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arXiv 1503.07494astro-ph.SR
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主序星II上的恒星风：自转和风的演化

Stellar Winds on the Main-Sequence II: the Evolution of Rotation and Winds

C. P. Johnstone, M. Güdel, I. Brott, T. Lüftinger

备注：
26 pages, 14 figures, 2 tables, to be published in A&A
发表信息：
A&A 577, A28 (2015)
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摘要：

目的：研究低质量主序星自转和风性质的演化。我们的目标是使用旋转演化模型来约束恒星风的质量损失率，并预测它们的性质如何随主序星的时间演化。方法：利用观测到的年轻星团的自转分布，建立一个自转演化模型。拟合我们模型中的自由参数使我们能够预测风质量损失率如何取决于恒星质量，半径和旋转。我们将结果与本系列论文I中开发的风模型相结合，以预测风特性如何在主序列上演变。结果：我们估计风的质量损失率与恒星参数的标度为$\dot{M}_\star \propto R_\star^2 Ω_\star^{1.33} M_\star^{-3.36}$。我们估计，在年轻的时候，太阳风的质量损失率可能比现在的太阳风高一个数量级。这导致风在年轻时具有更高的密度;然而，这种变化的幅度在很大程度上取决于我们如何衡量风的温度。由于自转速率的分散，年轻恒星在给定的年龄表现出大范围的风特性。随着恒星年龄的增长，风的性质的这种扩散消失了。结论：我们对主序星风演化的认识存在很大的不确定性，这是由于我们对恒星风的认识不足，以及年轻时自转速率的巨大差异。鉴于行星大气对恒星风和辐射条件的敏感性，这些不确定性对我们理解行星环境的演变具有重要意义。

英文摘要：

Aims: We study the evolution of stellar rotation and wind properties for low-mass main-sequence stars. Our aim is to use rotational evolution models to constrain the mass loss rates in stellar winds and to predict how their properties evolve with time on the main-sequence. Methods: We construct a rotational evolution model that is driven by observed rotational distributions of young stellar clusters. Fitting the free parameters in our model allows us to predict how wind mass loss rate depends on stellar mass, radius, and rotation. We couple the results to the wind model developed in Paper I of this series to predict how wind properties evolve on the main-sequence. Results: We estimate that wind mass loss rate scales with stellar parameters as $\dot{M}_\star \propto R_\star^2 Ω_\star^{1.33} M_\star^{-3.36}$. We estimate that at young ages, the solar wind likely had a mass loss rate that is an order of magnitude higher than that of the current solar wind. This leads to the wind having a higher density at younger ages; however, the magnitude of this change depends strongly on how we scale wind temperature. Due to the spread in rotation rates, young stars show a large range of wind properties at a given age. This spread in wind properties disappears as the stars age. Conclusions: There is a large uncertainty in our knowledge of the evolution of stellar winds on the main-sequence, due both to our lack of knowledge of stellar winds and the large spread in rotation rates at young ages. Given the sensitivity of planetary atmospheres to stellar wind and radiation conditions, these uncertainties can be significant for our understanding of the evolution of planetary environments.

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