S W; Abellan_Beteta, C; Abudinén, F; Ackernley, T; Adefisoye, A A; Adeva, B; Adinolfi, M; Adlarson, P; Agapopoulou, C; et al (December 2024, Journal of High Energy Physics)

   A<sc>bstract</sc> The differential branching fraction and angular coefficients of$$ {\Lambda}_b^0 $$ ${\Lambda }_b^0$→pK⁻μ⁺μ⁻decays are measured in bins of the dimuon mass squared and dihadron mass. The analysis is performed using a data set corresponding to 9 fb⁻¹of integrated luminosity collected with the LHCb detector between 2011 and 2018. The data are consistent with receiving contributions from a mixture of Λ resonances with different spin-parity quantum numbers. The angular coefficients show a pattern of vector-axial vector interference that is a characteristic of the type of flavour-changing neutral-current transition relevant for these decays. 

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4. A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE): Impact of Galaxies on the Circumgalactic Medium Metal Enrichment at z > 6 Using the JWST and VLT

   https://doi.org/10.3847/2041-8213/ad23e7  

   Zou, Siwei; Cai, Zheng; Wang, Feige; Fan, Xiaohui; Champagne, Jaclyn B; Hennawi, Joseph F; Schindler, Jan-Torge; Farina, Emanuele Paolo; Yang, Jinyi; Inayoshi, Kohei; et al (February 2024, The Astrophysical Journal Letters)

   Abstract We characterize the multiphase circumgalactic medium (CGM) and galaxy properties atz= 6.0–6.5 in four quasar fields from the James Webb Space Telescope A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE) program. We use the Very Large Telescope/X-shooter spectra of quasar J0305–3150 to identify one new metal absorber atz= 6.2713 with multiple transitions (Oi, Mgii, Feii,and Cii). They are combined with the published absorbing systems in Davies et al. at the same redshift range to form a sample of nine metal absorbers atz= 6.03–6.49. We identify eight galaxies within 1000 km s⁻¹and 350 kpc around the absorbing gas from the ASPIRE spectroscopic data, with their redshifts secured by [Oiii] (λλ4959, 5007) doublets and Hβemission lines. Our spectral energy distribution fitting indicates that the absorbing galaxies have stellar masses ranging from 10^7.2to 10^8.8M_⊙and metallicity between 0.02 and 0.4 solar. Notably, thez= 6.2713 system in the J0305–3150 field resides in a galaxy overdensity region, which contains two (tentatively) merging galaxies within 350 kpc and seven galaxies within 1 Mpc. We measure the relative abundances ofαelements to iron ([α/Fe]) and find that the CGM gas in the most overdense region exhibits a lower [α/Fe] ratio. Our modeling of the galaxy’s chemical abundance favors a top-heavy stellar initial mass function and hints that we may be witnessing the contribution of the first generation of Population III stars to the CGM at the end of the reionization epoch. 

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5. Iron-Peak Element Abundances in Warm Very Metal-Poor Stars

   https://doi.org/10.3847/1538-4357/accd62  

   Sneden, Christopher; Boesgaard, Ann M.; Cowan, John J.; Roederer, Ian U.; Den Hartog, Elizabeth A.; Lawler, James E. (July 2023, The Astrophysical journal)

   We have derived new detailed abundances of Mg, Ca, and the Fe-group elements Sc through Zn (Z = 21-30) for 37 main sequence turnoff very metal-poor stars ([Fe/H] . ~<2.1). We analyzed Keck HIRES optical and near-UV high signal-to-noise spectra originally gathered for a beryllium abundance survey. Using typically ~400 Fe-group lines with accurate laboratory transition probabilities for each star, we have determined accurate LTE metallicities and abundance ratios for neutral and ionized species of the 10 Fe-group elements as well as alpha elements Mg and Ca. We nd good neutral/ion abundance agreement for the 6 elements that have detectable transitions of both species in our stars in the 3100-5800 A range. Earlier reports of correlated Sc-Ti-V relative overabundances are confirmed, and appear to slowly increase with decreasing metallicity. To this element trio we add Zn; it also appears to be increasingly overabundant in the lowest metallicity regimes. Co appears to mimic the behavior of Zn, but issues surrounding its abundance reliability cloud its interpretation. 

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