The rotational evolution of low-mass stars

冷恒星演化过程中的一个重要方面是它们的自转。已经发展起来的理论模型对自转如何随质量和年龄变化做出了明确和可检验的预测。然而，一些物理效应已经被添加到模型中，而不知道它们是否必要，或者可以通过观测进行测试。这涉及，除其他事项外，差分旋转与固体模型，磁盘（或行星）锁定，和磁饱和。通过非常精确地测量恒星的旋转，没有混叠和其他非唯一性，例如，v sin i已经影响了先前的数据，作为恒星质量/颜色的函数和恒星年龄的函数，这些观测将简单地消除模型的波动空间，并根据经验指定恒星的旋转演化。因此，这些观测结果的有用性超出了对任何理论模型的检验。事实上，我们的调查可能会导致重新评估模型中哪些是（不）必要的。因此，我们建议通过精确的时间序列CCD测光，确定12个年龄在5000万年到1.5 Gyr之间的邻近疏散星团中的低质量（中F、G、K和早期M型）恒星的大量（≥ 1，000）自转周期。在这次巡天的最后，也就是STELLA疏散星团巡天，我们将清楚地知道FGKM恒星的主序星旋转演化是年龄的函数。观测确定的依赖关系的细节然后可以用于理解全局依赖关系。然后，理论模型将被剥离到最基本的东西，然后重建以符合观察结果，去除多余的影响并识别新的依赖关系。

An important aspect in the evolutionary scenario of cool stars is their rotation. Theoretical models already developed make definite and testable predictions of how rotation changes with mass and age. However, a number of physical effects have been added into the models without really knowing if they are necessary, or can be tested observationally. This relates, among other things, to differential rotation vs. solid body models, disk-(or planet)-locking, and magnetic saturation. By measuring stellar rotation very precisely, without aliasing and other non-uniquenesses like, e.g., v sin i that have infected prior data, as a function of stellar mass/color and as a function of stellar age, these observations will simply remove wiggle-room for the models, and specify the rotational evolution of stars empirically. The observations therefore will have a usefulness beyond the testing of any theoretical models. In fact, our survey might lead to a re-evaluation of what is (un-)necessary in the models.We therefore propose to determine, from precise time-series CCD photometry, a large number (≥1,000) of rotation periods for low-mass (mid F, G, K, and early M-type) stars in 12 nearby open clusters with ages between 50 Myr and 1.5 Gyr. At the end of this survey, called the STELLA Open Cluster survey, we will know unambiguously, the main-sequence rotational evolution of FGKM stars as a function of age. The details of the observationally determined dependencies can then be used to understand the global dependencies. The theoretical models would then be stripped down to the bare essentials, and then rebuilt to comply with observations, removing superfluous effects and identifying new dependencies.