AF And 的研究 I. 热态氢丰度约束与动力学一致风模型
The study of AF And. I. Hydrogen abundance constraints and dynamically-consistent wind model of the hot state
- Special Astrophysical Observatory（特别天文台）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
本文通过 CMFGEN 非LTE建模和动力学一致速度场，约束了M31中亮蓝变星AF And热态的氢丰度（20%-30%）及当前质量（15.6-17.7 M⊙），并估计初始质量约50 M⊙。
AI中文摘要：
本文开启了一系列致力于深入研究中仙女座星系（M31）中的亮蓝变星 AF And 的工作。我们在此展示了使用 CMFGEN 代码对该星在热态下进行非局部热动平衡（non-LTE）建模的结果。除了在恒星大气分析中广泛使用的 $\beta$ 速度律外，我们还使用了由风中径向力平衡（包括若干模型中的离心力）获得的速度分布。这种动力学一致的方法在建模过程中减少了参数空间，此外还使我们能够估算当前恒星质量，其内部静水力学层被致密的风所遮蔽，而风污染了吸收谱线。基于我们的建模，我们估算 AF And 的参数如下：光度 $L \approx 6.5\times10^5~\text{L}_\odot$，质量损失率 $\dot{M} \approx 3\times10^{-5}~\text{M}_\odot~\text{yr}^{-1}$，终端速度 $v_\infty \approx 300~\text{km s}^{-1}$，有效温度 $T_{\rm eff} \approx 17~\text{kK}$。对 AF And 热态的建模特别令人感兴趣，因为有可能对氢和氦丰度之比施加约束，以便进一步用于构建该星的冷态模型。我们得出结论，当前风中的氢质量分数在 20% 到 30% 之间。自洽建模给出的当前质量 $M_*$ 估计在 $15.6 - 17.7~\text{M}_\odot$ 范围内。通过采用演化轨迹，我们能够估算初始恒星质量为 $M_{*,~init} \approx 50~\text{M}_\odot$。
英文摘要：
This paper starts a series of works devoted to an in-depth study of luminous blue variable AF And in the M31 galaxy. Here we present the results of non-LTE modelling of the star in a hot state with CMFGEN code. In addition to the $β$-velocity law, widely used in the analysis of stellar atmospheres, we used a velocity distribution obtained from the balance of radial forces in the wind, including centrifugal forces for several models. Such a dynamically consistent approach reduces the parameter space during modelling and, in addition, allows us to estimate the current stellar mass whose inner hydrostatic layers are obscured by a dense wind that contaminates the absorption profiles. Based on our modelling we estimate the parameters of AF And as follows: luminosity $L \approx 6.5\times10^5~\text{L}_\odot$, mass loss rate $\dot{M}$ $\approx 3\times10^{-5}~\text{M}_\odot~\text{yr}^{-1}$, terminal velocity $v_\infty \approx 300~\text{km s}^{-1}$ and effective temperature $T_{\rm eff} \approx 17~\text{kK}$. modelling of the hot state of AF And is of particular interest due to the possibility to place constraints on the ratio of hydrogen and helium abundances for further use in constructing models of the cold state of this star. We conclude that the current hydrogen mass fraction in the wind lies in the range from $20$ to $30$ per cent. Self-consistent modelling gives the current mass $M_*$ estimation in the range $15.6 - 17.7~\text{M}_\odot$. By employing evolutionary tracks, we were able to estimate the initial stellar mass as $M_{*,~init} \approx 50~\text{M}_\odot$.
