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1. Dimming the Lights: 2D Simulations of Deflagrations of Hybrid C/O/Ne White Dwarfs Using FLASH

   https://doi.org/10.3847/1538-4357/acf658  

   Feldman, Catherine; Gutierrez, Nathanael; Eisenberg, Ellis; Willcox, Donald E.; Townsley, Dean M.; Calder, Alan C. (December 2023, The Astrophysical Journal)

   Abstract The dimmest and most numerous outlier of the Type Ia supernova population, the Type Iax event, is increasingly being found in the results of observational campaigns. There is currently no single accepted model to describe these events. This 2D study explores the viability of modeling Type Iax events as a hybrid C/O/Ne white dwarf progenitor undergoing a deflagration using the multiphysics software FLASH. This hybrid was created using the stellar evolution code MESA, and its C-depleted core and mixed structure have demonstrated lower yields than traditional C/O progenitors in previous deflagration-to-detonation studies. To generate a sample, 30 “realizations” of this simulation were performed, the only difference being the shape of the initial match head used to start the deflagration. Consistent with earlier work, these realizations produce the familiar hot dense bound remnant surrounded by sparse ejecta. Our results indicate that the majority of the star remains unburned (∼70%) and bound (>90%). Our realizations produce total ejecta yields on the order of 10⁻²–10⁻¹M_☉, ejected⁵⁶Ni yields on the order of 10⁻⁴–10⁻²M_☉, and ejecta kinetic energies on the order of 10⁴⁸–10⁴⁹erg. Compared to yields inferred from recent observations of the dimmest Type Iax events—SN 2007qd, SN 2008ha, SN 2010ae, SN 2019gsc, SN 2019muj, SN 2020kyg, and SN 2021fcg—our simulation produces comparable⁵⁶Ni yields but too-small total yields and kinetic energies. Reignition of the remnant is also seen in some realizations. 

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2. Seismic Signatures of the ¹² C(α, γ) ¹⁶ O Reaction Rate in White Dwarf Models with Overshooting

   https://doi.org/10.3847/1538-4357/ace620  

   Chidester, Morgan T; Timmes, F X; Farag, Ebraheem (August 2023, The Astrophysical Journal)

   Abstract We consider the combined effects that overshooting and the¹²C(α,γ)¹⁶O reaction rate have on variable white dwarf (WD) stellar models. We find that carbon–oxygen (CO) WD models continue to yield pulsation signatures of the current experimental¹²C(α,γ)¹⁶O reaction rate probability distribution function when overshooting is included in the evolution. These signatures hold because the resonating mantle region, encompassing ≃0.2M_⊙in a typical ≃0.6M_⊙WD model, still undergoes radiative helium burning during the evolution to a WD. Our specific models show two potential low-order adiabatic g-modes,g₂andg₆, that signalize the¹²C(α,γ)¹⁶O reaction rate probability distribution function. Both g-mode signatures induce average relative period shifts of ΔP/P= 0.44% and ΔP/P= 1.33% forg₂andg₆, respectively. We find thatg₆is a trapped mode, and theg₂period signature is inversely proportional to the¹²C(α,γ)¹⁶O reaction rate. Theg₆period signature generally separates the slower and faster reaction rates, and has a maximum relative period shift of ΔP/P= 3.45%. We conclude that low-order g-mode periods from CO WDs may still serve as viable probes for the¹²C(α,γ)¹⁶O reaction rate probability distribution function when overshooting is included in the evolution. 

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3. Type C blocks of super category $$\mathcal {O}$$ O

   https://doi.org/10.1007/s00209-019-02400-y  

   Brundan, Jonathan; Davidson, Nicholas (December 2019, Mathematische Zeitschrift)
4. On Trapped Modes in Variable White Dwarfs as Probes of the ¹² C(α, γ) ¹⁶ O Reaction Rate

   https://doi.org/10.3847/1538-4357/ac7ec3  

   Chidester, Morgan T.; Farag, Ebraheem; Timmes, F. X. (August 2022, The Astrophysical Journal)

   Abstract We seek signatures of the current experimental 12 C α , γ 16 O reaction rate probability distribution function in the pulsation periods of carbon–oxygen white dwarf (WD) models. We find that adiabatic g-modes trapped by the interior carbon-rich layer offer potentially useful signatures of this reaction rate probability distribution function. Probing the carbon-rich region is relevant because it forms during the evolution of low-mass stars under radiative helium-burning conditions, mitigating the impact of convective mixing processes. We make direct quantitative connections between the pulsation periods of the identified trapped g-modes in variable WD models and the current experimental 12 C α , γ 16 O reaction rate probability distribution function. We find an average spread in relative period shifts of Δ P / P ≃ ±2% for the identified trapped g-modes over the ±3 σ uncertainty in the 12 C α , γ 16 O reaction rate probability distribution function—across the effective temperature range of observed DAV and DBV WDs and for different WD masses, helium shell masses, and hydrogen shell masses. The g-mode pulsation periods of observed WDs are typically given to six to seven significant figures of precision. This suggests that an astrophysical constraint on the 12 C α , γ 16 O reaction rate could, in principle, be extractable from the period spectrum of observed variable WDs. 

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5. π-Bond Dissociation Energies: C–C, C–N, and C–O

   https://doi.org/10.1021/acs.joc.4c01925  

   Kass, Steven R (October 2024, The Journal of Organic Chemistry)