Rotational evolution of slow-rotator sequence stars
Rotational evolution of slow-rotator sequence stars
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慢自转序列恒星的自转演化
DOI：
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发表时间：
2015
期刊：
影响因子：
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通讯作者：
F. Spada
中科院分区：
文献类型：
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作者：
A. Lanzafame;F. Spada
在疏散星系团中观测到的质量-年龄-自转关系显示了慢旋序列的逐步发展。在这个序列上观察到的星团表明，它对应于某种平衡或渐近条件，而这些条件仍然缺乏完整的理论解释，这对我们理解恒星角动量演化至关重要。我们将考虑内部差动旋转的旋转演化模型与风制动定律的经典和新建议相结合，并使用MCMC方法对模型进行拟合。描述慢转星序列的演化需要考虑角动量从辐射核到对流包层的传递，我们发现，在质量为0.85-1.10$M_(-7.28)$的质量范围内，慢转星序列中恒星的核-包耦合时间尺度为$M^-7.28$。准固体自转只有在1-2 Gyr之后才能实现，这取决于恒星的质量，这意味着观测到与Skumanich定律($P\proto\Sqrt{t}$)的小偏差将需要比目前可用的更老的开放星系团的周期数据。假定风的角动量损失与对流翻转时间尺度和恒星转动惯量成正比的经验质量依赖关系，最好地再现了观测到的0.1-2.5Gyr年龄范围和0.85-1.10$M质量范围内的演化。基于我们的MCMC拟合的周期等时线提供了一种从质量和自转周期推断类太阳主序星的恒星年龄的工具，在很大程度上独立于所采用的风制动模型。它们有效地代表了回转年代学关系，其中考虑了恒星角动量演化的两区模型的物理意义。
The observed mass-age-rotation relationship in open clusters shows the progressive development of a slow-rotators sequence. The observed clustering on this sequence suggests that it corresponds to some equilibrium or asymptotic condition that still lacks a complete theoretical interpretation, crucial to our understanding of the stellar angular momentum evolution. We couple a rotational evolution model, which takes into account internal differential rotation, with classical and new proposals for the wind braking law, and fit models to the data using a MCMC method. The description of the evolution of the slow-rotators sequence requires taking into account the transfer of angular momentum from the radiative core to the convective envelope; we find that, in the mass range 0.85-1.10 $M_{\odot}$, the core-envelope coupling time-scale for stars in the slow-rotators sequence scales as $M^{-7.28}$. Quasi-solid body rotation is achieved only after 1-2 Gyr, depending on stellar mass, which implies that observing small deviations from the Skumanich law ($P \propto \sqrt{t}$) would require period data of older open clusters than available to date. The observed evolution in the 0.1-2.5 Gyr age range and in the 0.85-1.10 $M_{\odot}$ mass range is best reproduced by assuming an empirical mass dependence of the wind angular momentum loss proportional to the convective turnover time-scale and to the stellar moment of inertia. Period isochrones based on our MCMC fit provide a tool for inferring stellar ages of solar-like main-sequence stars from their mass and rotation period largely independent from the wind braking model adopted. These effectively represent gyro-chronology relationships that take into account the physics of the two-zone model for the stellar angular momentum evolution.