AI 中文总结
本研究验证了复合驱动恒星风的可能性，在CASTRO代码中实现含复合加热项的帕克风模型，发现其可驱动稳定外流，指出演化红巨星和AGB星或存在此类风。
AI 中文摘要
低温恒星大气中，中性氢的数量随高度增加而显著增多，这表明当远离恒星深层光球层时，氢会发生复合。复合过程有可能驱动恒星风，尤其是在低温且演化后的恒星中。本研究旨在验证复合驱动恒星风的可能性，并构建这类风驱动的初始模型。我们通过将每个原子的引力势能与氢电离能进行比较，在赫罗图（HR diagram）范围内研究复合驱动外流的可能性。随后，我们从一个简单的解析模型出发，在帕克风（Parker wind）模型的气体中添加额外的加热项，该加热项模拟复合过程释放的热量，以此研究其如何驱动外流。我们在CASTRO代码中实现了该模型，并检验了解的流体动力学稳定性。当用渐近巨星分支（AGB）星的参数进行测试时，添加的加热项在我们的模型中驱动了稳定的跨声速外流；加热函数会影响解的形态，且声点的位置取决于加热函数自身的位置。尽管推导的流体动力学方程与密度无关，但我们确定了决定质量损失率的过程。通过对比碰撞复合产生的加热与辐射复合导致的冷却，我们发现需要相对较高的密度才能将复合能量以热量形式释放，这意味着质量损失率约为0.1倍太阳质量每年。我们在赫罗图上的能量对比表明，演化后的红巨星和AGB星中存在复合驱动风的可能性，而恒星大气中复合释放热量的径向分布是驱动风的主要决定因素，进而会影响质量损失率。
英文摘要
Low-temperature stars have a significant population of neutral hydrogen increasing with height in their atmospheres. This suggests eventual recombination as we move away from their deep photospheric layers. Recombination can potentially drive stellar winds, particularly in cool and evolved stars. We aim to verify the possibility of stellar winds driven by recombination. We also aim to constitute an initial model for this type wind driving. We examine the possibility of recombination-driven outflows across the HR diagram by comparing the gravitational potential energy per atom to the hydrogen ionization energy. Then we start from a simple analytical model with the addition of an extra heating term to the gas in the Parker wind model. We model the heating term, analogous to the heat released by recombination, and examine how it can drive an outflow. We implement the model in the code CASTRO and check the hydrodynamic stability of the solution. The added heating drives a steady transonic outflow in our models, when tested with the parameters of an AGB star. The heating function affects the solution and the location of the sonic point depends on the location of the heating function itself. Even though the derived hydrodynamic equations are independent of the density, we determine the processes that set the mass-loss rate. By comparing the heating from collisional recombination and cooling due to radiative recombination, we show that relatively high densities are required to release the recombination energy as heat, implying mass-loss rates of the order of 0.1 solar mass per year. Our comparison of energies across the HR diagram suggests a possibility of recombination-driven winds in evolved red giants and AGB stars. The main deciding factor for wind launching is the radial distribution of heat released by recombination in a star's atmosphere. This can in turn affect the mass-loss rate.
CommentsSubmitted to A&A, 11 pages, 6 figures
