低质量恒星中半径依赖的Angular Momentum演化。I
Radius Dependent Angular Momentum Evolution in Low-Mass Stars. I
摘要：
低质量恒星的角动量演化取决于恒星形成的初始条件、恒星结构演化和恒星磁场的行为。在这里，我们表明，角动量演化的经验图片自然出现，如果旋转有关的磁场强度，而不是磁通量，并制定了一个修正的制动定律的基础上。角动量演化成为恒星半径的一个强函数，解释了在疏散星团和场星中观察到的几个Gyr的主要趋势：在边界处旋转到完全对流的急剧过渡主要来自于穿过这个边界的半径的大变化，并且不需要发电机模式或场拓扑的变化。此外，这些数据表明，太阳型恒星之间存在瞬时的核心-包络解耦，而在极低质量恒星中，磁场饱和的周期更长。对于太阳型恒星，我们的模型也符合经验Skumanich定律。最后，在进一步支持的理论，我们表明，在我们的模型中，低质量恒星自旋从饱和到不饱和的领域制度的预测年龄对应的非常好，在这些恒星的磁活动的观察寿命。
英文摘要：
Angular momentum evolution in low-mass stars is determined by initial conditions during star formation, stellar structure evolution, and the behaviour of stellar magnetic fields. Here we show that the empirical picture of angular momentum evolution arises naturally if rotation is related to magnetic field strength instead of to magnetic flux, and formulate a corrected braking law based on this. Angular momentum evolution then becomes a strong function of stellar radius, explaining the main trends observed in open clusters and field stars at a few Gyr: the steep transition in rotation at the boundary to full convection arises primarily from the large change in radius across this boundary, and does not require changes in dynamo mode or field topology. Additionally, the data suggest transient core-envelope decoupling among solar-type stars, and field saturation at longer periods in very low-mass stars. For solar-type stars, our model is also in good agreement with the empirical Skumanich law. Finally, in further support of the theory, we show that the predicted age at which low-mass stars spin down from the saturated to unsaturated field regimes in our model corresponds remarkably well to the observed lifetime of magnetic activity in these stars.
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