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1. WAIS Divide Ice Core δ ¹⁵ N(NO ₃ ⁻ ) Variability Over the Last Glacial‐Interglacial Cycle: Controlling Factors and Implications for Retrieving Surface Mass Balance Using Ice Core δ ¹⁵ N(NO ₃ ⁻ ) Records

   https://doi.org/10.1029/2025JD043712  

   Jiang, Zhuang; Alexander, Becky; McConnell, Joseph R; Schauer, Andrew; Geng, Lei (July 2025, Journal of Geophysical Research: Atmospheres)

   Abstract Ice core nitrate can serve as a valuable tracer for past atmospheric nitrogen oxide (NO_x) and oxidant concentrations. However, photolysis‐driven postdepositional processing can alter ice core nitrate signals and complicate their interpretation. We present a new nitrogen isotope (δ¹⁵N) record of nitrate measured in the West Antarctic Ice Sheet (WAIS) Divide ice core covering the last glacial period and Holocene. The glacialδ¹⁵N(NO₃⁻) is substantially higher than the Holoceneδ¹⁵N(NO₃⁻), with a glacial‐interglacial difference of (26.6 ± 5.7) ‰. All samples exhibit a strong negative correlation betweenδ¹⁵N(NO₃⁻) and the snow accumulation rate, suggesting that postdepositional processing is the primary driver of theδ¹⁵N(NO₃⁻) variability. Photochemical model calculations indicate that changes in the degree of postdepositional processing can fully explain the observed glacial‐interglacialδ¹⁵N(NO₃⁻) difference, with 12.7% and 31.8% of nitrate mass loss during the Holocene and glacial climate, respectively. Comparison with the Greenland GISP2δ¹⁵N(NO₃⁻) record indicates that the glacial level of postdepositional modification was higher at WAIS Divide despite its snow accumulation rate was twice that at Summit, Greenland. This is due to the higher light‐absorbing impurity contents in the GISP2 ice core that reduced postdepositional losses. We also assess the ability of usingδ¹⁵N(NO₃⁻) for past surface mass balance (SMB) reconstruction at WAIS Divide. We find this proxy is reliable for regions/periods with snow accumulation rates lower than 150 kg m⁻²a⁻¹. While exceeding this threshold, the assumption of a constantδ¹⁵N of initially deposited nitrate is no longer valid, leading to significant bias in SMB reconstruction such as WAIS Divide. 

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2. Direct Measurement of ⁵⁹ Cu( p , α ) ⁵⁶ Ni Precludes a Strong NiCu Cycle in Type-I X-Ray Bursts

   https://doi.org/10.3847/1538-4357/ae3de6  

   Bhathi, N; Randhawa, J S; Kanungo, R; Refsgaard, J; Alcorta, M; Ahn, T; Andreoiu, C; Bardayan, D; Bhattacharjee, S S; Davids, B; et al (February 2026, The Astrophysical Journal)

   Abstract Model-observation comparisons of type-I X-ray bursts (XRBs) can reveal the properties of accreting neutron star systems, including the neutron star compactness. XRBs are powered by nuclear burning, and a handful of reactions have been shown to impact the model results. Reactions in the NiCu cycles, featuring a competition between⁵⁹Cu(p,γ)⁶⁰Zn and⁵⁹Cu(p,α)⁵⁶Ni, have been shown to be among the most important reactions as they are a critical checkpoint inrp-process flow and significantly impact the light curves and burst ashes. We report a direct measurement of⁵⁹Cu(p,α)⁵⁶Ni, bringing stringent constraints on this reaction rate. New results rule out a strong NiCu cycle in XRBs, with a negligible degree of recycling, ≤5% up to 1.5 GK. The new reaction rate, when varied within new uncertainty limits, shows no impact on one-zone XRB model light curves tailored for clocked-bursterGS1826–24, hence removing an important nuclear physics uncertainty in the model-observation comparison. 

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3. Improved thermonuclear rate of ⁴² Ti( p , γ ) ⁴³ V and its astrophysical implication in the rp process

   https://doi.org/10.1051/0004-6361/202347054  

   Hou, S Q; Iliadis, C; Pignatari, M; Liu, J B; Trueman, T_C L; Li, J G; Xu, X X (September 2023, Astronomy & Astrophysics)

   Context.Accurate⁴²Ti(p,γ)⁴³V reaction rates are crucial for understanding the nucleosynthesis path of the rapid capture process (rpprocess) that occurs in X-ray bursts. Aims.We aim to improve the thermonuclear rates of⁴²Ti(p,γ)⁴³V based on more complete resonance information and a more accurate direct component, together with the recently released nuclear masses data. We also explore the impact of the newly obtained rates on therpprocess. Methods.We reevaluated the reaction rate of⁴²Ti(p,γ)⁴³V by the sum of the isolated resonance contribution instead of the Hauser-Feshbach statistical model. We used a Monte Carlo method to derive the associated uncertainties of new rates. The nucleosynthesis simulations were performed via the NuGrid post-processing code ppn. Results.The new rates differ from previous estimations due to the use of a series of updated resonance parameters and a direct S factor. Compared with the previous results from the Hauser-Feshbach statistical model, which assumes compound nucleus⁴³V with a sufficiently high-level density in the energy region of astrophysical interest, large differences exist over the entire temperature region ofrp-process interest, up to two orders of magnitude. We consistently calculated the photodisintegration rate using our new nuclear masses via the detailed balance principle, and found the discrepancies among the different reverse rates are much larger than those for the forward rate, up to ten orders of magnitude at the temperature of 10⁸K. Using a trajectory with a peak temperature of 1.95×10⁹K, we performed therp-process nucleosynthesis simulations to investigate the impact of the new rates. Our calculations show that the adoption of the new forward and reverse rates result in abundance variations for Sc and Ca of 128% and 49%, respectively, compared to the variations for the statistical model rates. On the other hand, the overall abundance pattern is not significantly affected. The results of using new rates also confirm that therp-process path does not bypass the isotope⁴³V. Conclusions.Our study found that the Hauser-Feshbach statistical model is inappropriate to the reaction rate evaluation for⁴²Ti(p,γ)⁴³V. The adoption of the new rates confirms that the reaction path of⁴²Ti(p,γ)⁴³V(p,γ)⁴⁴Cr(β⁺)⁴⁴V is a key branch of therpprocess in X-ray bursts. 

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4. ELVES-Field: Isolated Dwarf Galaxy Quenched Fractions Rise below M _∗  ≈ 10 ⁷ M _⊙

   https://doi.org/10.3847/2041-8213/ae4bdf  

   Carlsten, Scott G; Li_李, Jiaxuan 嘉轩; Greene, Jenny E; Drlica-Wagner, Alex; Danieli, Shany (April 2026, The Astrophysical Journal Letters)

   Abstract We use a new sample of low-mass (M_* < 10⁹ M_⊙) isolated galaxies from the Exploration of Local VolumE Survey-Field (ELVES-Field) to examine the star formation properties and sizes of field dwarf galaxies in the Local Volume (LV;D < 10 Mpc). This volume-limited sample was selected from nearly 3000 deg²of imaging, relying on surface brightness fluctuations to determine distances to the majority of the systems and is complete toM_* ≈ 10⁶ M_⊙. Across the surveyed area, we catalog over 2300 candidate LV dwarfs, of which we confirm 95 as genuine LV members and reject over 1600 as background contaminants, with the remaining 600 candidates still requiring a distance measurement. Of the confirmed LV dwarfs, 46 are either new discoveries or confirmed via a distance measurement for the first time here. We explore different environmental criteria to select isolated dwarfs but primarily focus on dwarfs that are >2 × R_virin projection from any known group withM_⋆ > 10⁹M_⊙. We find that, at higher dwarf masses (M_⋆ ≳ 10⁷M_⊙), essentially all field dwarfs are star forming as has been found before. In contrast, atM_⋆ ≲ 10⁷M_⊙, ∼30% of field dwarfs appear to be quenched. Finally, we find that isolated dwarfs are noticeably smaller (∼20%) than satellite dwarfs of the same stellar mass, regardless of quenched status. 

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5. Thermonuclear ²⁸ P(p, γ ) ²⁹ S reaction rate and astrophysical implication in ONe nova explosion

   https://doi.org/10.1051/0004-6361/202449536  

   Liu, J B; José, J; Hou, S Q; Pignatari, M; Trueman, T_C L; Longland, R; Li, J G; Bertulani, C A; Xu, X X (July 2024, Astronomy & Astrophysics)

   Context.An accurate²⁸P(p,γ)²⁹S reaction rate is crucial to defining the nucleosynthesis products of explosive hydrogen burning in ONe novae. Using the recently released nuclear mass of²⁹S, together with a shell model and a direct capture calculation, we reanalyzed the²⁸P(p,γ)²⁹S thermonuclear reaction rate and its astrophysical implication. Aims.We focus on improving the astrophysical rate for²⁸P(p,γ)²⁹S based on the newest nuclear mass data. Our goal is to explore the impact of the new rate and associated uncertainties on the nova nucleosynthesis. Methods.We evaluated this reaction rate via the sum of the isolated resonance contribution instead of the previously used Hauser-Feshbach statistical model. The corresponding rate uncertainty at different energies was derived using a Monte Carlo method. Nova nucleosynthesis is computed with the 1D hydrodynamic code SHIVA. Results.The contribution from the capture on the first excited state at 105.64 keV in²⁸P is taken into account for the first time. We find that the capture rate on the first excited state in²⁸P is up to more than 12 times larger than the ground-state capture rate in the temperature region of 2.5 × 10⁷K to 4 × 10⁸K, resulting in the total²⁸P(p,γ)²⁹S reaction rate being enhanced by a factor of up to 1.4 at ~1 × 10⁹K. In addition, the rate uncertainty has been quantified for the first time. It is found that the new rate is smaller than the previous statistical model rates, but it still agrees with them within uncertainties for nova temperatures. The statistical model appears to be roughly valid for the rate estimation of this reaction in the nova nucleosynthesis scenario. Using the 1D hydrodynamic code SHIVA, we performed the nucleosynthesis calculations in a nova explosion to investigate the impact of the new rates of²⁸P(p,γ)²⁹S. Our calculations show that the nova abundance pattern is only marginally affected if we use our new rates with respect to the same simulations but statistical model rates. Finally, the isotopes whose abundance is most influenced by the present²⁸P(p,γ)²⁹S uncertainty are²⁸Si,^33,34S,^35,37Cl, and³⁶Ar, with relative abundance changes at the level of only 3% to 4%. 

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