arXiv 2301.026042023-01-06astro-ph.SR

基于二维流体动力学模拟的对流核过冲作为恒星质量函数的研究

A study of convective core overshooting as a function of stellar mass based on two-dimensional hydrodynamical simulations

I. Baraffe, J. Clarke, A. Morison, D. G. Vlaykov, T. Constantino, T. Goffrey, T. Guillet, A. Le Saux, J. Pratt

备注：: 13 pages, accepted for publication in MNRAS
DOI：: 10.1093/mnras/stad009

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摘要：

本文对质量范围从3 $M_\odot$到20 $M_\odot$的零年龄主序星的核心对流进行了二维数值模拟。用完全可压缩的时间隐式码MUSIC进行了仿真。我们研究了过冲的效率，它描述了穿越对流边界的对流流的弹道过程，作为恒星质量和光度的函数。我们还研究了人为增加恒星光度对3个$M_\odot$模型的影响。模拟涵盖数百至数千对流周转时间尺度。应用框架的极端羽流事件以前开发的对流信封，我们得到过冲长度作为恒星质量的函数。我们发现超调距离（$d_{\rm ov}$）与恒星光度（$L$）和对流核心半径（$r_{\rm conv}$）成正比。我们推导了一个标度律$d_{\rm ov} \propto L^{1/3} r_{\rm conv}^{1/2}$，它是在一个1D恒星演化代码和由此产生的恒星模型进行了比较，观察。缩放预测的超调距离，显着增加恒星质量的值，在定性与观测一致。然而，在定量上，预测值被低估的群众$\gtrsim 10 M_\odot$。我们的二维模拟显示，形成一个接近绝热层的史瓦西边界的对流核心，在最近的三维模拟对流。最明亮的模型显示了近绝热层的尺寸随时间的增长。随着近绝热层的上边缘越来越接近最大过冲长度，并且随着模拟时间超过过冲层中的典型热扩散时间尺度，这种增长似乎会减慢。

英文摘要：

We perform two-dimensional numerical simulations of core convection for zero-age-main-sequence stars covering a mass range from 3 $M_\odot$ to 20 $M_\odot$. The simulations are performed with the fully compressible time-implicit code MUSIC. We study the efficiency of overshooting, which describes the ballistic process of convective flows crossing a convective boundary, as a function of stellar mass and luminosity. We also study the impact of artificially increasing the stellar luminosity for 3 $M_\odot$ models. The simulations cover hundreds to thousands of convective turnover timescales. Applying the framework of extreme plume events previously developed for convective envelopes, we derive overshooting lengths as a function of stellar masses. We find that the overshooting distance ($d_{\rm ov}$) scales with the stellar luminosity ($L$) and the convective core radius ($r_{\rm conv}$). We derive a scaling law $d_{\rm ov} \propto L^{1/3} r_{\rm conv}^{1/2}$ which is implemented in a 1D stellar evolution code and the resulting stellar models are compared to observations. The scaling predicts values for the overshooting distance that significantly increase with stellar mass, in qualitative agreement with observations. Quantitatively, however, the predicted values are underestimated for masses $\gtrsim 10 M_\odot$. Our 2D simulations show the formation of a nearly-adiabatic layer just above the Schwarzschild boundary of the convective core, as exhibited in recent 3D simulations of convection. The most luminous models show a growth in size with time of the nearly-adiabatic layer. This growth seems to slow down as the upper edge of the nearly-adiabatic layer gets closer to the maximum overshooting length and as the simulation time exceeds the typical thermal diffusive timescale in the overshooting layer.

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