坍缩星盘外流 I：轴对称中的黏性流体动力学演化
Collapsar disk outflows I: Viscous hydrodynamic evolution in axisymmetry
AI总结：
本研究通过轴对称黏性流体动力学模拟，研究快速旋转沃尔夫-拉叶星坍缩形成的吸积盘外流，发现其不足以产生r-过程元素，但可产生$^{56}$Ni驱动Ic-BL超新星，并指出中微子发射特征可作为前身星内部条件的观测诊断。
摘要：
我们研究了快速旋转的沃尔夫-拉叶星坍缩过程中形成的吸积盘的质量抛射。在恒星中心形成的由中微子冷却的黑洞（BH）吸积盘系统——以及随后产生的外流——为这些系统成为候选的r-过程元素产生位点和宽谱Ic型（Ic-BL）超新星的潜在前身星提供了条件。在此，我们展示了坍缩星盘的全局、长期轴对称流体动力学模拟，其中包括通过剪切黏度进行的角动量输运、中微子发射与吸收、包含19种同位素的核反应网络和核统计平衡求解器、一个质量与自旋随吸积物质修改的赝牛顿BH，以及自引力。从球对称坍缩的恒星轮廓出发，我们的模型自洽地捕获了盘的形成，并演化至盘风驱动的激波到达恒星表面之后。我们的所有模型均未达到足够的中子化程度以抛射显著的r-过程元素（详细的核合成计算将在后续论文中给出）。产生了足够的$^{56}$Ni以驱动典型的Ic-BL超新星光变曲线，但平均渐近速度比典型Ic-BL超新星光谱中的线宽所对应的速度慢约2-3倍。BH形成与激波盘形成之间的中微子发射间隙，以及随后发射峰值的幅度，将是银河系坍缩星中前身星内部条件的可观测诊断特征。激波盘在膨胀之前的周期性振荡也可能通过其对中微子和引力波信号的影响而成为可观测特征。
英文摘要：
We investigate mass ejection from accretion disks formed during the collapse of rapidly-rotating Wolf-Rayet stars. The neutrino-cooled, black hole (BH) accretion disk system that forms at the center of the star -- and the ensuing outflows -- provide the conditions for these systems to be candidate $r$-process element production sites and potential progenitors of broad-lined Type Ic (Ic-BL) supernovae. Here we present global, long-term axisymmetric hydrodynamic simulations of collapsar disks that include angular momentum transport through shear viscosity, neutrino emission and absorption, a 19-isotope nuclear reaction network and nuclear statistical equilibrium solver, a pseudo-Newtonian BH with mass and spin modified by accreted matter, and self-gravity. Starting from a stellar profile collapsed in spherical symmetry, our models capture disk formation self-consistently, and are evolved until after the shock wave -- driven by disk winds -- reaches the surface of the star. None of our models achieve sufficient neutronization to eject significant amounts of $r$-process elements (detailed nucleosynthesis calculations will follow in a companion paper). Sufficient $^{56}$Ni is produced to power a typical type Ic-BL supernova light curve, but the average asymptotic velocity is a factor $\sim 2-3$ times too slow to account for the typical line widths in type Ic-BL supernova spectra. The gap in neutrino emission between BH formation and shocked disk formation, and the magnitude of the subsequent peak in emission, would be observable diagnostics of the internal conditions of the progenitor in a galactic collapsar. Periodic oscillations of the shocked disk prior to its expansion are also a potential observable through their impact on the the neutrino and gravitational wave signals.
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