The Angular Momentum Evolution of 0.1-10 M☉ Stars from the Birth Line to the Main Sequence
The Angular Momentum Evolution of 0.1-10 M☉ Stars from the Birth Line to the Main Sequence
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DOI：
10.1086/380503
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发表时间：
2003-10
期刊：
影响因子：
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通讯作者：
S. Wolff;S. Strom;L. Hillenbrand
中科院分区：
文献类型：
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作者：
S. Wolff;S. Strom;L. Hillenbrand
已测量了位于猎户座恒星形成复合体中质量在 0.4 至大于 10 M☉（中位质量 2.1 M☉）的 145 颗恒星样本的预计旋转速度 (v sin i)。这些测量结果还补充了质量低至 0.1 M☉ 的猎户座恒星文献数据。对这些数据分析的主要发现是，对于质量在 ~0.1 至 ~3 M☉ 范围内的对流轨道上的恒星，每单位质量 (J/M) 角动量观测值的上包络变化为 M0.25。这个幂律平稳地延伸到更大质量恒星（3-10 M☉）的领域，这些恒星在猎户座中已经处于零年龄主序带上。这一结果与主序星的特性形成鲜明对比，主序星显示出幂律的破坏，并且对于 M < 2 M☉ 的恒星，随着质量的减小，J/M 急剧下降。我们研究的第二个结果是，这种断裂已经在猎户座样本中位于辐射轨道上的前主序恒星中出现，尽管这些恒星的年龄只有几百万年。对对流-辐射边界两侧恒星旋转速率的比较表明，在从对流轨道过渡到辐射轨道期间，恒星不会像固体一样旋转。作为如何利用观测结果来约束控制早期恒星角动量的过程的初步论证，我们表明，数据的总体趋势可以通过简单的模型来解释，该模型假设恒星（1）在沉积在诞生线上之前就失去了角动量，这似乎是通过星盘相互作用而发生的； (2) 当它们沿着对流轨迹发展时经历额外的制动； (3) 在对流-辐射转变过程中会发生核心-包络线解耦。
Projected rotational velocities (v sin i) have been measured for a sample of 145 stars with masses between 0.4 and greater than 10 M☉ (median mass 2.1 M☉) located in the Orion star-forming complex. These measurements have been supplemented with data from the literature for Orion stars with masses as low as 0.1 M☉. The primary finding from analysis of these data is that the upper envelope of the observed values of angular momentum per unit mass (J/M) varies as M0.25 for stars on convective tracks having masses in the range ~0.1 to ~3 M☉. This power law extends smoothly into the domain of more massive stars (3-10 M☉), which in Orion are already on the zero-age main sequence. This result stands in sharp contrast to the properties of main-sequence stars, which show a break in the power law and a sharp decline in J/M with decreasing mass for stars with M < 2 M☉. A second result of our study is that this break is seen already among the pre-main-sequence stars in our Orion sample that are on radiative tracks, even though these stars are only a few million years old. A comparison of rotation rates seen for stars on either side of the convective-radiative boundary shows that stars do not rotate as solid bodies during the transition from convective to radiative tracks. As a preliminary demonstration of how observations can be used to constrain the processes that control early stellar angular momentum, we show that the broad trends in the data can be accounted for by simple models that posit that stars (1) lose angular momentum before they are deposited on the birth line, plausibly through star-disk interactions; (2) undergo additional braking as they evolve down their convective tracks; and (3) are subject to core-envelope decoupling during the convective-radiative transition.