Algols中的临界旋转吸积体与非保守演化
Critically-rotating accretors and non-conservative evolution in Algols
摘要：
在大陵五系统的质量转移阶段，大量的质量和角动量被加速到临界开普勒速度的增益星吸积。一旦达到这个临界值，赢家的命运就不清楚了。我们研究了半分离双星系统中的轨道和恒星自旋演化，特别是对于具有快速旋转吸积体的系统。我们的目的是更好地区分不同的自旋下降机制，提出了一致的解释在Algols的最终状态观察到的缓慢旋转，并评估由于热点的形成的非保守性的程度。我们使用我们的国家的最先进的二进制演化代码，Binstar，其中包含了详细的治疗轨道和恒星的自旋，包括所有的扭矩由于质量转移，恒星和它的吸积盘之间的相互作用，潮汐效应和磁制动。我们还提出了一个新的处方的质量损失，由于形成一个热点的基础上的能量守恒。星形和圆盘之间通过边界层的耦合防止增益器超过临界旋转。磁场效应，虽然操作，是不是占主导地位的自旋下降机制，为敏感的磁场强度。由于潮汐引起的自旋下降是2-4个数量级，太弱而不能补偿由于质量吸积引起的自旋上升扭矩。此外，我们发现最终的分离强烈依赖于自旋下降机制。热点的形成导致在质量传递的快速阶段期间质量损失的大事件。保守性的程度很大程度上取决于受冲击材料的不透明度。需要进行统计研究和新的观测约束，以找到最佳参数集（磁场强度，热点几何形状，.）来重现大陵五的演化
英文摘要：
During the mass-transfer phase in Algol systems, a large amount of mass and angular momentum are accreted by the gainer star which can be accelerated up to its critical Keplerian velocity. The fate of the gainer once it reaches this critical value is unclear. We investigate the orbital and stellar spin evolution in semi-detached binary systems, specifically for systems with rapidly rotating accretors. Our aim is to better distinguish between the different spin-down mechanisms proposed which can consistently explain the slow rotation observed in Algols' final states and assess the degree of non-conservatism due to the formation of a hotspot. We use our state-of-the-art binary evolution code, Binstar, which incorporates a detailed treatment of the orbital and stellar spin, including all torques due to mass transfer, the interactions between a star and its accretion disc, tidal effects and magnetic braking. We also present a new prescription for mass loss due to the formation of a hotspot based on energy conservation. The coupling between the star and the disc via the boundary layer prevents the gainer from exceeding the critical rotation. Magnetic-field effects, although operating, are not the dominant spin-down mechanism for sensible field strengths. Spin down owing to tides is 2-4 orders of magnitudes too weak to compensate the spinning-up torque due to mass accretion. Moreover, we find that the final separation strongly depends on the spin-down mechanism. The formation of a hotspot leads to a large event of mass loss during the rapid phase of mass transfer. The degree of conservatism strongly depends on the opacity of the impacted material. A statistical study as well as new observational constraints are needed to find the optimal set of parameters (magnetic-field strength, hotspot geometry,...) to reproduce Algol evolutions.
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