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arXiv 0709.4186astro-ph
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磁激变变星的吸积流和演化

The Accretion Flows and Evolution of Magnetic Cataclysmic Variables

A. J. Norton, O. W. Butters, T. L. Parker, G. A. Wynn

摘要:

我们利用磁吸积模型研究了激变变星的吸积流。数值模拟表明,四种类型的流动是可能的:盘,流,环和螺旋桨。对于给定的质量比,决定吸积流的基本观测量是系统的自旋-轨道周期比。如果IP以平衡自旋速率吸积,那么对于质量比为0.5,Pspin/Porb < 0.1的IP将是盘状的,0.1 < Pspin/Porb < 0.6的IP将是流状的,而Pspin/Porb ~ 0.6的IP将是环状的。当恒星成分的质量比降低时,系统在这些流类型之间过渡的自旋与轨道周期比增加。我们第一次提出了mCV的演化轨迹,可以调查它们的吸积流如何随时间变化。当系统演化到更短的轨道周期和更小的质量比时,为了维持自旋平衡,它们的自旋与轨道周期比通常会增加。因此,在短轨道周期内,环状流的相对出现将增加,而盘状流的出现将减少。越来越多的系统在高自旋-轨道周期比下观测到轨道周期低于2小时,以及EX Hya中环状吸积的观测证据,与这张照片完全一致。

英文摘要:

We have used a model of magnetic accretion to investigate the accretion flows of magnetic cataclysmic variables. Numerical simulations demonstrate that four types of flow are possible: discs, streams, rings and propellers. The fundamental observable determining the accretion flow, for a given mass ratio, is the spin-to-orbital period ratio of the system. If IPs are accreting at their equilibrium spin rates, then for a mass ratio of 0.5, those with Pspin/Porb < 0.1 will be disc-like, those with 0.1 < Pspin/Porb < 0.6 will be stream-like, and those with Pspin/Porb ~ 0.6 will be ring-like. The spin to orbital period ratio at which the systems transition between these flow types increases as the mass ratio of the stellar components decreases. For the first time we present evolutionary tracks of mCVs which allow investigation of how their accretion flow changes with time. As systems evolve to shorter orbital periods and smaller mass ratios, in order to maintain spin equilibrium, their spin-to-orbital period ratio will generally increase. As a result, the relative occurrence of ring-like flows will increase, and the occurrence of disc-like flows will decrease, at short orbital periods. The growing number of systems observed at high spin-to-orbital period ratios with orbital periods below 2h, and the observational evidence for ring-like accretion in EX Hya, are fully consistent with this picture.

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