Title: The SPAr process: proton captures powering carbon-oxygen shell mergers in massive stars Show Chinese title

Title: SPAr过程：大质量恒星中碳氧壳层合并的质子捕获

Abstract: Carbon-oxygen (C-O) shell mergers in massive stars play a crucial role in both nucleosynthesis and the final stages of stellar evolution. These convective-reactive events significantly alter the internal structure of the star shortly before core collapse. We investigate how the enhanced production of light particles (especially protons) during a C-O shell merger, relative to classical oxygen shell burning, affects the energy balance and evolution of the convective shell. We derive the budget for direct and reverse nucleosynthesis flows across all relevant nuclear reactions from stellar evolution models, and we assess the relative energy produced. We find that proton capture reactions on 32,34S, 31P, and 38Ar (SPAr) dominate the nuclear energy production in typical C-O shell mergers as predicted by 1D stellar models. Their combined energy output is approximately 400 times greater than that of C and O fusion under the same conditions. Our results highlight the critical importance of including these proton-capture reactions in simulations of convective-reactive burning. Excluding their contribution can lead to inaccurate modeling of the dynamics and nucleosynthesis in advanced stellar evolutionary phases. Such results will need to be confirmed by 3D hydrodynamics models. Show Chinese abstract

Abstract: 碳-氧（C-O）外壳合并在大质量恒星中在核合成和恒星演化的最后阶段起着关键作用。 这些对流-反应事件在核心坍缩前显著改变恒星的内部结构。 我们研究了在C-O外壳合并期间，相对于经典的氧外壳燃烧，轻粒子（尤其是质子）的增强产生如何影响对流外壳的能量平衡和演化。 我们从恒星演化模型中推导出所有相关核反应的直接和逆向核合成流量的预算，并评估了相对产生的能量。 我们发现，在1D恒星模型预测的典型C-O外壳合并中，32,34S、31P和38Ar（SPAr）上的质子捕获反应主导了核能产生。 它们的总能量输出大约是相同条件下C和O融合的400倍。 我们的结果突显了在对流-反应燃烧模拟中包含这些质子捕获反应的关键重要性。 排除它们的贡献可能导致对高级恒星演化阶段的动力学和核合成的不准确建模。 这样的结果需要通过3D流体动力学模型来确认。