arXiv 2003.020942020-03-04astro-ph.SR

行星状星云中心恒星的星风模型

Stellar wind models of central stars of planetary nebulae

J. Krticka, J. Kubat, I. Krtickova

备注：: 14 pages, accepted for publication in Astronomy & Astrophysics
发表信息：: A&A 635, A173 (2020)
DOI：: 10.1051/0004-6361/201937150

摘要：

快速线驱动的恒星风在行星状星云的演化过程中起着重要的作用。我们提供了行星状星云中心恒星的全球热星风模型。该模型预测风的结构，包括质量损失率，终极速度，和从基本恒星参数的出射通量。我们应用我们的风代码的参数对应的渐近巨星分支和白矮星阶段之间的演化阶段。我们研究了金属丰度和风的不均匀性（聚集）对风的性质的影响。线驱动风在恒星离开渐近巨星分支后很早就出现（最迟为$T_\rm{eff}\approx10\,$ kK），并在白矮星冷却轨道（低于$T_\rm{eff}=105\,$ kK）逐渐消失。它们的质量损失率主要与恒星的光度成正比，因此，在赫兹斯普朗-拉塞尔图从红色部分到蓝色部分的过渡期间，质量损失率仅略有变化。有以下两个例外的单调行为：在$20\,$ kK附近的双稳态跳跃，其中质量损失率减少了几个因素（在进化过程中）由于铁离子化的变化，和一个额外的最大值约为$T_\rm{eff}=40-50\,$ kK。另一方面，由于恒星半径减小，在过渡期间，终极速度从大约几百个$\rm{km}\,\rm{s}^{-1}$增加到几千个$\rm{km}\,\rm{s}^{-1}$。风的终极速度也显着增加在双稳态跳跃。导出的风参数与观测值吻合较好。团簇效应在双稳态跃迁的热端比冷端强。导出的风参数拟合可用于演化模型和行星状星云形成的研究。预测的质量损失率的双稳态跳跃可能会导致行星状星云的额外外壳的出现。

英文摘要：

Fast line-driven stellar winds play an important role in the evolution of planetary nebulae. We provide global hot star wind models of central stars of planetary nebulae. The models predict wind structure including the mass-loss rates, terminal velocities, and emergent fluxes from basic stellar parameters. We applied our wind code for parameters corresponding to evolutionary stages between the asymptotic giant branch and white dwarf phases. We study the influence of metallicity and wind inhomogeneities (clumping) on the wind properties. Line-driven winds appear very early after the star leaves the asymptotic giant branch (at the latest for $T_\rm{eff}\approx10\,$kK) and fade away at the white dwarf cooling track (below $T_\rm{eff}=105\,$kK). Their mass-loss rate mostly scales with the stellar luminosity and, consequently, the mass-loss rate only varies slightly during the transition from the red to the blue part of the Hertzsprung-Russell diagram. There are the following two exceptions to the monotonic behavior: a bistability jump at around $20\,$kK, where the mass-loss rate decreases by a factor of a few (during evolution) due to a change in iron ionization, and an additional maximum at about $T_\rm{eff}=40-50\,$kK. On the other hand, the terminal velocity increases from about a few hundreds of $\rm{km}\,\rm{s}^{-1}$ to a few thousands of $\rm{km}\,\rm{s}^{-1}$ during the transition as a result of stellar radius decrease. The wind terminal velocity also significantly increases at the bistability jump. Derived wind parameters reasonably agree with observations. The effect of clumping is stronger at the hot side of the bistability jump than at the cool side. Derived fits to wind parameters can be used in evolutionary models and in studies of planetary nebula formation. A predicted bistability jump in mass-loss rates can cause the appearance of an additional shell of planetary nebula.

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