Numerical Simulations of Convective Three-dimensional Red Supergiant Envelopes
Numerical Simulations of Convective Three-dimensional Red Supergiant Envelopes
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DOI：
10.3847/1538-4357/ac5ab3
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发表时间：
2021-10
期刊：
影响因子：
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通讯作者：
J. A. Goldberg;Y. Jiang 姜;L. Bildsten
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文献类型：
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作者：
J. A. Goldberg;Y. Jiang 姜;L. Bildsten
我们探索的对流，发光（L <$104.5 -105 L <$），富氢信封的红超巨星（RSG）的三维性质的基础上使用雅典娜++在球面几何的辐射流体动力学模拟。这些计算包含了恒星体积的30%，包括气体和辐射压力，并自洽地跟踪模拟的M 15 M恒星的外部M 3 M的引力势。这项工作揭示了一个半径，R corr，周围的对流性质的变化。对于r > R corr，尽管仍然是光学厚的，光子的扩散主导能量传输。这种机制在亮度较低的恒星中得到了很好的研究，但在RSG中，接近（或高于）爱丁顿光度（由于电离跃迁时的不透明度增强）导致密度较高的区域向外移动而不是向内移动。这一区域的星星也有大量的湍流压力，产生的密度结构比一维恒星演化预测的要大得多。这种物质的“晕”将影响对IIP型超新星的冲击爆发和早期光变曲线的预测。在R corr内部，我们发现了一个近似平坦的熵分布，正如混合长度理论（MLT）的有效区域所预期的那样。辐射压力提供了该区域中对抗重力的三分之一的支持。我们与MLT的比较表明，混合长度为α = 3-4，与模拟中看到的对流羽流的大小一致。这些三维模型的时间变化主要是对流羽流的寿命（约300天）的时间尺度上，与光度观测到的振幅一致。
We explore the three-dimensional properties of convective, luminous (L ≈ 104.5–105 L ⊙), hydrogen-rich envelopes of red supergiants (RSGs) based on radiation hydrodynamic simulations in spherical geometry using Athena++. These computations comprise ≈30% of the stellar volume, include gas and radiation pressure, and self-consistently track the gravitational potential for the outer ≈3M ⊙ of the simulated M ≈ 15M ⊙ stars. This work reveals a radius, R corr, around which the nature of the convection changes. For r > R corr, though still optically thick, diffusion of photons dominates the energy transport. Such a regime is well studied in less luminous stars, but in RSGs, the near- (or above-)Eddington luminosity (due to opacity enhancements at ionization transitions) leads to the unusual outcome of denser regions moving outward rather than inward. This region of the star also has a large amount of turbulent pressure, yielding a density structure much more extended than 1D stellar evolution predicts. This “halo” of material will impact predictions for both shock breakout and early lightcurves of Type IIP supernovae. Inside of R corr, we find a nearly flat entropy profile as expected in the efficient regime of mixing-length theory (MLT). Radiation pressure provides ≈1/3 of the support against gravity in this region. Our comparisons to MLT suggest a mixing length of α = 3–4, consistent with the sizes of convective plumes seen in the simulations. The temporal variability of these 3D models is mostly on the timescale of the convective plume lifetimes (≈300 days), with amplitudes consistent with those observed photometrically.