磁化旋转白矮星吸积诱导坍缩中的核合成
Nucleosynthesis in the Accretion-induced Collapse of magnetised, Rotating White Dwarfs
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中文总结 AI 辅助
该研究通过三维广义相对论模拟结合核网络，发现磁化旋转白矮星吸积诱导坍缩事件可产生弱r-过程核，其⁵⁶Ni产额低于核心坍缩超新星，重元素 ejecta集中在赤道至中纬度区域。
中文摘要 AI 辅助
旋转氧氖镁白矮星（WD）的吸积诱导坍缩（AIC）是中子星形成的替代通道，即接近钱德拉塞卡质量的吸积恒星发生坍缩而非热核瓦解。若前身白矮星磁化程度足够，可驱动类似磁旋转超新星的磁旋转外流，或成为快速中子俘获（r-过程）核合成的场所。我们利用WinNet核反应网络，对5个三维广义相对论中微子（磁）流体动力学AIC模拟中的示踪粒子进行后处理，这些模拟涵盖4种初始自转速率。 ejecta质量、达到核统计平衡的物质占比、铁族以外的 ejecta质量均随自转速率单调增加，磁场会放大这些趋势。自转最慢的模型仅合成铁族物质，自转最快且磁化最强的模型则达到质量数A≈130的第二r-过程丰度峰，并有微量、强度较低的信号延伸至A≈244。对应的⁵⁶Ni质量从0.007M⊙升至0.014M⊙，比核心坍缩超新星和超新星的典型产额低5至40倍以上，意味着放射性驱动成分相应较暗。与磁旋转驱动超新星的图像相反，最重的 ejecta并不沿极向外流分布，而是位于赤道至中纬度的中等熵瓣中，极区柱本身是某些重元素的局部最小值。我们得出结论：快速旋转、磁化的AIC事件可能贡献银河系铁以外元素和弱r-过程核的产额，但所有模型均未产生可靠的第三r-过程峰。
英文摘要
Accretion-induced collapse (AIC) of a rotating oxygen-neon-magnesium white dwarf (WD) is an alternative channel of neutron-star formation, in which a mass-accreting star near the Chandrasekhar mass collapses instead of being disrupted thermonuclearly. If the progenitor WD is sufficiently magnetised, it can drive magnetorotational outflows analogous to those of magnetorotational supernovae and may serve as a site for rapid neutron-capture ($r$-process) nucleosynthesis. We post-process tracer particles from five three-dimensional general-relativistic neutrino-(magneto)hydrodynamic AIC simulations, spanning four initial rotation rates, with the WinNet nuclear reaction network. Ejecta mass, the fraction of matter reaching nuclear statistical equilibrium, and the mass ejected beyond the iron group all increase monotonically with rotation rate, with magnetic fields amplifying these trends. The slowest-rotating model synthesises essentially only iron-group material, while the most rapidly rotating and magnetised model reaches the second $r$-process abundance peak at mass number $A \approx 130$, with a trace, non-robust signal up to $A \approx 244$. The corresponding $^{56}$Ni mass rises from $0.007$ to $0.014 M_\odot$, lower than representative yields for core-collapse supernovae and hypernovae by factors of five to more than forty, implying a correspondingly faint radioactively powered component. Contrary to the picture established for magnetorotationally driven supernovae, the heaviest ejecta do not track the polar outflow: they instead reside in equatorial-to-mid-latitude, moderate-entropy lobes, while the polar column is itself a local minimum in some heavy elements. We conclude that rapidly rotating, magnetised AIC events could contribute to the Galactic yields of trans-iron and weak $r$-process nuclei, although none of our models produces a robust third $r$-process peak.
