发表机构
University of Victoria; University of Minnesota（维多利亚大学; 明尼苏达大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过三维模拟揭示大质量恒星深内部对流壳层边界处内重力波在$N^2$峰值引起高效混合，侵蚀熵梯度，影响超新星可爆炸性预测，并可能促进壳层合并。
AI 中文摘要
对流边界混合的物理涉及穿透和过冲等概念，并且主要针对包层和核心对流进行了表征。对于大质量恒星在其最后阶段深处的燃烧壳层，对流边界仍然知之甚少。一维恒星演化代码通常在下对流壳层边界处放置陡峭的熵梯度以及相应的窄 \brunt{}（$N^2$）峰值。基于对核心坍缩前11天的 $25 \rm{M_\bullet}$ 恒星的高分辨率三维流体动力学模拟，我们发现对流在代表C壳层对流底部的 $N^2$ 峰值处激发高频内重力波。这些波有效地混合熵和物质，$N^2$ 峰值在数小时内被侵蚀约40%，相应地减少了熵梯度。在数值收敛的模拟中，$N^2$ 峰值处的波驱动扩散系数为 $D\thickapprox 5\text{--}6\times 10^{9} \rm{cm}^2 \rm{second}^{-1}$。我们的模拟表明，该边界处的主要物理是内重力波引起的混合。利用三维模拟中随时间变化的 $D$ 系数进行外推，峰值处的熵阶跃在半天内减少40--85%，从而减少了密度、温度和熵梯度，这些梯度决定了停滞的超新星激波所遇到的吸积率下降。这种物理未包含在当今的一维模型中，并进入预测可爆炸性的结构参数中。在坍缩前几天使梯度变平有利于O--C壳层合并，这可能重塑坍缩前的核合成。没有这种物理，一维模型携带过于陡峭的梯度，从而在可爆炸性调查、产额表以及基于它们的化学演化研究中引入了先前未考虑的系统误差。
英文摘要
The physics of convective boundary mixing involves concepts such as penetration and overshooting and has been mostly characterized for envelope and core convection. For the burning shells deep inside massive stars in their final stages, the convective boundary remains poorly understood. 1D stellar-evolution codes typically place a steep entropy gradient and the corresponding narrow \brunt{} ($N^2$) peak at a lower convective shell boundary. Based on high-resolution 3D hydrodynamic simulations of a $25 \rm{M_\odot}$ star 11 days before core collapse, we find that convection excites high-frequency internal gravity waves at the $N^2$ peak representing the C-shell convection bottom. These waves efficiently mix entropy and species and the $N^2$ peak erodes by ${\sim}40\%$ within hours, correspondingly reducing the entropy gradient. The wave-driven diffusion coefficient is $D\approx 5\text{--}6\times 10^{9} \rm{cm}^2 \rm{second}^{-1}$ at the $N^2$ peak in numerically converged simulations. Our simulations show that the dominant physics at this boundary is mixing due to internal gravity waves. Extrapolated with the time-dependent $D$ coefficient from the 3D simulations, the entropy step across the peak decreases by 40--85\% within half a day, thereby reducing the density, temperature and entropy gradients that set the accretion-rate drop a stalled supernova shock encounters. This physics is not included in present-day 1D models and enters the structural parameters that predict explodability. Flattening the gradients days before collapse favors an O--C shell merger, which could reshape pre-collapse nucleosynthesis. Without this physics 1D models carry too sharp gradients that introduce previously unaccounted systematic errors into the explodability surveys, yield tables and chemical-evolution studies built on them.
CommentsSubmitted to ApJL
