地表古磁场对大质量恒星演化的影响：I.磁场演化、质量损失淬火和磁制动
The effects of surface fossil magnetic fields on massive star evolution: I. Magnetic field evolution, mass-loss quenching and magnetic braking
摘要：
表面磁场对恒星的质量损失和旋转有很大的影响，因此，对大质量恒星的演化有很大的影响。在这项工作中，我们研究了一个不断发展的偶极表面化石磁场与初始场强为4 kG的15 M的$_{\odot}$太阳金属丰度模型使用日内瓦恒星演化代码的特性的影响。考虑两种不同的情况下的内部角动量输运的非旋转和旋转模型进行了计算，包括磁场演变，质量损失淬火，和磁制动。磁场演化导致最初强的磁场减弱，然而，在我们的模型中，当恒星向红超巨星阶段演化时，仍然保持着可观察到的磁场。在给定的初始质量的模型，质量损失淬火是适度的。磁制动大大提高了化学元素的混合，如果径向差分旋转是允许的，另一方面，列入表面磁场产生一个较低的表面富集的情况下，近固体旋转。包括表面磁场的模型在亨特图（绘制氮丰度与$v \sin i$）上显示出与不包括表面磁场的模型明显不同的趋势。磁模型同意定性与异常的“第2组恒星”，显示缓慢的表面旋转和高表面氮增强的主要序列。
英文摘要：
Surface magnetic fields have a strong impact on stellar mass loss and rotation and, as a consequence, on the evolution of massive stars. In this work we study the influence of an evolving dipolar surface fossil magnetic field with an initial field strength of 4 kG on the characteristics of 15 M$_{\odot}$ solar metallicity models using the Geneva stellar evolution code. Non-rotating and rotating models considering two different scenarios for internal angular momentum transport are computed, including magnetic field evolution, mass-loss quenching, and magnetic braking. Magnetic field evolution results in weakening the initially strong magnetic field, however, in our models an observable magnetic field is still maintained as the star evolves towards the red supergiant phase. At the given initial mass of the models, mass-loss quenching is modest. Magnetic braking greatly enhances chemical element mixing if radial differential rotation is allowed for, on the other hand, the inclusion of surface magnetic fields yields a lower surface enrichment in the case of near solid-body rotation. Models including surface magnetic fields show notably different trends on the Hunter diagram (plotting nitrogen abundance vs $v \sin i$) compared to those that do not. The magnetic models agree qualitatively with the anomalous `Group 2 stars', showing slow surface rotation and high surface nitrogen enhancement on the main sequence.
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